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  • 1.
    Andersson, L.
    et al.
    Univ Colorado, LASP, Boulder, CO 80309 USA..
    Ergun, R. E.
    Univ Colorado, LASP, Boulder, CO 80309 USA.;Univ Colorado, APS, Boulder, CO 80309 USA..
    Delory, G. T.
    Univ Calif Berkeley, SSL, Berkeley, CA 94720 USA..
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Westfall, J.
    Univ Colorado, LASP, Boulder, CO 80309 USA..
    Reed, H.
    Univ Colorado, LASP, Boulder, CO 80309 USA..
    McCauly, J.
    Univ Calif Berkeley, SSL, Berkeley, CA 94720 USA..
    Summers, D.
    Univ Colorado, LASP, Boulder, CO 80309 USA..
    Meyers, D.
    Univ Colorado, LASP, Boulder, CO 80309 USA..
    The Langmuir Probe and Waves (LPW) Instrument for MAVEN2015In: Space Science Reviews, ISSN 0038-6308, E-ISSN 1572-9672, Vol. 195, no 1-4, p. 173-198Article, review/survey (Refereed)
    Abstract [en]

    We describe the sensors, the sensor biasing and control, the signal-processing unit, and the operation of the Langmuir Probe and Waves (LPW) instrument on the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. The LPW instrument is designed to measure the electron density and temperature in the ionosphere of Mars and to measure spectral power density of waves (DC-2 MHz) in Mars' ionosphere, including one component of the electric field. Low-frequency plasma waves can heat ions resulting in atmospheric loss. Higher-frequency waves are used to calibrate the density measurement and to study strong plasma processes. The LPW is part of the Particle and Fields (PF) suite on the MAVEN spacecraft. The LPW instrument utilizes two, 40 cm long by 0.635 cm diameter cylindrical sensors with preamplifiers, which can be configured to measure either plasma currents or plasma waves. The sensors are mounted on a pair of meter long stacer booms. The sensors and nearby surfaces are controlled by a Boom Electronics Board (BEB). The Digital Fields Board (DFB) conditions the analog signals, converts the analog signals to digital, processes the digital signals including spectral analysis, and packetizes the data for transmission. The BEB and DFB are located inside of the Particle and Fields Digital Processing Unit (PFDPU).

  • 2.
    Andersson, L.
    et al.
    Univ Colorado, Atmospher & Space Phys Lab, Boulder, CO 80303 USA..
    Weber, T. D.
    Univ Colorado, Atmospher & Space Phys Lab, Boulder, CO 80303 USA..
    Malaspina, D.
    Univ Colorado, Atmospher & Space Phys Lab, Boulder, CO 80303 USA..
    Crary, F.
    Univ Colorado, Atmospher & Space Phys Lab, Boulder, CO 80303 USA..
    Ergun, R. E.
    Univ Colorado, Atmospher & Space Phys Lab, Boulder, CO 80303 USA..
    Delory, G. T.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Fowler, C. M.
    Univ Colorado, Atmospher & Space Phys Lab, Boulder, CO 80303 USA..
    Morooka, M. W.
    Univ Colorado, Atmospher & Space Phys Lab, Boulder, CO 80303 USA..
    McEnulty, T.
    Univ Colorado, Atmospher & Space Phys Lab, Boulder, CO 80303 USA..
    Eriksson, Anders. I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Andrews, David. J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Horanyi, M.
    Univ Colorado, Atmospher & Space Phys Lab, Boulder, CO 80303 USA..
    Collette, A.
    Univ Colorado, Atmospher & Space Phys Lab, Boulder, CO 80303 USA..
    Yelle, R.
    Univ Arizona, Lunar & Planetary Lab, Tucson, AZ 85721 USA..
    Jakosky, B. M.
    Univ Colorado, Atmospher & Space Phys Lab, Boulder, CO 80303 USA..
    Dust observations at orbital altitudes surrounding Mars2015In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 350, no 6261, article id aad0398Article in journal (Refereed)
    Abstract [en]

    Dust is common close to the martian surface, but no known process can lift appreciable concentrations of particles to altitudes above similar to 150 kilometers. We present observations of dust at altitudes ranging from 150 to above 1000 kilometers by the Langmuir Probe and Wave instrument on the Mars Atmosphere and Volatile Evolution spacecraft. Based on its distribution, we interpret this dust to be interplanetary in origin. A comparison with laboratory measurements indicates that the dust grain size ranges from 1 to 12 micrometers, assuming a typical grain velocity of similar to 18 kilometers per second. These direct observations of dust entering the martian atmosphere improve our understanding of the sources, sinks, and transport of interplanetary dust throughout the inner solar system and the associated impacts on Mars's atmosphere.

  • 3.
    Andrews, David
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Edberg, Niklas J. T.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Gurnett, D. A.
    Morgan, D.
    Nemec, F.
    Opgenoorth, Hermann J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Control of the topside Martian ionosphere by crustal magnetic fields2015In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 4, p. 3042-3058Article in journal (Refereed)
    Abstract [en]

    We present observations from the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) instrument onboard Mars Express of the thermal electron plasma density of the Martian ionosphere and investigate the extent to which it is influenced by the presence of Mars's remnant crustal magnetic fields. We use locally measured electron densities, derived when MARSIS is operating in active ionospheric sounding (AIS) mode, covering an altitude range from approximate to 300km to approximate to 1200km. We compare these measured densities to an empirical model of the dayside ionospheric plasma density in this diffusive transport-dominated regime. We show that small spatial-scale departures from the averaged values are strongly correlated with the pattern of the crustal fields. Persistently elevated densities are seen in regions of relatively stronger crustal fields across the whole altitude range. Comparing these results with measurements of the (scalar) magnetic field also obtained by MARSIS/AIS, we characterize the dayside strength of the draped magnetic fields in the same regions. Finally, we provide a revised empirical model of the plasma density in the Martian ionosphere, including parameterizations for both the crustal field-dominated and draping-dominated regimes.

  • 4.
    Andrews, David J.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Andersson, L.
    Lab Atmospher & Space Phys, Boulder, CO USA..
    Delory, G. T.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Ergun, R. E.
    Lab Atmospher & Space Phys, Boulder, CO USA..
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Fowler, C. M.
    Lab Atmospher & Space Phys, Boulder, CO USA..
    McEnulty, T.
    Lab Atmospher & Space Phys, Boulder, CO USA..
    Morooka, M. W.
    Lab Atmospher & Space Phys, Boulder, CO USA..
    Weber, T.
    Lab Atmospher & Space Phys, Boulder, CO USA..
    Jakosky, B. M.
    Lab Atmospher & Space Phys, Boulder, CO USA..
    Ionospheric plasma density variations observed at Mars by MAVEN/LPW2015In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 21, p. 8862-8869Article in journal (Refereed)
    Abstract [en]

    We report on initial observations made by the Langmuir Probe and Waves relaxation sounding experiment on board the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. These measurements yield the ionospheric thermal plasma density, and we use these data here for an initial survey of its variability. Studying orbit-to-orbit variations, we show that the relative variability of the ionospheric plasma density is lowest at low altitudes near the photochemical peak, steadily increases toward higher altitudes and sharply increases as the spacecraft crosses the terminator and moves into the nightside. Finally, despite the small volume of data currently available, we show that a clear signature of the influence of crustal magnetic fields on the thermal plasma density fluctuations is visible. Such results are consistent with previously reported remote measurements made at higher altitudes, but crucially, here we sample a new span of altitudes between similar to 130 and similar to 300 km using in situ techniques.

  • 5.
    Andrews, David J.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Stergiopoulou, Katerina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Univ Leicester, Sch Phys & Astron, Leicester, England..
    Andersson, Laila
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Ergun, Robert
    Pilinski, Marcin
    Electron densities and temperatures in the Martian ionosphere: MAVEN LPW observations of control by crustal fields2023In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 128, no 3, article id e2022JA031027Article in journal (Refereed)
    Abstract [en]

    Mars Express and Mars Atmosphere and Volatile Evolution (MAVEN) observations have demonstrated the influence of Mars's spatially variable crustal magnetic fields upon the configuration of the plasma in the ionosphere. This influence furthermore leads to variations in ionospheric escape, conceivably in part through the modification of the plasma density and electron temperature in the upper ionosphere. In this study, we examine MAVEN Langmuir Probe and Waves data, finding a clear correspondence between the structure of the crustal fields and both the measured electron temperatures and densities, by first constructing an "average " profile from which departures can be quantified. Electron temperatures are shown to be lower in regions of strong crustal fields over a wide altitude range. We extend previous analyses to cover the nightside ionosphere, finding the same effects present to a lesser degree, in contrast to previous studies where the opposite relationship was found between densities and crustal fields. We further determine the altitude range over which this coupling between both plasma density (and temperature) and crustal fields is effective and use measurements made by MAVEN in the solar wind to explore the dependence of this crustal field control on the coupling to the solar wind and the interplanetary magnetic field (IMF). Based on this, there is some suggestion that variations in the solar wind dynamic pressure are associated with modulation of the effects of the crustal fields on plasma density, whereas the strength of the IMF modulates the crustal fields effects on both electron densities and temperatures.

  • 6.
    André, Mats
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders, I
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Toledo-Redondo, Sergio
    Univ Murcia, Dept Electromagnetism & Elect, Murcia, Spain..
    The Spacecraft Wake: Interference With Electric Field Observations and a Possibility to Detect Cold Ions2021In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 126, no 9, article id e2021JA029493Article in journal (Refereed)
    Abstract [en]

    Wakes behind spacecraft caused by supersonic drifting positive ions are common in plasmas and disturb in situ measurements. We review the impact of wakes on observations by the Electric Field and Wave double-probe instruments on the Cluster satellites. In the solar wind, the equivalent spacecraft charging is small compared to the ion drift energy and the wake effects are caused by the spacecraft body and can be compensated for. We present statistics of the direction, width, and electrostatic potential of wakes, and we compare with an analytical model. In the low-density magnetospheric lobes, the equivalent positive spacecraft charging is large compared to the ion drift energy and an enhanced wake forms. In this case observations of the geophysical electric field with the double-probe technique becomes extremely challenging. Rather, the wake can be used to estimate the flux of cold (eV) positive ions. For an intermediate range of parameters, when the equivalent charging of the spacecraft is similar to the drift energy of the ions, also the charged wire booms of a double-probe instrument must be taken into account. We discuss an example of these effects from the MMS spacecraft near the magnetopause. We find that many observed wake characteristics provide information that can be used for scientific studies. An important example is the enhanced wakes used to estimate the outflow of ionospheric origin in the magnetospheric lobes to about 10 26 cold (eV) ions/s, constituting a large fraction of the mass outflow from planet Earth.

  • 7.
    André, Mats
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Li, K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Outflow of low-energy ions and the solar cycle2015In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 2, p. 1072-1085Article in journal (Refereed)
    Abstract [en]

    Magnetospheric ions with energies less than tens of eV originate from the ionosphere. Positive low-energy ions are complicated to detect onboard sunlit spacecraft at higher altitudes, which often become positively charged to several tens of volts. We use two Cluster spacecraft and study low-energy ions with a technique based on the detection of the wake behind a charged spacecraft in a supersonic ion flow. We find that low-energy ions usually dominate the density and the outward flux in the geomagnetic tail lobes during all parts of the solar cycle. The global outflow is of the order of 10(26) ions/s and often dominates over the outflow at higher energies. The outflow increases by a factor of 2 with increasing solar EUV flux during a solar cycle. This increase is mainly due to the increased density of the outflowing population, while the outflow velocity does not vary much. Thus, the outflow is limited by the available density in the ionospheric source rather than by the energy available in the magnetosphere to increase the velocity.

  • 8.
    André, Mats
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Odelstad, Elias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Graham, Daniel B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Karlsson, T.
    KTH Royal Inst Technol, Sch Elect Engn, Dept Space & Plasma Phys, Stockholm, Sweden.
    Wieser, G. Stenberg
    Swedish Inst Space Phys, Kiruna, Sweden.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Norgren, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Johansson, Fredrik L.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Henri, P.
    Lab Phys & Chim Environm & Espace, Orleans, France.
    Rubin, M.
    Univ Bern, Phys Inst, Bern, Switzerland.
    Richter, I.
    TU Braunschweig, Inst Geophys & Extraterr Phys, Braunschweig, Germany.
    Lower hybrid waves at comet 67P/Churyumov-Gerasimenko2017In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 469, p. S29-S38Article in journal (Refereed)
    Abstract [en]

    We investigate the generation of waves in the lower hybrid frequency range by density gradients in the near plasma environment of comet 67P/Churyumov-Gerasimenko. When the plasma is dominated by water ions from the comet, a situation with magnetized electrons and unmagnetized ions is favourable for the generation of lower hybrid waves. These waves can transfer energy between ions and electrons and reshape the plasma environment of the comet. We consider cometocentric distances out to a few hundred km. We find that when the electron motion is not significantly interrupted by collisions with neutrals, large average gradients within tens of km of the comet, as well as often observed local large density gradients at larger distances, are often likely to be favourable for the generation of lower hybrid waves. Overall, we find that waves in the lower hybrid frequency range are likely to be common in the near plasma environment.

  • 9.
    Bergman, Sofia
    et al.
    Swedish Inst Space Phys, Kiruna, Sweden; Umeå Univ, Dept Phys, Umeå, Sweden.
    Stenberg Wieser, Gabriella
    Swedish Inst Space Phys, Kiruna, Sweden.
    Wieser, Martin
    Swedish Inst Space Phys, Kiruna, Sweden.
    Johansson, Fredrik Leffe
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    The Influence of Varying Spacecraft Potentials and Debye Lengths on In Situ Low-Energy Ion Measurements2020In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 125, no 4, article id e2020JA027870Article in journal (Refereed)
    Abstract [en]

    Low-energy ions are difficult to measure, mainly due to spacecraft charging. The ions are attracted to or repelled from the charged surface prior to detection, which changes both the energy and travel direction of the ions. This results in distortions of the data, and the changed travel directions distort the effective field of view (FOV) of the instrument performing the measurements. The ion composition analyzer (RPC-ICA) was measuring positive ions down to an energy of a few eV around comet 67P/Churyumov-Gerasimenko. Low-energy ions play important parts in processes in the cometary environment, but the FOV of RPC-ICA has been shown to get severely distorted at low ion energies. Several factors are believed to affect the distortion level. In this study we use the Spacecraft Plasma Interaction Software (SPIS) to investigate the influence of varying spacecraft potentials and Debye lengths on the FOV distortion of RPC-ICA. We show that the distortion level is dependent on the Debye length of the surrounding plasma, but the sensitivity varies substantially between different viewing directions of the instrument. We also show that a small nonlinearity exists in the relation between FOV distortion, ion energy, and spacecraft potential, mainly caused by the photoemission and bulk flow of the cometary plasma.

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  • 10.
    Bergman, Sofia
    et al.
    Swedish Inst Space Phys, Kiruna, Sweden.;Umea Univ, Dept Phys, Umea, Sweden..
    Wieser, Gabriella Stenberg
    Swedish Inst Space Phys, Kiruna, Sweden..
    Wieser, Martin
    Swedish Inst Space Phys, Kiruna, Sweden..
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    The Influence of Spacecraft Charging on Low-Energy Ion Measurements Made by RPC-ICA on Rosetta2020In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 125, no 1, article id e2019JA027478Article in journal (Refereed)
    Abstract [en]

    Spacecraft charging is problematic for low-energy plasma measurements. The charged particles are attracted to or repelled from the charged spacecraft, affecting both the energy and direction of travel of the particles. The Ion Composition Analyzer (RPC-ICA) on board the Rosetta spacecraft is suffering from this effect. RPC-ICA was measuring positive ions in the vicinity of comet 67P/Churyumov-Gerasimenko, covering an energy range of a few eV/q to 40 keV/q. The low-energy part of the data is, however, heavily distorted by the negatively charged spacecraft. In this study we use the Spacecraft Plasma Interaction Software to model the influence of the spacecraft potential on the ion trajectories and the corresponding distortion of the field of view (FOV) of the instrument. The results show that the measurements are not significantly distorted when the ion energy corresponds to at least twice the spacecraft potential. Below this energy the FOV is often heavily distorted, but the distortion differs between different viewing directions. Generally, ions entering the instrument close to the aperture plane are less affected than those entering with extreme elevation angles. Plain Language Summary The Rosetta spacecraft followed comet 67P/Churyumov-Gerasimenko for 2 years, providing data giving new insights into the nature of comets. The Ion Composition Analyzer (RPC-ICA) on board the spacecraft measures positive ions in the vicinity of the comet. The instrument can measure low-energy ions, which play an important part in the processes taking place in this environment. To fully understand the environment around the comet, we have to understand these low-energy ions. Unfortunately, this part of the RPC-ICA data is distorted by the spacecraft potential. A spacecraft in space interacts with the surrounding environment, which charges the spacecraft surface to a positive or negative potential. Rosetta was commonly charged to a negative potential throughout the mission, which means that the positive ions measured by RPC-ICA were attracted to the spacecraft. Consequently, both the energy and the travel direction of the ions changed before detection. We investigate how the low-energy ions measured by RPC-ICA have been affected by the spacecraft potential. We use the Spacecraft Plasma Interaction Software to model these effects. The results give us a lower energy limit above which we can trust the measurements and show that some parts of the instrument are more heavily affected than others.

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  • 11.
    Bergman, Sofia
    et al.
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden.;Umeå Univ, Dept Phys, SE-90187 Umeå, Sweden..
    Wieser, Gabriella Stenberg
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden..
    Wieser, Martin
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden..
    Johansson, Fredrik Leffe
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Nilsson, Hans
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden..
    Nemeth, Zoltan
    Wigner Res Ctr Phys, Konkoly Thege M Rd 29-33, H-1121 Budapest, Hungary..
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Williamson, Hayley
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden..
    Ion bulk speeds and temperatures in the diamagnetic cavity of comet 67P from RPC-ICA measurements2021In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 503, no 2, p. 2733-2745Article in journal (Refereed)
    Abstract [en]

    Y Comets are constantly interacting with the solar wind. When the comet activity is high enough, this leads to the creation of a magnetic field free region around the nucleus known as the diamagnetic cavity. It has been suggested that the ion-neutral drag force is balancing the magnetic pressure at the cavity boundary, but after the visit of Rosetta to comet 67P/Churyumov-Gerasimenko the coupling between ions and neutrals inside the cavity has been debated, at least for moderately active comets. In this study, we use data from the ion composition analyser to determine the bulk speeds and temperatures of the low-energy ions in the diamagnetic cavity of comet 67P. The low-energy ions are affected by the negative spacecraft potential, and we use the Spacecraft Plasma Interaction Software to model the resulting influence on the detected energy spectra. We find bulk speeds of 5-10 km s(-1) with a most probable speed of 7 km s(-1), significantly above the velocity of the neutral particles. This indicates that the collisional coupling between ions and neutrals is not strong enough to keep the ions at the same speed as the neutrals inside the cavity. The temperatures are in the range 0.7-1.6 eV, with a peak probability at 1.0 eV. We attribute the major part of the temperature to the fact that ions are born at different locations in the coma, and hence are accelerated over different distances before reaching the spacecraft.

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  • 12.
    Bergman, Sofia
    et al.
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden.;Umeå Univ, Dept Phys, SE-90187 Umeå, Sweden..
    Wieser, Gabriella Stenberg
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden..
    Wieser, Martin
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden..
    Nilsson, Hans
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden..
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Beth, Arnaud
    Umeå Univ, Dept Phys, SE-90187 Umeå, Sweden..
    Masunaga, Kei
    Japan Aerosp Explorat Agcy, Inst Space & Astronaut Sci, Chuo Ku, Yoshinodai 3-1-1, Sagamihara, Kanagawa 2525210, Japan..
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Flow directions of low-energy ions in and around the diamagnetic cavity of comet 67P2021In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 507, no 4, p. 4900-4913Article in journal (Refereed)
    Abstract [en]

    The flow direction of low-energy ions around comet 67P/Churyumov-Gerasimenko has previously been difficult to constrain due to the influence of the spacecraft potential. The Ion Composition Analyzer of the Rosetta Plasma Consortium (RPC-ICA) on Rosetta measured the distribution function of positive ions with energies down to just a few eV/q throughout the escort phase of the mission. Unfortunately, the substantial negative spacecraft potential distorted the directional information of the low-energy data. In this work, we present the flow directions of low-energy ions around comet 67P, corrected for the spacecraft potential using Particle-In-Cell simulation results. We focus on the region in and around the diamagnetic cavity, where low-energy ions are especially important for the dynamics. We separate between slightly accelerated 'burst' features and a more constant 'band' of low-energy ions visible in the data. The 'bursts' are flowing radially outwards from the nucleus with an antisunward component while the 'band' is predominantly streaming back towards the comet. This provides evidence of counter-streaming ions, which has implications for the overall expansion velocity of the ions. The backstreaming ions are present also at times when the diamagnetic cavity was not detected, indicating that the process accelerating the ions back towards the comet is not connected to the cavity boundary.

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  • 13.
    Breuillard, H.
    et al.
    Univ Orleans, CNES, CNRS, UMR7328,LPC2E, Orleans, France;Univ Paris Sud, Sorbonne Univ, Ecole Polytech, UMR7648 CNRS,Lab Phys Plasmas, Paris, France.
    Henri, P.
    Univ Orleans, CNES, CNRS, UMR7328,LPC2E, Orleans, France.
    Bucciantini, L.
    Univ Orleans, CNES, CNRS, UMR7328,LPC2E, Orleans, France.
    Volwerk, M.
    Austrian Acad Sci, Space Res Inst, Graz, Austria.
    Karlsson, T.
    KTH Royal Inst Technol, Stockholm, Sweden.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Odelstad, E.
    Swedish Inst Space Phys, Uppsala, Sweden.
    Richter, I
    Tech Univ Carolo Wilhelmina Braunschweig, Braunschweig, Germany.
    Goetz, C.
    Tech Univ Carolo Wilhelmina Braunschweig, Braunschweig, Germany.
    Vallieres, X.
    Univ Orleans, CNES, CNRS, UMR7328,LPC2E, Orleans, France.
    Hajra, R.
    Univ Orleans, CNES, CNRS, UMR7328,LPC2E, Orleans, France;Natl Atmospher Res Lab, Tirupati, Andhra Pradesh, India.
    Properties of the singing comet waves in the 67P/Churyumov-Gerasimenko plasma environment as observed by the Rosetta mission2019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 630, article id A39Article in journal (Refereed)
    Abstract [en]

    Using in situ measurements from different instruments on board the Rosetta spacecraft, we investigate the properties of the newly discovered low-frequency oscillations, known as singing comet waves, that sometimes dominate the close plasma environment of comet 67P/Churyumov-Gerasimenko. These waves are thought to be generated by a modified ion-Weibel instability that grows due to a beam of water ions created by water molecules that outgass from the comet. We take advantage of a cometary outburst event that occurred on 2016 February 19 to probe this generation mechanism. We analyze the 3D magnetic field waveforms to infer the properties of the magnetic oscillations of the cometary ion waves. They are observed in the typical frequency range (similar to 50 mHz) before the cometary outburst, but at similar to 20 mHz during the outburst. They are also observed to be elliptically right-hand polarized and to propagate rather closely (similar to 0-50 degrees) to the background magnetic field. We also construct a density dataset with a high enough time resolution that allows us to study the plasma contribution to the ion cometary waves. The correlation between plasma and magnetic field variations associated with the waves indicates that they are mostly in phase before and during the outburst, which means that they are compressional waves. We therefore show that the measurements from multiple instruments are consistent with the modified ion-Weibel instability as the source of the singing comet wave activity. We also argue that the observed frequency of the singing comet waves could be a way to indirectly probe the strength of neutral plasma coupling in the 67P environment.

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  • 14.
    Broiles, Thomas W.
    et al.
    Southwest Res Inst, Div Space Sci & Engn, 6220 Culebra Rd, San Antonio, TX 78238 USA..
    Burch, J. L.
    Southwest Res Inst, Div Space Sci & Engn, 6220 Culebra Rd, San Antonio, TX 78238 USA..
    Chae, K.
    Southwest Res Inst, Div Space Sci & Engn, 6220 Culebra Rd, San Antonio, TX 78238 USA..
    Clark, G.
    Johns Hopkins Univ, Appl Phys Lab, 11100 Johns Hopkins Rd, Laurel, MD 20723 USA..
    Cravens, T. E.
    Univ Kansas, Dept Phys & Astron, 1450 Jayhawk Blvd, Lawrence, KS 66045 USA..
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Fuselier, S. A.
    Southwest Res Inst, Div Space Sci & Engn, 6220 Culebra Rd, San Antonio, TX 78238 USA.;Univ Texas San Antonio, Dept Phys & Astron, San Antonio, TX 78249 USA..
    Frahm, R. A.
    Southwest Res Inst, Div Space Sci & Engn, 6220 Culebra Rd, San Antonio, TX 78238 USA..
    Gasc, S.
    Univ Bern, Phys Inst, Sidlerstr 5, CH-3012 Bern, Switzerland..
    Goldstein, R.
    Southwest Res Inst, Div Space Sci & Engn, 6220 Culebra Rd, San Antonio, TX 78238 USA..
    Henri, P.
    CNRS, LPC2E, F-45071 Orleans, France..
    Koenders, C.
    Tech Univ Carolo Wilhelmina Braunschweig, Inst Geophys & Extraterr Phys, Mendelssohnstr 3, D-38106 Braunschweig, Germany..
    Livadiotis, G.
    Southwest Res Inst, Div Space Sci & Engn, 6220 Culebra Rd, San Antonio, TX 78238 USA..
    Mandt, K. E.
    Southwest Res Inst, Div Space Sci & Engn, 6220 Culebra Rd, San Antonio, TX 78238 USA.;Univ Texas San Antonio, Dept Phys & Astron, San Antonio, TX 78249 USA..
    Mokashi, P.
    Southwest Res Inst, Div Space Sci & Engn, 6220 Culebra Rd, San Antonio, TX 78238 USA..
    Nemeth, Z.
    Wigner Res Ctr Phys, H-1121 Budapest, Hungary..
    Odelstad, Elias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics. Univ Kansas, Dept Phys & Astron, 1450 Jayhawk Blvd, Lawrence, KS 66045 USA..
    Rubin, M.
    Univ Bern, Phys Inst, Sidlerstr 5, CH-3012 Bern, Switzerland..
    Samara, M.
    Goddard Space Flight Ctr, Heliophys Div, 8800 Greenbelt Rd, Greenbelt, MD 20771 USA..
    Statistical analysis of suprathermal electron drivers at 67P/Churyumov-Gerasimenko2016In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 462, p. S312-S322Article in journal (Refereed)
    Abstract [en]

    We use observations from the Ion and Electron Sensor (IES) on board the Rosetta spacecraft to study the relationship between the cometary suprathermal electrons and the drivers that affect their density and temperature. We fit the IES electron observations with the summation of two kappa distributions, which we characterize as a dense and warm population (similar to 10 cm(-3) and similar to 16 eV) and a rarefied and hot population (similar to 0.01 cm(-3) and similar to 43 eV). The parameters of our fitting technique determine the populations' density, temperature, and invariant kappa index. We focus our analysis on the warm population to determine its origin by comparing the density and temperature with the neutral density and magnetic field strength. We find that the warm electron population is actually two separate sub-populations: electron distributions with temperatures above 8.6 eV and electron distributions with temperatures below 8.6 eV. The two sub-populations have different relationships between their density and temperature. Moreover, the two sub-populations are affected by different drivers. The hotter sub-population temperature is strongly correlated with neutral density, while the cooler sub-population is unaffected by neutral density and is only weakly correlated with magnetic field strength. We suggest that the population with temperatures above 8.6 eV is being heated by lower hybrid waves driven by counterstreaming solar wind protons and newly formed, cometary ions created in localized, dense neutral streams. To the best of our knowledge, this represents the first observations of cometary electrons heated through wave-particle interactions.

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  • 15.
    Buchert, Stephan C.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Gill, Reine
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Nilsson, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Åhlén, Lennart
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Knudsen, David
    Univ Calgary, Calgary, AB, Canada..
    Burchill, Johnathan
    Univ Calgary, Calgary, AB, Canada..
    Archer, William
    Univ Calgary, Calgary, AB, Canada..
    Kouznetsov, Alexei
    Univ Calgary, Calgary, AB, Canada..
    Stricker, Nico
    ESA ESTEC, Noordwijk, Netherlands..
    Bouridah, Abderrazak
    ESA ESTEC, Noordwijk, Netherlands..
    Bock, Ralph
    ESA ESTEC, Noordwijk, Netherlands..
    Haggstrom, Ingemar
    EISCAT Sci Assoc, Headquarters, Kiruna, Sweden..
    Rietveld, Michael
    EISCAT Sci Assoc, Tromso, Norway..
    Gonzalez, Sixto
    Natl Astron & Ionosphere Ctr, Arecibo, PR USA..
    Aponte, Nestor
    Natl Astron & Ionosphere Ctr, Arecibo, PR USA..
    First results from the Langmuir probes on the Swarm satellites2014In: 2014 XXXITH URSI General Assembly And Scientific Symposium (URSI GASS), 2014Conference paper (Refereed)
  • 16.
    Buchert, Stephan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Zangerl, Franz
    Sust, Manfred
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Opgenoorth, Hermann
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    SWARM observations of equatorial electron densities and topside GPS track losses2015In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 7, p. 2088-2092Article in journal (Refereed)
    Abstract [en]

    The SWARM satellites have both upward looking GPS receivers and Langmuir probes. The receivers repeatedly lost track of the L1 band signal in January-February 2014 at postsunset hours, when SWARM was at nearly 500km altitude. This indicates that the signal was disturbed by ionospheric irregularities at this height and above. The track losses occurred right at density gradients associated with equatorial plasma bubbles and predominantly where the measured background density was highest. The signal showed strong phase scintillations rather than in amplitude, indicating that SWARM might be in the near field of an ionospheric phase screen. Density biteouts, depletions between steep gradients, were up to almost 3 orders of magnitude deep in the background of a more shallow trough centered at the magnetic equator. Comparison between satellites shows that the biteout structure strongly varied in longitude over approximate to 100km and has in north-south steep walls.

  • 17.
    Carbone, F.
    et al.
    Univ Calabria, Natl Res Council, Inst Atmospher Pollut Res, I-87036 Arcavacata Di Rende, Italy..
    Sorriso-Valvo, Luca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Ist Sci & Tecnol Plasmi, CNR, Via Amendola 122-D, I-70126 Bari, Italy.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Steinvall, Konrad
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vecchio, A.
    Univ Paris Diderot, Sorbonne Univ, Univ PSL, Observ Paris, Sorbonne Paris Cite,5 Pl Jules Janssen, F-92195 Meudon, France.;Radboud Univ Nijmegen, Res Inst Math Astrophys & Particle Phys, Nijmegen, Netherlands..
    Telloni, D.
    Natl Inst Astrophys, Astrophys Observ Torino, Turin, Italy..
    Yordanova, Emiliya
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Graham, Daniel B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Edberg, Niklas J. T.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Erik P. G.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vásconez, C. L.
    Escuela Politec Nacl, Dept Fis, Ladron de Guevara E11-253, Quito 170525, Ecuador..
    Maksimovic, M.
    Radboud Univ Nijmegen, Res Inst Math Astrophys & Particle Phys, Nijmegen, Netherlands..
    Bruno, R.
    Natl Inst Astrophys INAF, Inst Space Astrophys & Planetol IAPS, Via Fosso del Cavaliere 100, I-00133 Rome, Italy..
    D'Amicis, R.
    Natl Inst Astrophys INAF, Inst Space Astrophys & Planetol IAPS, Via Fosso del Cavaliere 100, I-00133 Rome, Italy..
    Bale, S. D.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA.;Univ Calif Berkeley, Phys Dept, Berkeley, CA 94720 USA..
    Chust, T.
    Univ Paris Saclay, Observ Paris, Sorbonne Univ, Ecole Polytech,LPP,CNRS, Paris, France..
    Krasnoselskikh, V.
    CNRS, LPC2E, 3A Ave Rech Sci, Orleans, France..
    Kretzschmar, M.
    CNRS, LPC2E, 3A Ave Rech Sci, Orleans, France.;Univ Orleans, Orleans, France..
    Lorfèvre, E.
    CNES, 18 Ave Edouard Belin, F-31400 Toulouse, France..
    Plettemeier, D.
    Tech Univ Dresden, Wurzburger Str 35, D-01187 Dresden, Germany..
    Soucek, J.
    Czech Acad Sci, Inst Atmospher Phys, Prague, Czech Republic..
    Steller, M.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Stverák, S.
    Czech Acad Sci, Inst Atmospher Phys, Prague, Czech Republic.;Czech Acad Sci, Astron Inst, Prague, Czech Republic..
    Trávnicek, P.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA.;Czech Acad Sci, Inst Atmospher Phys, Prague, Czech Republic..
    Vaivads, A.
    CNRS, LPC2E, 3A Ave Rech Sci, Orleans, France.;Royal Inst Technol, Sch Elect Engn & Comp Sci, Dept Space & Plasma Phys, Stockholm, Sweden..
    Horbury, T. S.
    Imperial Coll London, Blackett Lab, Space & Atmospher Phys, London SW7 2AZ, England..
    O'Brien, H.
    Imperial Coll London, Blackett Lab, Space & Atmospher Phys, London SW7 2AZ, England..
    Angelini, V.
    Imperial Coll London, Blackett Lab, Space & Atmospher Phys, London SW7 2AZ, England..
    Evans, V.
    Imperial Coll London, Blackett Lab, Space & Atmospher Phys, London SW7 2AZ, England..
    Statistical study of electron density turbulence and ion-cyclotron waves in the inner heliosphere: Solar Orbiter observations2021In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 656, article id A16Article in journal (Refereed)
    Abstract [en]

    Context. The recently released spacecraft potential measured by the RPW instrument on board Solar Orbiter has been used to estimate the solar wind electron density in the inner heliosphere.

    Aims. The measurement of the solar wind’s electron density, taken in June 2020, has been analysed to obtain a thorough characterization of the turbulence and intermittency properties of the fluctuations. Magnetic field data have been used to describe the presence of ion-scale waves.

    Methods. To study and quantify the properties of turbulence, we extracted selected intervals. We used empirical mode decomposition to obtain the generalized marginal Hilbert spectrum, equivalent to the structure functions analysis, which additionally reduced issues typical of non-stationary, short time series. The presence of waves was quantitatively determined by introducing a parameter describing the time-dependent, frequency-filtered wave power.

    Results. A well-defined inertial range with power-law scalng was found almost everywhere in the sample studied. However, the Kolmogorov scaling and the typical intermittency effects are only present in fraction of the samples. Other intervals have shallower spectra and more irregular intermittency, which are not described by models of turbulence. These are observed predominantly during intervals of enhanced ion frequency wave activity. Comparisons with compressible magnetic field intermittency (from the MAG instrument) and with an estimate of the solar wind velocity (using electric and magnetic field) are also provided to give general context and help determine the cause of these anomalous fluctuations.

  • 18.
    Deca, Jan
    et al.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80303 USA.;NASA, SSERVI, Inst Modeling Plasma Atmospheres & Cosm Dus, Moffett Field, CA 94035 USA..
    Divin, Andrey
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. St Petersburg State Univ, Phys Dept, St Petersburg 198504, Russia.
    Henri, Pierre
    CNRS, LPC2E, F-45071 Orleans, France..
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Markidis, Stefano
    KTH Royal Inst Technol, S-10044 Stockholm, Sweden..
    Olshevsky, Vyacheslav
    Katholieke Univ Leuven, Ctr Math Plasma Astrophys CmPA, B-3001 Leuven, Belgium..
    Horányi, Mihály
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80303 USA.;NASA, SSERVI, Inst Modeling Plasma Atmospheres & Cosm Dus, Moffett Field, CA 94035 USA..
    Electron and Ion Dynamics of the Solar Wind Interaction with a Weakly Outgassing Comet2017In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 118, no 20, article id 205101Article in journal (Refereed)
    Abstract [en]

    Using a 3D fully kinetic approach, we disentangle and explain the ion and electron dynamics of the solar wind interaction with a weakly outgassing comet. We show that, to first order, the dynamical interaction is representative of a four-fluid coupled system. We self-consistently simulate and identify the origin of the warm and suprathermal electron distributions observed by ESA's Rosetta mission to comet 67P/Churyumov-Gerasimenko and conclude that a detailed kinetic treatment of the electron dynamics is critical to fully capture the complex physics of mass-loading plasmas.

  • 19.
    Deca, Jan
    et al.
    Univ Colorado, LASP, Boulder, CO 80303 USA;NASA, Inst Modeling Plasma Atmospheres & Cosm Dust, SSERVI, Moffett Field, CA 94035 USA.
    Henri, Pierre
    CNRS, LPC2E, F-45071 Orleans, France;Univ Cote dAzur, Observ Cote dAzur, CNRS, Lab Lagrange, Nice, France.
    Divin, Andrey
    St Petersburg State Univ, Phys Dept, St Petersburg 198504, Russia.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Galand, Marina
    Imperial Coll London, Dept Phys, London SW7 2AZ, England.
    Beth, Arnaud
    Imperial Coll London, Dept Phys, London SW7 2AZ, England.
    Ostaszewski, Katharina
    Tech Univ Carolo Wilhelmina Braunschweig, Inst Geophys & Extraterr Phys IGeP, D-38106 Braunschweig, Germany.
    Horanyi, Mihaly
    Univ Colorado, LASP, Boulder, CO 80303 USA;NASA, Inst Modeling Plasma Atmospheres & Cosm Dust, SSERVI, Moffett Field, CA 94035 USA;Univ Colorado, Dept Phys, Boulder, CO 80309 USA.
    Building a Weakly Outgassing Comet from a Generalized Ohm's Law2019In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 123, no 5, article id 055101Article in journal (Refereed)
    Abstract [en]

    When a weakly outgassing comet is sufficiently close to the Sun, the formation of an ionized coma results in solar wind mass loading and magnetic field draping around its nucleus. Using a 3D fully kinetic approach, we distill the components of a generalized Ohm's law and the effective electron equation of state directly from the self-consistently simulated electron dynamics and identify the driving physics in the various regions of the cometary plasma environment. Using the example of space plasmas, in particular multispecies cometary plasmas, we show how the description for the complex kinetic electron dynamics can be simplified through a simple effective closure, and identify where an isotropic single-electron fluid Ohm's law approximation can be used, and where it fails.

  • 20.
    Divin, Andrey
    et al.
    St Petersburg State Univ, Ulianovskaya 1, St Petersburg 198504, Russia.
    Deca, Jan
    Univ Colorado, LASP, Boulder, CO 80303 USA;NASA, Inst Modeling Plasma Atmospheres & Cosm Dust, SSERVI, Moffett Field, CA 94035 USA.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Henri, Pierre
    CNRS, LPC2E, 3 Ave Rech Sci, F-45071 Orleans, France;UCA, CNRS, OCA, Lab Lagrange, Nice, France.
    Lapenta, Giovanni
    Katholieke Univ Leuven, CmPA, Dept Math, Celestijnenlaan 200B,Bus 2400, B-3001 Leuven, Belgium.
    Olshevsky, Vyacheslav
    KTH Royal Inst Technol, SE-10044 Stockholm, Sweden.
    Markidis, Stefano
    KTH Royal Inst Technol, SE-10044 Stockholm, Sweden.
    A Fully Kinetic Perspective of Electron Acceleration around a Weakly Outgassing Comet2020In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 889, no 2, article id L33Article in journal (Refereed)
    Abstract [en]

    The cometary mission Rosetta has shown the presence of higher-than-expected suprathermal electron fluxes. In this study, using 3D fully kinetic electromagnetic simulations of the interaction of the solar wind with a comet, we constrain the kinetic mechanism that is responsible for the bulk electron energization that creates the suprathermal distribution from the warm background of solar wind electrons. We identify and characterize the magnetic field-aligned ambipolar electric field that ensures quasi-neutrality and traps warm electrons. Solar wind electrons are accelerated to energies as high as 50-70 eV close to the comet nucleus without the need for wave-particle or turbulent heating mechanisms. We find that the accelerating potential controls the parallel electron temperature, total density, and (to a lesser degree) the perpendicular electron temperature and the magnetic field magnitude. Our self-consistent approach enables us to better understand the underlying plasma processes that govern the near-comet plasma environment.

  • 21.
    Edberg, Niklas J. T.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Alho, M.
    Aalto Univ, Sch Elect Engn, Dept Radio Sci & Engn, POB 13000, FI-00076 Aalto, Finland..
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Andrews, David J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Behar, E.
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden..
    Burch, J. L.
    Southwest Res Inst, 6220 Culebra Rd, San Antonio, TX 78238 USA..
    Carr, C. M.
    Imperial Coll London, Exhibit Rd, London SW7 2AZ, England..
    Cupido, E.
    Imperial Coll London, Exhibit Rd, London SW7 2AZ, England..
    Engelhardt, Ilka. A. D.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Glassmeier, K. -H
    Goetz, C.
    TU Braunschweig, Inst Geophys & Extraterr Phys, Mendelssohnstr 3, D-38106 Braunschweig, Germany..
    Goldstein, R.
    Southwest Res Inst, 6220 Culebra Rd, San Antonio, TX 78238 USA..
    Henri, P.
    Lab Phys & Chim Environm & Espace, F-45071 Orleans 2, France..
    Johansson, Fredrik L.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Koenders, C.
    TU Braunschweig, Inst Geophys & Extraterr Phys, Mendelssohnstr 3, D-38106 Braunschweig, Germany..
    Mandt, K.
    Southwest Res Inst, 6220 Culebra Rd, San Antonio, TX 78238 USA.;Univ Texas San Antonio, Dept Phys & Astron, San Antonio, TX 78249 USA..
    Moestl, C.
    Austrian Acad Sci, Space Res Inst, Schmiedlstr 6, A-8042 Graz, Austria..
    Nilsson, H.
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden..
    Odelstad, Elias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Richter, I.
    TU Braunschweig, Inst Geophys & Extraterr Phys, Mendelssohnstr 3, D-38106 Braunschweig, Germany..
    Wedlund, C. Simon
    Univ Oslo, Dept Phys, Box 1048 Blindern, N-0316 Oslo, Norway..
    Wieser, G. Stenberg
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden..
    Szego, K.
    Wigner Res Ctr Phys, Konkoly Thege Miklos Ut 29-33, H-1121 Budapest, Hungary..
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Volwerk, M.
    Austrian Acad Sci, Space Res Inst, Schmiedlstr 6, A-8042 Graz, Austria..
    CME impact on comet 67P/Churyumov-Gerasimenko2016In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 462, p. S45-S56Article in journal (Refereed)
    Abstract [en]

    We present Rosetta observations from comet 67P/Churyumov-Gerasimenko during the impact of a coronal mass ejection (CME). The CME impacted on 2015 Oct 5-6, when Rosetta was about 800 km from the comet nucleus, and 1.4 au from the Sun. Upon impact, the plasma environment is compressed to the level that solar wind ions, not seen a few days earlier when at 1500 km, now reach Rosetta. In response to the compression, the flux of suprathermal electrons increases by a factor of 5-10 and the background magnetic field strength increases by a factor of similar to 2.5. The plasma density increases by a factor of 10 and reaches 600 cm(-3), due to increased particle impact ionization, charge exchange and the adiabatic compression of the plasma environment. We also observe unprecedentedly large magnetic field spikes at 800 km, reaching above 200 nT, which are interpreted as magnetic flux ropes. We suggest that these could possibly be formed by magnetic reconnection processes in the coma as the magnetic field across the CME changes polarity, or as a consequence of strong shears causing Kelvin-Helmholtz instabilities in the plasma flow. Due to the limited orbit of Rosetta, we are not able to observe if a tail disconnection occurs during the CME impact, which could be expected based on previous remote observations of other CME-comet interactions.

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  • 22.
    Edberg, Niklas J. T.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Odelstad, Elias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Henri, P.
    Lebreton, J. -P
    Gasc, S.
    Rubin, M.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Gill, Reine
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Erik P. G.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Carr, C. M.
    Cupido, E.
    Glassmeier, K. -H
    Goldstein, R.
    Koenders, C.
    Mandt, K.
    Nemeth, Z.
    Nilsson, H.
    Richter, I.
    Wieser, G. Stenberg
    Szego, K.
    Volwerk, M.
    Spatial distribution of low-energy plasma around comet 67P/CG from Rosetta measurements2015In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 11, p. 4263-4269Article in journal (Refereed)
    Abstract [en]

    We use measurements from the Rosetta plasma consortium Langmuir probe and mutual impedance probe to study the spatial distribution of low-energy plasma in the near-nucleus coma of comet 67P/Churyumov-Gerasimenko. The spatial distribution is highly structured with the highest density in the summer hemisphere and above the region connecting the two main lobes of the comet, i.e., the neck region. There is a clear correlation with the neutral density and the plasma to neutral density ratio is found to be approximate to 1-210(-6), at a cometocentric distance of 10km and at 3.1AU from the Sun. A clear 6.2h modulation of the plasma is seen as the neck is exposed twice per rotation. The electron density of the collisionless plasma within 260km from the nucleus falls off with radial distance as approximate to 1/r. The spatial structure indicates that local ionization of neutral gas is the dominant source of low-energy plasma around the comet.

  • 23.
    Edberg, Niklas J. T.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Odelstad, Elias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Andrews, D. J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Burch, J. L.
    SW Res Inst, San Antonio, TX USA..
    Carr, C. M.
    Univ London Imperial Coll Sci Technol & Med, Space & Atmospher Phys Grp, London, England..
    Cupido, E.
    Univ London Imperial Coll Sci Technol & Med, Space & Atmospher Phys Grp, London, England..
    Glassmeier, K. -H
    Goldstein, R.
    SW Res Inst, San Antonio, TX USA..
    Halekas, J. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Henri, P.
    Lab Phys & Chim Environm & Espace, Orleans, France..
    Koenders, C.
    TU Braunschweig, Inst Geophys & Extraterr Phys, Braunschweig, Germany..
    Mandt, K.
    SW Res Inst, San Antonio, TX USA..
    Mokashi, P.
    SW Res Inst, San Antonio, TX USA..
    Nemeth, Z.
    Wigner Res Ctr Phys, Budapest, Hungary..
    Nilsson, H.
    Swedish Inst Space Phys, S-98128 Kiruna, Sweden..
    Ramstad, R.
    Swedish Inst Space Phys, S-98128 Kiruna, Sweden..
    Richter, I.
    TU Braunschweig, Inst Geophys & Extraterr Phys, Braunschweig, Germany..
    Wieser, G. Stenberg
    Swedish Inst Space Phys, S-98128 Kiruna, Sweden..
    Solar wind interaction with comet 67P: Impacts of corotating interaction regions2016In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, no 2, p. 949-965Article in journal (Refereed)
    Abstract [en]

    We present observations from the Rosetta Plasma Consortium of the effects of stormy solar wind on comet 67P/Churyumov-Gerasimenko. Four corotating interaction regions (CIRs), where the first event has possibly merged with a coronal mass ejection, are traced from Earth via Mars (using Mars Express and Mars Atmosphere and Volatile EvolutioN mission) to comet 67P from October to December 2014. When the comet is 3.1-2.7AU from the Sun and the neutral outgassing rate approximate to 10(25)-10(26)s(-1), the CIRs significantly influence the cometary plasma environment at altitudes down to 10-30km. The ionospheric low-energy (approximate to 5eV) plasma density increases significantly in all events, by a factor of >2 in events 1 and 2 but less in events 3 and 4. The spacecraft potential drops below -20V upon impact when the flux of electrons increases. The increased density is likely caused by compression of the plasma environment, increased particle impact ionization, and possibly charge exchange processes and acceleration of mass-loaded plasma back to the comet ionosphere. During all events, the fluxes of suprathermal (approximate to 10-100eV) electrons increase significantly, suggesting that the heating mechanism of these electrons is coupled to the solar wind energy input. At impact the magnetic field strength in the coma increases by a factor of 2-5 as more interplanetary magnetic field piles up around the comet. During two CIR impact events, we observe possible plasma boundaries forming, or moving past Rosetta, as the strong solar wind compresses the cometary plasma environment. We also discuss the possibility of seeing some signatures of the ionospheric response to tail disconnection events.

  • 24.
    Edberg, Niklas J. T.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Nilsson, H.
    Swedish Inst Space Phys IRF, Kiruna, Sweden..
    Gunell, H.
    Umeå Univ, Dept Phys, Umeå, Sweden..
    Götz, C.
    Northumbria Univ, Dept Math Phys & Elect Engn, Newcastle Upon Tyne, England..
    Richter, I.
    Tech Univ Carolo Wilhelmina Braunschweig, Inst Geophys & Extraterr Phys, Braunschweig, Germany..
    Henri, P.
    CNRS, Lab Phys & Chim Environm & Espace, F-45071 Orleans, France.;Lab Lagrange, OCA, CNRS, UCA, F-06304 Nice, France..
    De Keyser, J.
    Royal Belgian Inst Space Aeron, BIRA IASB, Brussels, Belgium..
    Scale size of cometary bow shocks2024In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 682, article id A51Article in journal (Refereed)
    Abstract [en]

    Context. In past decades, several spacecraft have visited comets to investigate their plasma environments. In the coming years, Comet Interceptor will make yet another attempt. This time, the target comet and its outgassing activity are unknown and may not be known before the spacecraft has been launched into its parking orbit, where it will await a possible interception. If the approximate outgassing rate can be estimated remotely when a target has been identified, it is desirable to also be able to estimate the scale size of the plasma environment, defined here as the region bound by the bow shock.

    Aims. This study aims to combine previous measurements and simulations of cometary bow shock locations to gain a better understanding of how the scale size of cometary plasma environments varies. We compare these data with models of the bow shock size, and we furthermore provide an outgassing rate-dependent shape model of the bow shock. We then use this to predict a range of times and cometocentric distances for the crossing of the bow shock by Comet Interceptor, together with expected plasma density measurements along the spacecraft track.

    Methods. We used data of the location of cometary bow shocks from previous spacecraft missions, together with simulation results from previously published studies. We compared these results with an existing model of the bow shock stand-off distance and expand on this to provide a shape model of cometary bow shocks. The model in particular includes the cometary outgassing rate, but also upstream solar wind conditions, ionisation rates, and the neutral flow velocity.

    Results. The agreement between the gas-dynamic model and the data and simulation results is good in terms of the stand-off distance of the bow shock as a function of the outgassing rate. For outgassing rates in the range of 1027–1031–s-1, the scale size of cometary bow shocks can vary by four orders of magnitude, from about 102 km to 106 km, for an ionisation rate, flow velocity, and upstream solar wind conditions typical of those at 1 AU. The proposed bow shock shape model shows that a comet plasma environment can range in scale size from the plasma environment of Mars to about half of that of Saturn.

    Conclusions. The model-data agreement allows for the planning of upcoming spacecraft comet encounters, such as that of Comet Interceptor, when a target has been identified and its outgassing rate is determined. We conclude that the time a spacecraft can spend within the plasma environment during a flyby can range from minutes to days, depending on the comet that is visited and on the flyby speed. However, to capture most of the comet plasma environment, including pick-up ions and upstream plasma waves, and to ensure the highest possible scientific return, measurements should still start well upstream of the expected bow shock location. From the plasma perspective, the selected target should preferably be an active comet with the lowest possible flyby velocity.

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  • 25.
    Edberg, Niklas J. T.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Goetz, Charlotte
    Tech Univ Carolo Wilhelmina Braunschweig, Inst Geophys & Extraterr Phys, Braunschweig, Germany.
    Nilsson, Hans
    Swedish Inst Space Phys, POB 812, SE-98128 Kiruna, Sweden;Lulea Univ Technol, Dept Comp Sci Elect & Space Engn, Rymdcampus 1, SE-98128 Kiruna, Sweden.
    Gilet, Nicolas
    CNRS, LPC2E, Orleans, France.
    Henri, Pierre
    CNRS, LPC2E, Orleans, France.
    The Convective Electric Field Influence on the Cold Plasma and Diamagnetic Cavity of Comet 67P2019In: Astronomical Journal, ISSN 0004-6256, E-ISSN 1538-3881, Vol. 158, no 2, article id 71Article in journal (Refereed)
    Abstract [en]

    We studied the distribution of cold electrons (<1 eV) around comet 67P/Churyumov-Gerasimenko with respect to the solar wind convective electric field direction. The cold plasma was measured by the Langmuir Probe instrument and the direction of the convective electric field E-conv = -nu x B was determined from magnetic field (B) measurements inside the coma combined with an assumption of a purely radial solar wind velocity nu. We found that the cold plasma is twice as likely to be observed when the convective electric field at Rosetta's position is directed toward the nucleus (in the -E(conv )hemisphere) compared to when it is away from the nucleus (in the +E-conv hemisphere). Similarly, the diamagnetic cavity, in which previous studies have shown that cold plasma is always present, was also found to be observed twice as often when in the -E-conv hemisphere, linking its existence circumstantially to the presence of cold electrons. The results are consistent with hybrid and Hall magnetohydrodynamic simulations as well as measurements of the ion distribution around the diamagnetic cavity.

  • 26.
    Edberg, Niklas J. T.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Andrews, David J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Hajra, R.
    CNRS, LPC2E, Orleans, France;Natl Atmospher Res Lab, Gadanki 517112, India.
    Henri, P.
    CNRS, LPC2E, Orleans, France.
    Wedlund, C. S.
    Univ Oslo, Dept Phys, Box 1048 Blindern, N-0316 Oslo, Norway.
    Alho, M.
    Aalto Univ, Sch Elect Engn, Dept Radio Sci & Engn, Aalto, Finland.
    Thiemann, E.
    Univ Colorado, Lab Atmospher & Space Phys, 3665 Discovery Dr, Boulder, CO 80303 USA.
    Solar flares observed by Rosetta at comet 67P/Churyumov-Gerasimenko2019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 630, article id A49Article in journal (Refereed)
    Abstract [en]

    Context. The Rosetta spacecraft made continuous measurements of the coma of comet 67P/Churyumov-Gerasimenko (67P) for more than two years. The plasma in the coma appeared very dynamic, and many factors control its variability. Aims. We wish to identify the effects of solar flares on the comet plasma and also their effect on the measurements by the Langmuir Probe Instrument (LAP). Methods. To identify the effects of flares, we proceeded from an existing flare catalog of Earth-directed solar flares, from which a new list was created that only included Rosetta-directed flares. We also used measurements of flares at Mars when at similar longitudes as Rosetta. The flare irradiance spectral model (FISM v.1) and its Mars equivalent (FISM-M) produce an extreme-ultraviolet (EUV) irradiance (10-120 nm) of the flares at 1 min resolution. LAP data and density measurements obtained with the Mutual Impedence Probe (MIP) from the time of arrival of the flares at Rosetta were examined to determine the flare effects. Results. From the vantage point of Earth, 1504 flares directed toward Rosetta occurred during the mission. In only 24 of these, that is, 1.6%, was the increase in EUV irradiance large enough to cause an observable effect in LAP data. Twenty-four Mars-directed flares were also observed in Rosetta data. The effect of the flares was to increase the photoelectron current by typically 1-5 nA. We find little evidence that the solar flares increase the plasma density, at least not above the background variability. Conclusions. Solar flares have a small effect on the photoelectron current of the LAP instrument, and they are not significant in comparison to other factors that control the plasma density in the coma. The photoelectron current can only be used for flare detection during periods of calm plasma conditions.

  • 27.
    Edberg, Niklas J. T.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Fredrik L.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Henri, P.
    CNRS, Lab Phys & Chim Environm & Espace, Orleans, France.;UCA, Lab Lagrange, OCA, CNRS, Nice, France..
    De Keyser, J.
    BIRA IASB, Royal Belgian Inst Space Aeron, Brussels, Belgium..
    Radial distribution of plasma at comet 67P: Implications for cometary flyby missions2022In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 663, article id A42Article in journal (Refereed)
    Abstract [en]

    Context. The Rosetta spacecraft followed comet 67P/Churyumov-Gerasimenko (67P) for more than two years at a slow walking pace (similar to 1 m s(-1)) within 1500 km from the nucleus. During one of the radial movements of the spacecraft in the early phase of the mission, the radial distribution of the plasma density could be estimated, and the ionospheric density was found to be inversely proportional to the cometocentric distance r from the nucleus (a 1/r distribution). Aims. This study aims to further characterise the radial distribution of plasma around 67P throughout the mission and to expand on the initial results. We also aim to investigate how a 1/r distribution would be observed during a flyby with a fast (similar to 10's km s(-1)) spacecraft, such as the upcoming Comet Interceptor mission, when there is also an asymmetry introduced to the outgassing over the comet surface. Methods. To determine the radial distribution of the plasma, we used data from the Langmuir probe and Mutual Impedance instruments from the Rosetta Plasma Consortium during six intervals throughout the mission, for which the motion of Rosetta was approximately radial with respect to the comet. We then simulated what distribution a fast flyby mission would actually observe during its passage through a coma when there is a 1/r plasma density distribution as well as a sinusoidal variation with a phase angle (and then a sawtooth variation) multiplied to the outgassing rate. Results. The plasma density around comet 67P is found to roughly follow a 1/r dependence, although significant deviations occur in some intervals. If we normalise all data to a common outgassing rate (or heliocentric distance) and combine the intervals to a radial range of 10-1500 km, we find a 1/r(1.19) average distribution. The simulated observed density from a fast spacecraft flying through a coma with a 1/r distribution and an asymmetric outgassing can, in fact, appear anywhere in the range from a 1/r distribution to a 1/r(2) distribution, or even slightly outside of this range. Conclusions. The plasma density is distributed in such a way that it approximately decreases in a manner that is inversely proportional to the cometocentric distance. This is to be expected from the photoionisation of a collision-less, expanding neutral gas at a constant ionisation rate and expansion speed. The deviation from a pure 1/r distribution is in many cases caused by asymmetric outgassing over the surface, additional ionisation sources being present, electric fields accelerating plasma, and changing upstream solar wind conditions. A fast flyby mission can observe a radial distribution that deviates significantly from a 1/r trend if the outgassing is not symmetric over the surface. The altitude profile that will be observed depends very much on the level of outgassing asymmetry, the flyby velocity, the comet rotation rate, and the rotation phase. It is therefore essential to include data from both the inbound and outbound legs, as well as to compare plasma density to neutral density to get a more complete understanding of the radial distribution of the plasma.

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  • 28.
    Engelhardt, Ilka. A. D.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Valliéres, X.
    Rubin, M.
    Gilet, N.
    Henri, P.
    Cold electrons at comet 67P/Churyumov-Gerasimenko2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 616, article id A51Article in journal (Refereed)
    Abstract [en]

    Context. The electron temperature of the plasma is one important aspect of the environment. Electrons created by photoionization or impact ionization of atmospheric gas have energies ∼10 eV. In an active comet coma the gas density is high enough for rapid cooling of the electron gas to the neutral gas temperature (few hundred kelvin). How cooling evolves in less active comets has not been studied before.

    Aims. To investigate how electron cooling varied as comet 67P/Churyumov-Gerasimenko changed its activity by three orders of magnitude during the Rosetta mission.

    Methods. We use in-situ data from Rosetta plasma and neutral gas sensors. By combining Langmuir probe bias voltage sweeps and Mutual Impedance Probe measurements we determine when cold electrons form at least 25% of the total electron density. We compare the results to what is expected from simple models of electron cooling, using the observed neutral gas density as input.

    Results. We demonstrate that the slope of the Langmuir probe sweep can be used as a proxy for cold electron presence. We show statistics of cold electron observations over the 2 year mission period. We find cold electrons at lower activity than expected by a simple model based on free radial expansion and continuous loss of electron energy. Cold electrons are seen mainly when the gas density indicates an exobase may have formed.

    Conclusions. Collisional cooling of electrons following a radial outward path is not sufficient for explaining the observations. We suggest the ambipolar electric field is important for the observed cooling. This field keeps electrons in the inner coma for much longer time, giving them time to dissipate energy by collisions with the neutrals. We conclude there is need of better models to describe the plasma environment of comets, including at least two populations of electrons and the ambipolar field.

  • 29.
    Engelhardt, Ilka. A. D.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Stenberg Wieser, G.
    Goetz, C.
    Rubin, M.
    Henri, P.
    Nilsson, H.
    Odelstad, Elias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Hajra, R.
    Valliéres, X.
    Plasma Density Structures at Comet 67P/Churyumov-Gerasimenko2018In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 477, no 1, p. 1296-1307Article in journal (Refereed)
    Abstract [en]

    We present Rosetta RPC case study from four events at various radial distance, phase angle and local time from autumn 2015, just after perihelion of comet 67P/Churyumov-Gerasimenko. Pulse like (high amplitude, up to minutes in time) signatures are seen with several RPC instruments in the plasma density (LAP, MIP), ion energy and flux (ICA) as well as magnetic field intensity (MAG). Furthermore the cometocentric distance relative to the electron exobase is seen to be a good organizing parameter for the measured plasma variations. The closer Rosetta is to this boundary, the more pulses are measured. This is consistent with the pulses being filaments of plasma originating from the diamagnetic cavity boundary as predicted by simulations. 

  • 30.
    Engelhardt, Ilka. A. D.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Wahlund, Jan -Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Andrews, David J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders. I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Ye, S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Kurth, W. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Gurnett, D. A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Morooka, M. W.
    Univ Colorado, Atmospher & Space Phys Lab, Boulder, CO 80303 USA..
    Farrell, W. M.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Dougherty, M. K.
    Univ London Imperial Coll Sci Technol & Med, Blackett Lab, London SW7 2BZ, England..
    Plasma regions, charged dust and field-aligned currents near Enceladus2015In: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 117, p. 453-469Article in journal (Refereed)
    Abstract [en]

    We use data from several instruments on board Cassini to determine the characteristics of the plasma and dust regions around Saturn's moon Enceladus. For this we utilize the Langmuir probe and the electric antenna connected to the wideband receiver of the radio and plasma wave science (RPWS) instrument package as well as the magnetometer (MAG). We show that there are several distinct plasma and dust regions around Enceladus. Specifically they are the plume filled with neutral gas, plasma, and charged dust, with a distinct edge boundary region. Here we present observations of a new distinct plasma region, being a dust trail on the downstream side. This is seen both as a difference in ion and electron densities, indicating the presence of charged dust, and directly from the signals created on RPWS antennas by the dust impacts on the spacecraft. Furthermore, we show a very good scaling of these two independent dust density measurement methods over four orders of magnitude in dust density, thereby for the first time cross-validating them. To establish equilibrium with the surrounding plasma the dust becomes negatively charged by attracting free electrons. The dust distribution follows a simple power law and the smallest dust particles in the dust trail region are found to be 10 nm in size as well as in the edge region around the plume. Inside the plume the presence of even smaller particles of about 1 nm is inferred. From the magnetic field measurements we infer strong field-aligned currents at the geometrical edge of Enceladus.

  • 31.
    Engwall, Erik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Cully, Christopher M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Puhl-Quinn, Pamela
    Space Science Center, University of New Hampshire, Durham, New Hampshire 03824-3525, USA.
    Vaith, Hans
    Space Science Center, University of New Hampshire, Durham, New Hampshire 03824-3525, USA.
    Torbert, Roy
    Space Science Center, University of New Hampshire, Durham, New Hampshire 03824-3525, USA.
    Survey of cold ionospheric outflows in the magnetotail2009In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 27, no 8, p. 3185-3201Article in journal (Refereed)
    Abstract [en]

    Low-energy ions escape from the ionosphere and constitute a large part of the magnetospheric content, especially in the geomagnetic tail lobes. However, they are normally invisible to spacecraft measurements, since the potential of a sunlit spacecraft in a tenuous plasma in many cases exceeds the energy-per-charge of the ions, and little is therefore known about their outflow properties far from the Earth. Here we present an extensive statistical study of cold ion outflows (0-60 eV) in the geomagnetic tail at geocentric distances from 5 to 19 R-E using the Cluster spacecraft during the period from 2001 to 2005. Our results were obtained by a new method, relying on the detection of a wake behind the spacecraft. We show that the cold ions dominate in both flux and density in large regions of the magnetosphere. Most of the cold ions are found to escape from the Earth, which improves previous estimates of the global outflow. The local outflow in the magnetotail corresponds to a global outflow of the order of 10(26) ions s(-1). The size of the outflow depends on different solar and magnetic activity levels.

  • 32.
    Ergun, R. E.
    et al.
    Univ Colorado, Dept Astrophys & Planetary Sci, Boulder, CO 80309 USA.;Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA..
    Andersson, L. A.
    Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA..
    Fowler, C. M.
    Univ Colorado, Dept Astrophys & Planetary Sci, Boulder, CO 80309 USA.;Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA..
    Woodson, A. K.
    Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA..
    Weber, T. D.
    Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA..
    Delory, G. T.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Andrews, David J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    McEnulty, T.
    Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA..
    Morooka, M. W.
    Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA..
    Stewart, A. I. F.
    Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA..
    Mahaffy, P. R.
    NASA, Goddard Space Flight Ctr, Planetary Environm Lab, Code 699, Greenbelt, MD USA..
    Jakosky, B. M.
    Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA..
    Enhanced O-2(+) loss at Mars due to an ambipolar electric field from electron heating2016In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, no 5, p. 4668-4678Article in journal (Refereed)
    Abstract [en]

    Recent results from the MAVEN Langmuir Probe and Waves instrument suggest higher than predicted electron temperatures (T-e) in Mars' dayside ionosphere above similar to 180km in altitude. Correspondingly, measurements from Neutral Gas and Ion Mass Spectrometer indicate significant abundances of O-2(+) up to similar to 500km in altitude, suggesting that O-2(+) may be a principal ion loss mechanism of oxygen. In this article, we investigate the effects of the higher T-e (which results from electron heating) and ion heating on ion outflow and loss. Numerical solutions show that plasma processes including ion heating and higher T-e may greatly increase O-2(+) loss at Mars. In particular, enhanced T-e in Mars' ionosphere just above the exobase creates a substantial ambipolar electric field with a potential (e) of several k(B)T(e), which draws ions out of the region allowing for enhanced escape. With active solar wind, electron, and ion heating, direct O-2(+) loss could match or exceed loss via dissociative recombination of O-2(+). These results suggest that direct loss of O-2(+) may have played a significant role in the loss of oxygen at Mars over time.

  • 33.
    Ergun, R. E.
    et al.
    Univ Colorado, Dept Astrophys & Planetary Sci, Boulder, CO 80309 USA.;Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA..
    Morooka, M. W.
    Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA..
    Andersson, L. A.
    Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA..
    Fowler, C. M.
    Univ Colorado, Dept Astrophys & Planetary Sci, Boulder, CO 80309 USA.;Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA..
    Delory, G. T.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Andrews, David J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    McEnulty, T.
    Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA..
    Jakosky, B. M.
    Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA..
    Dayside electron temperature and density profiles at Mars: First results from the MAVEN Langmuir probe and waves instrument2015In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 21, p. 8846-8853Article in journal (Refereed)
    Abstract [en]

    We present Mars' electron temperature (T-e) and density (n(e)) altitude profiles derived from the MAVEN (Mars Atmosphere and Volatile EvolutioN) mission deep dip orbits in April 2015, as measured by the Langmuir probe instrument. These orbits had periapsides below 130 km in altitude at low solar zenith angles. The periapsides were above the peak in n(e) during this period. Using a Chapman function fit, we find that scale height and projected altitude of the n(e) peak are consistent with models and previous measurements. The peak electron density is slightly higher than earlier works. For the first time, we present in situ measurements of T-e altitude profiles in Mars' dayside in the altitude range from similar to 130 km to 500 km and provide a functional fit. Importantly, T-e rises rapidly with altitude from similar to 180 km to similar to 300 km. These results and functional fit are important for modeling Mars' ionosphere and understanding atmospheric escape.

  • 34.
    Eriksson, Anders
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Engwall, Erik
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Prakash, R.
    Daldorff, Lars
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Torbert, R.
    Making use of spacecraft-plasma interactions: determining tenous plasma winds from wake observations and numerical simulations2007In: Proceedings of the 10th Spacecraft Charging Technology Conference, 2007Conference paper (Other scientific)
  • 35.
    Eriksson, Anders I.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Engelhardt, Ilka. A. D.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Boström, Rolf
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Edberg, Niklas J. T.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Fredrik L.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Odelstad, Elias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Henri, P.
    LPC2E, Lab Phys & Chim Environm & Espace.
    Lebreton, J. -P
    LPC2E, Lab Phys & Chim Environm & Espace.
    Miloch, W. J.
    Univ Oslo, Dept Phys.
    Paulsson, J. J. P.
    Univ Oslo, Dept Phys.
    Wedlund, Cyril Simon
    Univ Oslo, Dept Phys.
    Yang, L.
    Univ Oslo, Dept Phys.
    Karlsson, T.
    Royal Inst Technol, Alfvén Lab.
    Jarvinen, R.
    Finnish Meteorol Inst, Helsinki 00560.
    Broiles, Thomas
    Southwest Res Inst, San Antonio.
    Mandt, K.
    Southwest Res Inst, San Antonio; Univ Texas San Antonio, Dept Phys & Astron.
    Carr, C. M.
    Imperial Coll London, Dept Phys.
    Galand, M.
    Imperial Coll London, Dept Phys.
    Nilsson, H.
    Swedish Inst Space Phys, S-98128 Kiruna.
    Norberg, C.
    Swedish Inst Space Phys, S-98128 Kiruna.
    Cold and warm electrons at comet 67P/Churyumov-Gerasimenko2017In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 605, article id A15Article in journal (Refereed)
    Abstract [en]

    Context. Strong electron cooling on the neutral gas in cometary comae has been predicted for a long time, but actual measurements of low electron temperature are scarce. Aims. Our aim is to demonstrate the existence of cold electrons in the inner coma of comet 67P/Churyumov-Gerasimenko and show filamentation of this plasma.

    Methods. In situ measurements of plasma density, electron temperature and spacecraft potential were carried out by the Rosetta Langmuir probe instrument, LAP. We also performed analytical modelling of the expanding two-temperature electron gas.

    Results. LAP data acquired within a few hundred km from the nucleus are dominated by a warm component with electron temperature typically 5-10 eV at all heliocentric distances covered (1.25 to 3.83 AU). A cold component, with temperature no higher than about 0.1 eV, appears in the data as short (few to few tens of seconds) pulses of high probe current, indicating local enhancement of plasma density as well as a decrease in electron temperature. These pulses first appeared around 3 AU and were seen for longer periods close to perihelion. The general pattern of pulse appearance follows that of neutral gas and plasma density. We have not identified any periods with only cold electrons present. The electron flux to Rosetta was always dominated by higher energies, driving the spacecraft potential to order -10 V.

    Conclusions. The warm (5-10 eV) electron population observed throughout the mission is interpreted as electrons retaining the energy they obtained when released in the ionisation process. The sometimes observed cold populations with electron temperatures below 0.1 eV verify collisional cooling in the coma. The cold electrons were only observed together with the warm population. The general appearance of the cold population appears to be consistent with a Haser-like model, implicitly supporting also the coupling of ions to the neutral gas. The expanding cold plasma is unstable, forming filaments that we observe as pulses.

  • 36.
    Eriksson, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Sjöqvist, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Monopole Field Textures in Interacting Spin Systems2020In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 101, no 5Article in journal (Refereed)
    Abstract [en]

    Magnetic monopoles can appear as emergent structures in a wide range of physical settings, ranging from spin ice to Weyl points in semimetals. Here, a distribution of synthetic (Berry) monopoles in parameter space of a slowly changing external magnetic field is demonstrated in a system of interacting spin-1/2 particles with broken spherical symmetry. These monopoles can be found at points where the external field is nonzero. The spin-spin interaction provides a mechanism for splitting the synthetic local magnetic charges until their magnitude reach the smallest allowed value 1/2. For certain states, a nonzero net charge can be created in an arbitrarily large finite region of parameter space. The monopole field textures contain non-monopolar contributions in the presence of spin-spin interaction.

  • 37.
    Fowler, C. M.
    et al.
    Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA..
    Andersson, L.
    Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA..
    Ergun, R. E.
    Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA..
    Morooka, M.
    Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA..
    Delory, G.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Andrews, David J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Lillis, Robert J.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    McEnulty, T.
    Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA..
    Weber, T. D.
    Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA..
    Chamandy, T. M.
    Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA..
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Mitchell, D. L.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Mazelle, C.
    Inst Rech Astrophys & Planetol, CNRS, Toulouse, France.;Univ Toulouse 3, Inst Rech Astrophys & Planetol, F-31062 Toulouse, France..
    Jakosky, B. M.
    Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA..
    The first in situ electron temperature and density measurements of the Martian nightside ionosphere2015In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 21, p. 8854-8861Article in journal (Refereed)
    Abstract [en]

    The first in situ nightside electron density and temperature profiles at Mars are presented as functions of altitude and local time (LT) from the Langmuir Probe and Waves (LPW) instrument on board the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission spacecraft. LPW is able to measure densities as low as similar to 100 cm(-3), a factor of up to 10 or greater improvement over previous measurements. Above 200 km, near-vertical density profiles of a few hundred cubic centimeters were observed for almost all nightside LT, with the lowest densities and highest temperatures observed postmidnight. Density peaks of a few thousand cubic centimeters were observed below 200 km at all nightside LT. The lowest temperatures were observed below 180 km and approach the neutral atmospheric temperature. One-dimensional modeling demonstrates that precipitating electrons were able to sustain the observed nightside ionospheric densities below 200 km.

  • 38.
    Galand, M.
    et al.
    Imperial Coll London, Dept Phys, London, England..
    Feldman, P. D.
    Johns Hopkins Univ, Dept Phys & Astron, Baltimore, MD 21218 USA..
    Bockelee-Morvan, D.
    Univ Paris, Sorbonne Univ, Univ PSL, CNRS,Observ Paris,LESIA, Meudon, France..
    Biver, N.
    Univ Paris, Sorbonne Univ, Univ PSL, CNRS,Observ Paris,LESIA, Meudon, France..
    Cheng, Y. -C
    Rinaldi, G.
    INAF, IAPS, Rome, Italy..
    Rubin, M.
    Univ Bern, Phys Inst, Bern, Switzerland..
    Altwegg, K.
    Univ Bern, Phys Inst, Bern, Switzerland..
    Deca, J.
    Univ Colorado, Lab Atmospher & Space Phys LASP, Boulder, CO 80309 USA.;NASA, Inst Modeling Plasma Atmospheres & Cosm Dust, SSERVI, Moffett Field, CA USA..
    Beth, A.
    Imperial Coll London, Dept Phys, London, England..
    Stephenson, P.
    Imperial Coll London, Dept Phys, London, England..
    Heritier, K. L.
    Imperial Coll London, Dept Phys, London, England..
    Henri, P.
    Univ Orleans, CNRS, LPC2E, Orleans, France..
    Parker, J. Wm.
    Southwest Res Inst, Dept Space Studies, Boulder, CO USA..
    Carr, C.
    Imperial Coll London, Dept Phys, London, England..
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Burch, J.
    Southwest Res Inst, San Antonio, TX USA..
    Far-ultraviolet aurora identified at comet 67P/Churyumov-Gerasimenko2020In: Nature Astronomy, E-ISSN 2397-3366, Vol. 4, no 11, p. 1084-1091Article in journal (Refereed)
    Abstract [en]

    In situ measurements from the Rosetta spacecraft reveal the presence of atomic emissions close to comet 67P's nucleus. Such emissions are due to dissociative excitation of molecules by the interaction with the solar wind, identifying them as a form of aurora. Having a nucleus darker than charcoal, comets are usually detected from Earth through the emissions from their coma. The coma is an envelope of gas that forms through the sublimation of ices from the nucleus as the comet gets closer to the Sun. In the far-ultraviolet portion of the spectrum, observations of comae have revealed the presence of atomic hydrogen and oxygen emissions. When observed over large spatial scales as seen from Earth, such emissions are dominated by resonance fluorescence pumped by solar radiation. Here, we analyse atomic emissions acquired close to the cometary nucleus by the Rosetta spacecraft and reveal their auroral nature. To identify their origin, we undertake a quantitative multi-instrument analysis of these emissions by combining coincident neutral gas, electron and far-ultraviolet observations. We establish that the atomic emissions detected from Rosetta around comet 67P/Churyumov-Gerasimenko at large heliocentric distances result from the dissociative excitation of cometary molecules by accelerated solar-wind electrons (and not by electrons produced from photo-ionization of cometary molecules). Like the discrete aurorae at Earth and Mars, this cometary aurora is driven by the interaction of the solar wind with the local environment. We also highlight how the oxygen line Oiat wavelength 1,356 A could be used as a tracer of solar-wind electron variability.

  • 39.
    Galand, M.
    et al.
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England..
    Heritier, K. L.
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England..
    Odelstad, Elias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Henri, P.
    Univ Orleans, CNRS, LPC2E, 3A,Ave Rech Sci, F-45071 Orleans 2, France..
    Broiles, T. W.
    Southwest Res Inst, PO Drawer 28510, San Antonio, TX 78228 USA..
    Allen, A. J.
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England..
    Altwegg, K.
    Univ Bern, Phys Inst, Sidlerstr 5, CH-3012 Bern, Switzerland..
    Beth, A.
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England..
    Burch, J. L.
    Southwest Res Inst, PO Drawer 28510, San Antonio, TX 78228 USA..
    Carr, C. M.
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England..
    Cupido, E.
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England..
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Glassmeier, K. -H
    Johansson, Fredrik L.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Lebreton, J. -P
    Mandt, K. E.
    Southwest Res Inst, PO Drawer 28510, San Antonio, TX 78228 USA..
    Nilsson, H.
    Swedish Inst Space Phys, POB 812, SE-98128 Kiruna, Sweden..
    Richter, I.
    TU Braunschweig, Inst Geophys & Extraterr Phys, Mendelssohnstr 3, D-38106 Braunschweig, Germany..
    Rubin, M.
    Univ Bern, Phys Inst, Sidlerstr 5, CH-3012 Bern, Switzerland..
    Sagnieres, L. B. M.
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England..
    Schwartz, S. J.
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England..
    Semon, T.
    Univ Bern, Phys Inst, Sidlerstr 5, CH-3012 Bern, Switzerland..
    Tzou, C. -Y
    Vallieres, X.
    Univ Orleans, CNRS, LPC2E, 3A,Ave Rech Sci, F-45071 Orleans 2, France..
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wurz, P.
    Univ Bern, Phys Inst, Sidlerstr 5, CH-3012 Bern, Switzerland..
    Ionospheric plasma of comet 67P probed by Rosetta at 3 au from the Sun2016In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 462, p. S331-S351Article in journal (Refereed)
    Abstract [en]

    We propose to identify the main sources of ionization of the plasma in the coma of comet 67P/Churyumov-Gerasimenko at different locations in the coma and to quantify their relative importance, for the first time, for close cometocentric distances (< 20 km) and large heliocentric distances (> 3 au). The ionospheric model proposed is used as an organizing element of a multi-instrument data set from the Rosetta Plasma Consortium (RPC) plasma and particle sensors, from the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis and from the Microwave Instrument on the Rosetta Orbiter, all on board the ESA/Rosetta spacecraft. The calculated ionospheric density driven by Rosetta observations is compared to the RPC-Langmuir Probe and RPC-Mutual Impedance Probe electron density. The main cometary plasma sources identified are photoionization of solar extreme ultraviolet (EUV) radiation and energetic electron-impact ionization. Over the northern, summer hemisphere, the solar EUV radiation is found to drive the electron density - with occasional periods when energetic electrons are also significant. Over the southern, winter hemisphere, photoionization alone cannot explain the observed electron density, which reaches sometimes higher values than over the summer hemisphere; electron-impact ionization has to be taken into account. The bulk of the electron population is warm with temperature of the order of 7-10 eV. For increased neutral densities, we show evidence of partial energy degradation of the hot electron energy tail and cooling of the full electron population.

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  • 40. Garnier, P.
    et al.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Holmberg, Madeleine K. G.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Morooka, M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Grimald, S.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Schippers, P.
    Gurnett, D. A.
    Krimigis, S. M.
    Krupp, N.
    Coates, A.
    Crary, F.
    Gustafsson, Georg
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    The detection of energetic electrons with the Cassini Langmuir probe at Saturn2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, p. A10202-Article in journal (Refereed)
    Abstract [en]

    The Cassini Langmuir probe, part of the Radio and Plasma Wave Science (RPWS) instrument, has provided a wealth of information about the cold and dense plasma in the Saturnian system. The analysis of the ion side current (current for negative potentials) measured by the probe from 2005 to 2008 reveals also a strong sensitivity to energetic electrons (250-450 eV). These electrons impact the surface of the probe, and generate a detectable current of secondary electrons. A broad secondary electrons current region is inferred from the observations in the dipole L Shell range of similar to 6-10, with a peak full width at half maximum (FWHM) at L = 6.4-9.4 (near the Dione and Rhea magnetic dipole L Shell values). This magnetospheric flux tube region, which displays a large day/night asymmetry, is related to the similar structure in the energetic electron fluxes as the one measured by the onboard Electron Spectrometer (ELS) of the Cassini Plasma Spectrometer (CAPS). It corresponds spatially to both the outer electron radiation belt observed by the Magnetosphere Imaging Instrument (MIMI) at high energies and to the low-energy peak which has been observed since the Voyager era. Finally, a case study suggests that the mapping of the current measured by the Langmuir probe for negative potentials can allow to identify the plasmapause-like boundary recently identified at Saturn, and thus potentially identify the separation between the closed and open magnetic field lines regions.

  • 41.
    Gilet, N.
    et al.
    Univ Orleans, Lab Phys & Chim Environm & Espace LPC2E, CNRS, Orleans, France..
    Henri, P.
    Univ Orleans, Lab Phys & Chim Environm & Espace LPC2E, CNRS, Orleans, France.;Lab Lagrange, CNRS, UCA, OCA, Nice, France..
    Wattieaux, G.
    Univ Toulouse, LAPLACE UMR 5213, F-31062 Toulouse, France..
    Traore, N.
    Univ Orleans, Lab Phys & Chim Environm & Espace LPC2E, CNRS, Orleans, France..
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vallieres, X.
    Univ Orleans, Lab Phys & Chim Environm & Espace LPC2E, CNRS, Orleans, France..
    More, J.
    Univ Orleans, Lab Phys & Chim Environm & Espace LPC2E, CNRS, Orleans, France..
    Randriamboarison, O.
    Univ Orleans, Lab Phys & Chim Environm & Espace LPC2E, CNRS, Orleans, France..
    Odelstad, Elias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Swedish Inst Space Phys, Box 537, S-75121 Uppsala, Sweden.;Uppsala Univ, Dept Phys & Astron, Box 516, S-75210 Uppsala, Sweden..
    Rubin, M.
    Univ Bern, Phys Inst, Sidelerstr 5, CH-3012 Bern, Switzerland..
    Observations of a mix of cold and warm electrons by RPC-MIP at 67P/Churyumov-Gerasimenko2020In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 640, article id A110Article in journal (Refereed)
    Abstract [en]

    Context. The Mutual Impedance Probe (MIP) of the Rosetta Plasma Consortium (RPC) onboard the Rosetta orbiter which was in operation for more than two years, between August 2014 and September 2016 to monitor the electron density in the cometary ionosphere of 67P/Churyumov-Gerasimenko. Based on the resonance principle of the plasma eigenmodes, recent models of the mutual impedance experiment have shown that in a two-electron temperature plasma, such an instrument is able to separate the two isotropic electron populations and retrieve their properties.Aims. The goal of this paper is to identify and characterize regions of the cometary ionized environment filled with a mix of cold and warm electron populations, which was observed by Rosetta during the cometary operation phase.Methods. To reach this goal, this study identifies and investigates the in situ mutual impedance spectra dataset of the RPC-MIP instrument that contains the characteristics of a mix of cold and warm electrons, with a special focus on instrumental signatures typical of large cold-to-total electron density ratio (from 60 to 90%), that is, regions strongly dominated by the cold electron component.Results. We show from the observational signatures that the mix of cold and warm cometary electrons strongly depends on the cometary latitude. Indeed, in the southern hemisphere of 67P, where the neutral outgassing activity was higher than in northern hemisphere during post-perihelion, the cold electrons were more abundant, confirming the role of electron-neutral collisions in the cooling of cometary electrons. We also show that the cold electrons are mainly observed outside the nominal electron-neutral collision-dominated region (exobase), where electrons are expected to have cooled down. This which indicates that the cold electrons have been transported outward. Finally, RPC-MIP detected cold electrons far from the perihelion, where the neutral outgassing activity is lower, in regions where no electron exobase was expected to have formed. This suggests that the cometary neutrals provide a more frequent or efficient cooling of the electrons than expected for a radially expanding ionosphere.

  • 42.
    Goetz, C.
    et al.
    TU Braunschweig, Inst Geophys & Extraterr Phys, Mendelssohnstr 3, D-38106 Braunschweig, Germany..
    Koenders, C.
    TU Braunschweig, Inst Geophys & Extraterr Phys, Mendelssohnstr 3, D-38106 Braunschweig, Germany..
    Hansen, K. C.
    Univ Michigan, Dept Atmospher Ocean & Space Sci, 2455 Hayward St, Ann Arbor, MI 48109 USA..
    Burch, J.
    Southwest Res Inst, PO Drawer 28510, San Antonio, TX 78228 USA..
    Carr, C.
    Imperial Coll London, Space & Atmospher Phys Grp, Exhibit Rd, London SW7 2AZ, England..
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Fruehauff, D.
    TU Braunschweig, Inst Geophys & Extraterr Phys, Mendelssohnstr 3, D-38106 Braunschweig, Germany..
    Guettler, C.
    Max Planck Inst Sonnensyst Forschung, Justus von Liebig Weg 3, D-37077 Gottingen, Germany..
    Henri, P.
    Univ Orleans, CNRS, UMR 7328, Lab Phys & Chim Environm & Espace, F-45100 Orleans, France..
    Nilsson, H.
    Swedish Inst Space Phys, POB 812, SE-98128 Kiruna, Sweden..
    Richter, I.
    TU Braunschweig, Inst Geophys & Extraterr Phys, Mendelssohnstr 3, D-38106 Braunschweig, Germany..
    Rubin, M.
    Univ Bern, Phys Inst, Sidlerstr 5, CH-3012 Bern, Switzerland..
    Sierks, H.
    Max Planck Inst Sonnensyst Forschung, Justus von Liebig Weg 3, D-37077 Gottingen, Germany..
    Tsurutani, B.
    CALTECH, Jet Prop Lab, 4800 Oak Grove Dr, Pasadena, CA 91109 USA..
    Volwerk, M.
    Austrian Acad Sci, Inst Weltraumforsch, Schmiedlstr 6, A-8042 Graz, Austria..
    Glassmeier, K. H.
    TU Braunschweig, Inst Geophys & Extraterr Phys, Mendelssohnstr 3, D-38106 Braunschweig, Germany.;Max Planck Inst Sonnensyst Forschung, Justus von Liebig Weg 3, D-37077 Gottingen, Germany..
    Structure and evolution of the diamagnetic cavity at comet 67P/Churyumov-Gerasimenko2016In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 462, p. S459-S467Article in journal (Refereed)
    Abstract [en]

    The long duration of the Rosetta mission allows us to study the evolution of the diamagnetic cavity at comet 67P/Churyumov-Gerasimenko in detail. From 2015 April to 2016 February 665 intervals could be identified where Rosetta was located in a zero-magnetic-field region. We study the temporal and spatial distribution of this cavity and its boundary and conclude that the cavity properties depend on the long-term trend of the outgassing rate, but do not respond to transient events at the spacecraft location, such as outbursts or high neutral densities. Using an empirical model of the outgassing rate, we find a functional relationship between the outgassing rate and the distance of the cavity to the nucleus. There is also no indication that this unexpectedly large distance is related to unusual solar wind conditions. Because the deduced shape of the cavity boundary is roughly elliptical on small scales and the distances of the boundary from the nucleus are much larger than expected we conclude that the events observed by Rosetta are due to a moving instability of the cavity boundary itself.

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  • 43.
    Goetz, C.
    et al.
    Tech Univ Carolo Wilhelmina Braunschweig, Inst Geophys & Extraterr Phys, Mendelssohnstr 3, D-38106 Braunschweig, Germany..
    Koenders, C.
    Tech Univ Carolo Wilhelmina Braunschweig, Inst Geophys & Extraterr Phys, Mendelssohnstr 3, D-38106 Braunschweig, Germany..
    Richter, I.
    Tech Univ Carolo Wilhelmina Braunschweig, Inst Geophys & Extraterr Phys, Mendelssohnstr 3, D-38106 Braunschweig, Germany..
    Altwegg, K.
    Univ Bern, Phys Inst, Sidlerstr 5, CH-3012 Bern, Switzerland..
    Burch, J.
    Southwest Res Inst, PO Drawer 28510, San Antonio, TX 78228 USA..
    Carr, C.
    Univ London Imperial Coll Sci Technol & Med, Space & Atmospher Phys Grp, Exhibit Rd, London SW7 2AZ, England..
    Cupido, E.
    Univ London Imperial Coll Sci Technol & Med, Space & Atmospher Phys Grp, Exhibit Rd, London SW7 2AZ, England..
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Guettler, C.
    Max Planck Inst Sonnensyst Forsch, Justus von Liebig Weg 3, D-37077 Gottingen, Germany..
    Henri, P.
    Univ Orleans, CNRS, Lab Phys & Chim Environm & Espace, UMR 7328, F-45100 Orleans, France..
    Mokashi, P.
    Southwest Res Inst, PO Drawer 28510, San Antonio, TX 78228 USA..
    Nemeth, Z.
    Wigner Res Ctr Phys, Konkoly Thege Miklos Ut 29-33, H-1121 Budapest, Hungary..
    Nilsson, H.
    Swedish Inst Space Phys, POB 812, S-98128 Kiruna, Sweden..
    Rubin, M.
    Univ Bern, Phys Inst, Sidlerstr 5, CH-3012 Bern, Switzerland..
    Sierks, H.
    Max Planck Inst Sonnensyst Forsch, Justus von Liebig Weg 3, D-37077 Gottingen, Germany..
    Tsurutani, B.
    CALTECH, Jet Prop Lab, 4800 Oak Grove Dr, Pasadena, CA 91109 USA..
    Vallat, C.
    European Space Astron Ctr, Madrid 28691, Spain..
    Volwerk, M.
    Austrian Acad Sci, Space Res Inst, Schmiedlstr 6, A-8042 Graz, Austria..
    Glassmeier, K. -H
    First detection of a diamagnetic cavity at comet 67P/Churyumov-Gerasimenko2016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 588, article id A24Article in journal (Refereed)
    Abstract [en]

    Context. The Rosetta magnetometer RPC-MAG has been exploring the plasma environment of comet 67P/Churyumov-Gerasimenko since August 2014. The first months were dominated by low-frequency waves which evolved into more complex features. However, at the end of July 2015, close to perihelion, the magnetometer detected a region that did not contain any magnetic field at all. Aims. These signatures match the appearance of a diamagnetic cavity as was observed at comet 1P/Halley in 1986. The cavity here is more extended than previously predicted by models and features unusual magnetic field configurations, which need to be explained. Methods. The onboard magnetometer data were analyzed in detail and used to estimate the outgassing rate. A minimum variance analysis was used to determine boundary normals. Results. Our analysis of the data acquired by the Rosetta Plasma Consortium instrumentation confirms the existence of a diamagnetic cavity. The size is larger than predicted by simulations, however. One possible explanation are instabilities that are propagating along the cavity boundary and possibly a low magnetic pressure in the solar wind. This conclusion is supported by a change in sign of the Sun-pointing component of the magnetic field. Evidence also indicates that the cavity boundary is moving with variable velocities ranging from 230 500m/s.

  • 44.
    Goetz, C.
    et al.
    Tech Univ Carolo Wilhelmina Braunschweig, Inst Geophys & Extraterr Phys, Mendelssohnstr 3, D-38106 Braunschweig, Germany.
    Tsurutani, B. T.
    Jet Prop Lab, Pasadena, CA USA.
    Henri, P.
    CNRS, LPC2E, Orleans, France.
    Volwerk, M.
    Austrian Acad Sci, Inst Weltraumforsch, Schmiedlstr 6, Graz, Austria.
    Behar, E.
    Swedish Inst Space Phys, POB 812, S-98128 Kiruna, Sweden.
    Edberg, Niklas J. T.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Goldstein, R.
    Southwest Res Inst, PO Drawer 28510, San Antonio, TX 78228 USA.
    Mokashi, P.
    Southwest Res Inst, PO Drawer 28510, San Antonio, TX 78228 USA.
    Nilsson, H.
    Austrian Acad Sci, Inst Weltraumforsch, Schmiedlstr 6, Graz, Austria.
    Richter, I
    Tech Univ Carolo Wilhelmina Braunschweig, Inst Geophys & Extraterr Phys, Mendelssohnstr 3, D-38106 Braunschweig, Germany.
    Wellbrock, A.
    UCL Dept Space & Climate Phys, Mullard Space Sci Lab, Dorking, Surrey, England.
    Glassmeier, K. H.
    Tech Univ Carolo Wilhelmina Braunschweig, Inst Geophys & Extraterr Phys, Mendelssohnstr 3, D-38106 Braunschweig, Germany.
    Unusually high magnetic fields in the coma of 67P/Churyumov-Gerasimenko during its high-activity phase2019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 630, article id A38Article in journal (Refereed)
    Abstract [en]

    Aims: On July 3, 2015, an unprecedented increase in the magnetic field magnitude was measured by the Rosetta spacecraft orbiting comet 67P/Churyumov-Gerasimenko (67P). This increase was accompanied by large variations in magnetic field and ion and electron density and energy. To our knowledge, this unusual event marks the highest magnetic field ever measured in the plasma environment of a comet. Our goal here is to examine possible physical causes for this event, and to explain this reaction of the cometary plasma and magnetic field and its trigger.

    Methods: We used observations from the entire Rosetta Plasma Consortium as well as energetic particle measurements from the Standard Radiation Monitor on board Rosetta to characterize the event. To provide context for the solar wind at the comet, observations at Earth were compared with simulations of the solar wind.

    Results: We find that the unusual behavior of the plasma around 67P is of solar wind origin and is caused by the impact of an interplanetary coronal mass ejection, combined with a corotating interaction region. This causes the magnetic field to pile up and increase by a factor of six to about 300 nT compared to normal values of the enhanced magnetic field at a comet. This increase is only partially accompanied by an increase in plasma density and energy, indicating that the magnetic field is connected to different regions of the coma.

  • 45.
    Goetz, Charlotte
    et al.
    European Space Agcy, Estec, Keplerlaan 1, NL-2201 AZ Noordwijk, Netherlands.;Northumbria Univ, Dept Math Phys & Elect Engn, Newcastle Upon Tyne, Tyne & Wear, England..
    Behar, Etienne
    Swedish Inst Space Phys, Box 812, S-98128 Kiruna, Sweden.;CNRS, UCA, OCA, Lagrange, Nice, France..
    Beth, Arnaud
    Umeå Univ, Dept Phys, S-90187 Umeå, Sweden..
    Bodewits, Dennis
    Auburn Univ, Leach Sci Ctr, Phys Dept, Auburn, AL 36832 USA..
    Bromley, Steve
    Auburn Univ, Leach Sci Ctr, Phys Dept, Auburn, AL 36832 USA..
    Burch, Jim
    Southwest Res Inst, PO Drawer 28510, San Antonio, TX 78228 USA..
    Deca, Jan
    Univ Colorado, Lab Atmospher & Space Phys, 3665 Discovery Dr, Boulder, CO 80303 USA..
    Divin, Andrey
    St Petersburg State Univ, Earth Phys Dept, Ulianovskaya 1, St Petersburg 198504, Russia..
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Feldman, Paul D.
    Johns Hopkins Univ, Dept Phys & Astron, Baltimore, MD 21218 USA..
    Galand, Marina
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England..
    Gunell, Herbert
    Umeå Univ, Dept Phys, S-90187 Umeå, Sweden..
    Henri, Pierre
    CNRS, UCA, OCA, Lagrange, Nice, France.;CNRS, LPC2E, Orleans, France..
    Heritier, Kevin
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England..
    Jones, Geraint H.
    UCL Mullard Space Sci Lab, Dorking RH5 6NT, Surrey, England.;UCL Birkbeck, Ctr Planetary Sci, Gower St, London WC1E 6BT, England..
    Mandt, Kathleen E.
    Johns Hopkins Appl Phys Lab, Laurel, MD 20728 USA..
    Nilsson, Hans
    Swedish Inst Space Phys, Box 812, S-98128 Kiruna, Sweden..
    Noonan, John W.
    Univ Arizona, Lunar & Planetary Lab, Tucson, AZ 85719 USA..
    Odelstad, Elias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Parker, Joel W.
    Southwest Res Inst, Boulder, CO 80302 USA..
    Rubin, Martin
    Univ Bern, Phys Inst, Sidlerstr 5, CH-3012 Bern, Switzerland..
    Wedlund, Cyril Simon
    Austrian Acad Sci, Space Res Inst, Schmiedlstr 6, A-8042 Graz, Austria..
    Stephenson, Peter
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England..
    Taylor, Matthew G. G. T.
    European Space Agcy, Estec, Keplerlaan 1, NL-2201 AZ Noordwijk, Netherlands..
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vines, Sarah K.
    Johns Hopkins Appl Phys Lab, Laurel, MD 20723 USA..
    Volwerk, Martin
    Austrian Acad Sci, Space Res Inst, Schmiedlstr 6, A-8042 Graz, Austria..
    The Plasma Environment of Comet 67P/Churyumov-Gerasimenko2022In: Space Science Reviews, ISSN 0038-6308, E-ISSN 1572-9672, Vol. 218, no 8, article id 65Article, review/survey (Refereed)
    Abstract [en]

    The environment of a comet is a fascinating and unique laboratory to study plasma processes and the formation of structures such as shocks and discontinuities from electron scales to ion scales and above. The European Space Agency's Rosetta mission collected data for more than two years, from the rendezvous with comet 67P/Churyumov-Gerasimenko in August 2014 until the final touch-down of the spacecraft end of September 2016. This escort phase spanned a large arc of the comet's orbit around the Sun, including its perihelion and corresponding to heliocentric distances between 3.8 AU and 1.24 AU. The length of the active mission together with this span in heliocentric and cometocentric distances make the Rosetta data set unique and much richer than sets obtained with previous cometary probes. Here, we review the results from the Rosetta mission that pertain to the plasma environment. We detail all known sources and losses of the plasma and typical processes within it. The findings from in-situ plasma measurements are complemented by remote observations of emissions from the plasma. Overviews of the methods and instruments used in the study are given as well as a short review of the Rosetta mission. The long duration of the Rosetta mission provides the opportunity to better understand how the importance of these processes changes depending on parameters like the outgassing rate and the solar wind conditions. We discuss how the shape and existence of large scale structures depend on these parameters and how the plasma within different regions of the plasma environment can be characterised. We end with a non-exhaustive list of still open questions, as well as suggestions on how to answer them in the future.

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  • 46.
    Goldstein, R.
    et al.
    Southwest Res Inst, San Antonio, TX 78228 USA..
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX 78228 USA..
    Llera, K.
    Southwest Res Inst, San Antonio, TX 78228 USA..
    Altwegg, K.
    Univ Bern, Phys Inst, Bern, Switzerland..
    Rubin, M.
    Univ Bern, Phys Inst, Bern, Switzerland..
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Nilsson, H.
    Swedish Inst Space Phys, Kiruna, Sweden..
    Observations of Modulation of Ion Flux in the Coma of Comet 67P/Churyumov-Gerasimenko2022In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 49, no 11, article id e2022GL098042Article in journal (Refereed)
    Abstract [en]

    On 6-8 June 2015, the Ion and Electron Sensor on board Rosetta observed keV-range water-group pickup ions arriving from the solar direction. Based on magnetic field intensification and variations, the appearance of the ions was likely to have been caused by a coronal mass ejection. During the 3-day period when Rosetta was 200 km from the comet, peak ion energy/charge (E/q) varied over a range from 50 eV to 1 keV in concert with neutral gas density variations caused by the rotation of the comet and its variable solar illumination. Thermal ion densities showed the same variations. The neutral density variations provided a unique opportunity to observe the repeated slowing of the solar wind by mass loading caused by charge exchange between energetic water-group ions and thermal water-group molecules. Such solar wind slowing was observed previously only by flyby missions that provided single events.

  • 47.
    Goldstein, R.
    et al.
    Southwest Res Inst, 6220 Culebra Rd, San Antonio, TX 78238 USA.
    Burch, J. L.
    Southwest Res Inst, 6220 Culebra Rd, San Antonio, TX 78238 USA.
    Llera, K.
    Southwest Res Inst, 6220 Culebra Rd, San Antonio, TX 78238 USA.
    Mokashi, P.
    Southwest Res Inst, 6220 Culebra Rd, San Antonio, TX 78238 USA.
    Nilsson, H.
    Swedish Inst Space Phys, Kiruna, Sweden.
    Dokgo, K.
    Southwest Res Inst, 6220 Culebra Rd, San Antonio, TX 78238 USA.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Odelstad, Elias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Richter, I
    Tech Univ Carolo Wilhelmina Braunschweig, Braunschweig, Germany.
    Electron acceleration at comet 67P/Churyumov-Gerasimenko2019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 630, article id A40Article in journal (Refereed)
    Abstract [en]

    We report the observation by the Ion and Electron Sensor (IES) of energetic (>1 keV) electrons in the plasma environment of comet 67P Churyumov-Gerasimenko (67P). Most of the electrons in the cometary coma are expected to be of solar wind, photoionization, or electron impact origin and are therefore not expected to exceed some hundreds of eV in energy. During the Vega flybys of comet Halley, 1 keV electrons were also observed, and these are explained as having been accelerated by lower hybrid (LH) waves resulting from the two-stream instability involving the solar wind and pickup-ion flows. These waves resonate with the cyclotron motion of the ions and the longitudinal motion of electrons and are on the order of several Hz, at least in the case of 67P. We postulate that the energetic electrons we have observed intermittently during December 2015 through January 2016 are also the result of such a process and that Landau damping causes the acceleration and subsequent abrupt decrease in this energy (also seen at Halley). We show from this study an event on 19 January 2016 when IES simultaneously observed accelerated electrons, solar wind protons, water ions, and LH waves. A dispersion analysis shows that the ion-ion two-stream instability has positive growth rates for such waves during the observation period.

  • 48.
    Goldstein, Raymond
    et al.
    Southwest Res Inst, 6220 Culebra Rd, San Antonio, TX 78238 USA.
    Burch, J. L.
    Southwest Res Inst, 6220 Culebra Rd, San Antonio, TX 78238 USA.
    Mokashi, P.
    Southwest Res Inst, 6220 Culebra Rd, San Antonio, TX 78238 USA.
    Mandt, K.
    Southwest Res Inst, 6220 Culebra Rd, San Antonio, TX 78238 USA.
    Carr, C.
    Imperial Coll, Blackett Lab, London SW7 2AZ, England.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Glassmeier, K. -H
    Henri, P.
    Univ Orleans, CNRS, LPC3E, F-45071 Orleans 2, France.
    Nilsson, H.
    Swedish Inst Space Phys, SE-98128 Kiruna, Sweden.
    Rubin, M.
    Univ Bern, Inst Phys, CH-3012 Bern, Switzerland.
    Tzou, C. -Y
    Two years of solar wind and pickup ion measurements at comet 67P/Churyumov-Gerasimenko2017In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 469, p. S262-S267Article in journal (Refereed)
    Abstract [en]

    The Ion and Electron Sensor (IES) as well as other members of the Rosetta Plasma Consortium (RPC) on board the Rosetta spacecraft (S/C) measured the characteristics of the solar wind almost continuously since its arrival at 67P/Churyumov-Gerasimenko (CG) in 2014 August. An important process at a comet is the so-called pickup process in which a newly ionized atom or molecule begins gyrating about the interplanetary magnetic field, is accelerated in the process and is carried along with the solar wind. Within a month after comet arrival, while Rosetta was < 100 km from CG, we began to observe low-energy (< 20 eV) positive ions. We believe that these are newly formed from cometary neutrals near Rosetta and attracted to the negative S/C potential. These ions were in the early phase of pickup and had not yet reached the energy they would after at least one full gyration about the magnetic field. As CG increased its activity, the flux and energy of the measured pickup ions increased intermittently while the solar wind appeared intermittently as well. By about 2015 end of April, the solar wind had become very faint until it eventually disappeared from the IES field of view. We then began to see ions at the highest energy levels of IES, > 10 keV for a few days and then intermittently through the remainder of the mission, but lower energy (a few keV) pickup ions were also observed. As of 2016 early February, the solar wind reappeared more consistently. We believe that the disappearance of the solar wind in the IES field of view is the result of interaction with the pickup ions and the eventual formation of a cavity that excluded the solar wind.

  • 49.
    Graham, Daniel B.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vaivads, A.
    KTH Royal Inst Technol, Sch Elect Engn & Comp Sci, Div Space & Plasma Phys, S-11428 Stockholm, Sweden..
    Edberg, Niklas J. T.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Erik P. G.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Sorriso-Valvo, Luca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Maksimovic, M.
    Univ Paris Diderot, Sorbonne Univ, LESIA, Sorbonne Paris Cite,Observ Paris,Univ PSL,CNRS, 5 Pl Jules Janssen, F-92195 Meudon, France..
    Soucek, J.
    Czech Acad Sci, Inst Atmospher Phys, Prague, Czech Republic..
    Pisa, D.
    Czech Acad Sci, Inst Atmospher Phys, Prague, Czech Republic..
    Bale, S. D.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA.;Univ Calif Berkeley, Dept Phys, Berkeley, CA 94720 USA..
    Chust, T.
    Univ Paris Saclay, LPP, CNRS, Ecole Polytech,Sorbonne Univ,Observ Paris, Paris, France..
    Kretzschmar, M.
    CNRS, LPC2E, 3A Ave Rech Sci, Orleans, France.;Univ Orleans, Orleans, France..
    Krasnoselskikh, V
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA.;CNRS, LPC2E, 3A Ave Rech Sci, Orleans, France..
    Lorfevre, E.
    CNES, 18 Ave Edouard Belin, F-31400 Toulouse, France..
    Plettemeier, D.
    Tech Univ Dresden, Helmholtz Str 10, D-01187 Dresden, Germany..
    Steller, M.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Stverak, S.
    Czech Acad Sci, Astron Inst, Prague, Czech Republic..
    Travnicek, P.
    Czech Acad Sci, Inst Atmospher Phys, Prague, Czech Republic.;Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Vecchio, A.
    Univ Paris Diderot, Sorbonne Univ, LESIA, Sorbonne Paris Cite,Observ Paris,Univ PSL,CNRS, 5 Pl Jules Janssen, F-92195 Meudon, France.;Radboud Univ Nijmegen, Dept Astrophys, Radboud Radio Lab, Nijmegen, Netherlands..
    Horbury, T. S.
    Imperial Coll London, South Kensington Campus, London SW7 2AZ, England..
    O'Brien, H.
    Imperial Coll London, South Kensington Campus, London SW7 2AZ, England..
    Evans, V
    Imperial Coll London, South Kensington Campus, London SW7 2AZ, England..
    Angelini, V
    Imperial Coll London, South Kensington Campus, London SW7 2AZ, England..
    Kinetic electrostatic waves and their association with current structures in the solar wind2021In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 656, article id A23Article in journal (Refereed)
    Abstract [en]

    Context. A variety of kinetic electrostatic and electromagnetic waves develop in the solar wind and the relationship between these waves and larger scale structures, such as current sheets and ongoing turbulence, remain a topic of investigation. Similarly, the instabilities producing ion-acoustic waves in the solar wind are still an open question.

    Aims. The goals of this paper are to investigate electrostatic Langmuir and ion-acoustic waves in the solar wind at 0.5 AU and determine whether current sheets and associated streaming instabilities can produce the observed waves. The relationship between these waves and currents observed in the solar wind is investigated statistically.

    Methods. Solar Orbiter's Radio and Plasma Waves instrument suite provides high-resolution snapshots of the fluctuating electric field. The Low Frequency Receiver resolves the waveforms of ion-acoustic waves and the Time Domain Sampler resolves the waveforms of both ion-acoustic and Langmuir waves. Using these waveform data, we determine when these waves are observed in relation to current structures in the solar wind, estimated from the background magnetic field.

    Results. Langmuir and ion-acoustic waves are frequently observed in the solar wind. Ion-acoustic waves are observed about 1% of the time at 0.5 AU. The waves are more likely to be observed in regions of enhanced currents. However, the waves typically do not occur at current structures themselves. The observed currents in the solar wind are too small to drive instability by the relative drift between single ion and electron populations. When multi-component ion or electron distributions are present, the observed currents may be sufficient for instabilities to occur. Ion beams are the most plausible source of ion-acoustic waves in the solar wind. The spacecraft potential is confirmed to be a reliable probe of the background electron density when comparing the peak frequencies of Langmuir waves with the plasma frequency calculated from the spacecraft potential.

  • 50.
    Graham, Daniel B.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Malaspina, D. M.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA.
    Lindqvist, P-A
    KTH Royal Inst Technol, Sch Elect Engn, Space & Plasma Phys, Stockholm, Sweden.
    Gershman, D. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA;Univ Maryland, Dept Astron, College Pk, MD 20742 USA.
    Plaschke, F.
    Austrian Acad Sci, Space Res Inst, Graz, Austria.
    Enhanced Escape of Spacecraft Photoelectrons Caused by Langmuir and Upper Hybrid Waves2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 9, p. 7534-7553Article in journal (Refereed)
    Abstract [en]

    The spacecraft potential is often used to infer rapid changes in the thermal plasma density. The variations in spacecraft potential associated with large-amplitude Langmuir and upper hybrid waves are investigated with the Magnetospheric Multiscale (MMS) mission. When large-amplitude Langmuir and upper hybrid waves are observed, the spacecraft potential increases. The changes in spacecraft potential are shown to be due to enhanced photoelectron escape from the spacecraft when the wave electric fields reach large amplitude. The fluctuations in spacecraft potential follow the envelope function of the Langmuir and upper hybrid waves. Comparison with the high-resolution electron moments shows that the changes in spacecraft potential associated with the waves are not due to density perturbations. Indeed, using the spacecraft potential as a density probe leads to unphysically large density fluctuations. In addition, the changes in spacecraft potential are shown to increase as density decreases: larger spacecraft potential changes are observed in the magnetosphere, than in the magnetosheath and solar wind. These results show that external electric fields can lead to unphysical results when the spacecraft potential is used as a density probe. The results suggest that fluctuations in the spacecraft potential alone cannot be used to determine whether nonlinear processes associated with Langmuir and upper hybrid waves, such as the ponderomotive force and three-wave decay, are occurring.

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