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Eriksson, A. I., Engelhardt, I. A. A., André, M., Boström, R., Edberg, N. J. T., Johansson, F. L., . . . Norberg, C. (2017). Cold and warm electrons at comet 67P/Churyumov-Gerasimenko. Astronomy and Astrophysics, 605, Article ID A15.
Open this publication in new window or tab >>Cold and warm electrons at comet 67P/Churyumov-Gerasimenko
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2017 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 605, article id A15Article in journal (Refereed) Published
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.

Keywords
comets: general, plasmas, space vehicles: instruments
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-337755 (URN)10.1051/0004-6361/201630159 (DOI)000412231200111 ()
Funder
Swedish National Space Board, 109/12; 171/12; 135/13; 166/14; 168/15Swedish Research Council, 621-2013-4191
Note

Funding: The results presented here are only possible thanks to the combined efforts over 20 yr by many groups and individuals involved in Rosetta, including but not restricted to the ESA project teams at ESTEC, ESOC and ESAC and all people involved in designing, building, testing and operating RPC and LAP. We thank Kathrin Altwegg for discussions of the pulses in LAP and COPS. Rosetta is a European Space Agency (ESA) mission with contributions from its member states and the National Aeronautics and Space Administration (NASA). The work on RPC-LAP data was funded by the Swedish National Space Board under contracts 109/12, 171/12, 135/13, 166/14 and 168/15, and by Vetenskapsradet under contract 621-2013-4191. This work has made use of the AMDA and RPC Quicklook database, provided by a collaboration between the Centre de Donnees de la Physique des Plasmas CDPP (supported by CNRS, CNES, Observatoire de Paris and Universite Paul Sabatier, Toulouse), and Imperial College London (supported by the UK Science and Technology Facilities Council).

Available from: 2018-01-12 Created: 2018-01-12 Last updated: 2018-04-18Bibliographically approved
Li, K., Wei, Y., André, M., Eriksson, A., Haaland, S., Kronberg, E. A., . . . Wan, W. X. (2017). Cold Ion Outflow Modulated by the Solar Wind Energy Input and Tilt of the Geomagnetic Dipole. Journal of Geophysical Research - Space Physics, 122(10), 10658-10668
Open this publication in new window or tab >>Cold Ion Outflow Modulated by the Solar Wind Energy Input and Tilt of the Geomagnetic Dipole
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2017 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 10, p. 10658-10668Article in journal (Refereed) Published
Abstract [en]

The solar wind energy input into the Earth's magnetosphere-ionosphere system drives ionospheric outflow, which plays an important role in both the magnetospheric dynamics and evolution of the atmosphere. However, little is known about the cold ion outflow with energies lower than a few tens of eV, as the direct measurement of cold ions is difficult because a spacecraft gains a positive electric charge due to the photoemission effect, which prevents cold ions from reaching the onboard detectors. A recent breakthrough in the measurement technique using Cluster spacecraft revealed that cold ions dominate the ion population in the magnetosphere. This new technique yields a comprehensive data set containing measurements of the velocities and densities of cold ions for the years 2001-2010. In this paper, this data set is used to analyze the cold ion outflow from the ionosphere. We found that about 0.1% of the solar wind energy input is transformed to the kinetic energy of cold ion outflow at the topside ionosphere. We also found that the geomagnetic dipole tilt can significantly affect the density of cold ion outflow, modulating the outflow rate of cold ion kinetic energy. These results give us clues to study the evolution of ionospheric outflow with changing global magnetic field and solar wind condition in the history.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2017
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-342097 (URN)10.1002/2017JA024642 (DOI)000419937800063 ()
Available from: 2018-02-19 Created: 2018-02-19 Last updated: 2018-02-19Bibliographically approved
Li, W. Y., André, M., Khotyaintsev, Y. V., Vaivads, A., Fuselier, S. A., Graham, D. B., . . . Burch, J. (2017). Cold Ionospheric Ions in the Magnetic Reconnection Outflow Region. Journal of Geophysical Research - Space Physics, 122(10), 10194-10202
Open this publication in new window or tab >>Cold Ionospheric Ions in the Magnetic Reconnection Outflow Region
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2017 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 10, p. 10194-10202Article in journal (Refereed) Published
Abstract [en]

Magnetosheath plasma usually determines properties of asymmetric magnetic reconnection at the subsolar region of Earth's magnetopause. However, cold plasma that originated from the ionosphere can also reach the magnetopause and modify the kinetic physics of asymmetric reconnection. We present a magnetopause crossing with high-density (10-60 cm(-3)) cold ions and ongoing reconnection from the observation of the Magnetospheric Multiscale (MMS) spacecraft. The magnetopause crossing is estimated to be 300 ion inertial lengths south of the X line. Two distinct ion populations are observed on the magnetosheath edge of the ion jet. One population with high parallel velocities (200-300 km/s) is identified to be cold ion beams, and the other population is the magnetosheath ions. In the deHoffman-Teller frame, the field-aligned magnetosheath ions are Alfvenic and move toward the jet region, while the field-aligned cold ion beams move toward the magnetosheath boundary layer, with much lower speeds. These cold ion beams are suggested to be from the cold ions entering the jet close to the X line. This is the first observation of the cold ionospheric ions in the reconnection outflow region, including the reconnection jet and the magnetosheath boundary layer.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2017
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-342096 (URN)10.1002/2017JA024287 (DOI)000419937800031 ()
Available from: 2018-03-02 Created: 2018-03-02 Last updated: 2018-03-02Bibliographically approved
Toledo-Redondo, S., André, M., Khotyaintsev, Y. V., Lavraud, B., Vaivads, A., Graham, D. B., . . . Burch, J. L. (2017). Energy budget and mechanisms of cold ion heating in asymmetric magnetic reconnection. Journal of Geophysical Research - Space Physics, 122(9), 9396-9413
Open this publication in new window or tab >>Energy budget and mechanisms of cold ion heating in asymmetric magnetic reconnection
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2017 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 9, p. 9396-9413Article in journal (Refereed) Published
Abstract [en]

Cold ions (few tens of eV) of ionospheric origin are commonly observed on the magnetospheric side of the Earth's dayside magnetopause. As a result, they can participate in magnetic reconnection, changing locally the reconnection rate and being accelerated and heated. We present four events where cold ion heating was observed by the Magnetospheric Multiscale mission, associated with the magnetospheric Hall E field region of magnetic reconnection. For two of the events the cold ion density was small compared to the magnetosheath density, and the cold ions were heated roughly to the same temperature as magnetosheath ions inside the exhaust. On the other hand, for the other two events the cold ion density was comparable to the magnetosheath density and the cold ion heating observed was significantly smaller. Magnetic reconnection converts magnetic energy into particle energy, and ion heating is known to dominate the energy partition. We find that at least 10-25% of the energy spent by reconnection into ion heating went into magnetospheric cold ion heating. The total energy budget for cold ions may be even higher when properly accounting for the heavier species, namely helium and oxygen. Large E field fluctuations are observed in this cold ion heating region, i.e., gradients and waves, that are likely the source of particle energization.

Plain Language Summary: The magnetic field of Earth creates a natural shield that isolates and protects us from the particles and fields coming from our star, the Sun. This natural shield is called the magnetosphere and is filled by plasma. The particles coming from the Sun form another plasma called the solar wind and are usually deviated around the magnetosphere. However, under certain circumstances these two plasmas can reconnect (magnetic reconnection), and part of the energy and mass of the two plasmas is interchanged. Magnetic reconnection is the driver of storms and substorms inside the magnetosphere. In this work, we investigate what occurs to particles of very low energy (cold ions) of ionospheric origin when they reach the reconnecting boundary of the magnetosphere. It is found that they are energized and take an important part of the energy spent in reconnecting the plasmas. The plasma boundary develops spatial structures and emits waves that are able to heat the cold ions. Once heated, these cold ions irreversibly will escape the Earth's magnetosphere to never come back to Earth.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-340160 (URN)10.1002/2017JA024553 (DOI)000413491700021 ()
Available from: 2018-02-01 Created: 2018-02-01 Last updated: 2018-02-01Bibliographically approved
Khotyaintsev, Y. V., Divin, A., Vaivads, A., André, M. & Markidis, S. (2017). Energy conversion at dipolarization fronts. Geophysical Research Letters, 44(3), 1234-1242
Open this publication in new window or tab >>Energy conversion at dipolarization fronts
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2017 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, no 3, p. 1234-1242Article in journal (Refereed) Published
Abstract [en]

We use multispacecraft observations by Cluster in the Earth's magnetotail and 3-D particle-in-cell simulations to investigate conversion of electromagnetic energy at the front of a fast plasma jet. We find that the major energy conversion is happening in the Earth (laboratory) frame, where the electromagnetic energy is being transferred from the electromagnetic field to particles. This process operates in a region with size of the order several ion inertial lengths across the jet front, and the primary contribution to E . j is coming from the motional electric field and the ion current. In the frame of the front we find fluctuating energy conversion with localized loads and generators at sub-ion scales which are primarily related to the lower hybrid drift instability excited at the front; however, these provide relatively small net energy conversion.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2017
National Category
Astronomy, Astrophysics and Cosmology Geophysics
Identifiers
urn:nbn:se:uu:diva-319094 (URN)10.1002/2016GL071909 (DOI)000396115000006 ()
Funder
Swedish National Space Board, 136/11Swedish National Infrastructure for Computing (SNIC), 2014-8-38 SNIC 2016/1-457
Available from: 2017-04-03 Created: 2017-04-03 Last updated: 2017-11-29Bibliographically approved
Fu, H. S., Vaivads, A., Khotyaintsev, Y. V., André, M., Cao, J. B., Olshevsky, V., . . . Retino, A. (2017). Intermittent energy dissipation by turbulent reconnection. Geophysical Research Letters, 44(1), 37-43
Open this publication in new window or tab >>Intermittent energy dissipation by turbulent reconnection
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2017 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, no 1, p. 37-43Article in journal (Refereed) Published
Abstract [en]

Magnetic reconnectionthe process responsible for many explosive phenomena in both nature and laboratoryis efficient at dissipating magnetic energy into particle energy. To date, exactly how this dissipation happens remains unclear, owing to the scarcity of multipoint measurements of the diffusion region at the sub-ion scale. Here we report such a measurement by Clusterfour spacecraft with separation of 1/5 ion scale. We discover numerous current filaments and magnetic nulls inside the diffusion region of magnetic reconnection, with the strongest currents appearing at spiral nulls (O-lines) and the separatrices. Inside each current filament, kinetic-scale turbulence is significantly increased and the energy dissipation, Ej, is 100 times larger than the typical value. At the jet reversal point, where radial nulls (X-lines) are detected, the current, turbulence, and energy dissipations are surprisingly small. All these features clearly demonstrate that energy dissipation in magnetic reconnection occurs at O-lines but not X-lines.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2017
Keywords
turbulent reconnection, energy dissipation, turbulence, magnetic nulls, current filaments, intermittence
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-318611 (URN)10.1002/2016GL071787 (DOI)000393954900005 ()
Funder
Swedish Research Council
Available from: 2017-03-27 Created: 2017-03-27 Last updated: 2017-11-29Bibliographically approved
Graham, D. B., Khotyaintsev, Y. V., Norgren, C., Vaivads, A., André, M., Toledo-Redondo, S., . . . Burch, J. L. (2017). Lower hybrid waves in the ion diffusion and magnetospheric inflow regions. Journal of Geophysical Research - Space Physics, 122(1), 517-533
Open this publication in new window or tab >>Lower hybrid waves in the ion diffusion and magnetospheric inflow regions
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2017 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 1, p. 517-533Article in journal (Refereed) Published
Abstract [en]

The role and properties of lower hybrid waves in the ion diffusion region and magnetospheric inflow region of asymmetric reconnection are investigated using the Magnetospheric Multiscale (MMS) mission. Two distinct groups of lower hybrid waves are observed in the ion diffusion region and magnetospheric inflow region, which have distinct properties and propagate in opposite directions along the magnetopause. One group develops near the ion edge in the magnetospheric inflow, where magnetosheath ions enter the magnetosphere through the finite gyroradius effect and are driven by the ion-ion cross-field instability due to the interaction between the magnetosheath ions and cold magnetospheric ions. This leads to heating of the cold magnetospheric ions. The second group develops at the sharpest density gradient, where the Hall electric field is observed and is driven by the lower hybrid drift instability. These drift waves produce cross-field particle diffusion, enabling magnetosheath electrons to enter the magnetospheric inflow region thereby broadening the density gradient in the ion diffusion region.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2017
Keywords
Magnetic reconnection, Ion diffusion region, Lower hybrid waves
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-319788 (URN)10.1002/2016JA023572 (DOI)000395655800038 ()
Funder
Swedish National Space Board
Available from: 2017-04-12 Created: 2017-04-12 Last updated: 2017-11-29Bibliographically approved
Duan, S., Dai, L., Wang, C., He, Z., Cai, C., Zhang, Y. C., . . . Khotyaintsev, Y. V. (2017). Oxygen Ions O+ Energized by Kinetic Alfven Eigenmode During Dipolarizations of Intense Substorms. Journal of Geophysical Research - Space Physics, 122(11), 11256-11273
Open this publication in new window or tab >>Oxygen Ions O+ Energized by Kinetic Alfven Eigenmode During Dipolarizations of Intense Substorms
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2017 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 11, p. 11256-11273Article in journal (Refereed) Published
Abstract [en]

Singly charged oxygen ions, O+, energized by kinetic Alfven wave eigenmode (KAWE) in the plasma sheet boundary layer during dipolarizations of two intense substorms, 10: 07 UT on 31 August 2004 and 18: 24 UT on 14 September 2004, are investigated by Cluster spacecraft in the magnetotail. It is found that after the beginning of the expansion phase of substorms, O+ ions are clearly energized in the direction perpendicular to the magnetic field with energy larger than 1 keV in the near-Earth plasma sheet during magnetic dipolarizations. The pitch angle distribution of these energetic O+ ions is significantly different from that of O+ ions with energy less than 1 keV before substorm onset that is in the quasi-parallel direction along the magnetic field. The KAWE with the large perpendicular unipolar electric field, E-z similar to -20 mV/m, significantly accelerates O+ ions in the direction perpendicular to the background magnetic field. We present good evidences that O+ ion origin from the ionosphere along the magnetic field line in the northward lobe can be accelerated in the perpendicular direction during substorm dipolarizations. The change of the move direction of O+ ions is useful for O+ transferring from the lobe into the central plasma sheet in the magnetotail. Thus, KAWE can play an important role in O+ ion transfer process from the lobe into the plasma sheet during intense substorms.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2017
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-342089 (URN)10.1002/2017JA024418 (DOI)000419938600022 ()
Available from: 2018-03-01 Created: 2018-03-01 Last updated: 2018-03-01Bibliographically approved
Peng, F. Z., Fu, H. S., Cao, J. B., Graham, D. B., Chen, Z. Z., Cao, D., . . . Burch, J. L. (2017). Quadrupolar pattern of the asymmetric guide-field reconnection. Journal of Geophysical Research - Space Physics, 122(6), 6349-6356
Open this publication in new window or tab >>Quadrupolar pattern of the asymmetric guide-field reconnection
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2017 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 6, p. 6349-6356Article in journal (Refereed) Published
Abstract [en]

With high-resolution data of the recently launched Magnetospheric Multiscale mission, we report a magnetic reconnection event at the dayside magnetopause. This reconnection event, having a density asymmetry N-high/N-low approximate to 2 on the two sides of the reconnecting current sheet and a guide field B-g approximate to 0.4B(0) in the out-of-plane direction, exhibit all the two-fluid features: Alfvenic plasma jets in the outflow region, bipolar Hall electric fields toward the current sheet center, quadrupolar Hall magnetic fields in the out-of-plane direction, and the corresponding Hall currents. Obviously, the density asymmetry N-high/N-low approximate to 2 and the guide field B-g approximate to 0.4B(0) are not sufficient to dismiss the quadrupolar pattern of Hall reconnection. This is different from previous simulations, where the bipolar pattern of Hall reconnection was suggested.

Keywords
reconnection at magnetopause, number density asymmetry, moderate guide field, Alfvenic plasma jet, quadrupolar Hall pattern
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-331893 (URN)10.1002/2016JA023666 (DOI)000405534800030 ()
Available from: 2017-10-24 Created: 2017-10-24 Last updated: 2017-10-24Bibliographically approved
Karlsson, T., Eriksson, A. I., Odelstad, E., André, M., Dickeli, G., Kullen, A., . . . Richter, I. (2017). Rosetta measurements of lower hybrid frequency range electric field oscillations in the plasma environment of comet 67P. Geophysical Research Letters, 44(4), 1641-1651
Open this publication in new window or tab >>Rosetta measurements of lower hybrid frequency range electric field oscillations in the plasma environment of comet 67P
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2017 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, no 4, p. 1641-1651Article in journal (Refereed) Published
Abstract [en]

Electric field measurements from cometary environments are very rare but can provide important information on how plasma waves help fashion the plasma environment. The long dwelling time of the Rosetta spacecraft close to comet 67P/Churyumov-Gerasimenko promises to improve this state. We here present the first electric field measurements from 67P, performed by the Rosetta dual Langmuir probe instrument LAP. Measurements of the electric field from cometocentric distances of 149 and 348 km are presented together with estimates of plasma density changes. Persistent wave activity around the local H2O+ lower hybrid frequency is observed, with the largest amplitudes observed at sharp plasma gradients. We demonstrate that the necessary requirements for the lower hybrid drift instability to be operating are fulfilled. We suggest that lower hybrid waves are responsible for the creation of a warm electron population, the origins of which have been unknown so far, by heating ambient electrons in the magnetic field-parallel direction.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-318947 (URN)10.1002/2016GL072419 (DOI)000396411100004 ()
Funder
Swedish National Space Board, 277/12
Available from: 2017-04-03 Created: 2017-04-03 Last updated: 2017-11-29Bibliographically approved
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