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Vigren, Erik
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Publications (10 of 40) Show all publications
Cui, J., Cao, Y.-T., Wu, X.-S., Xu, S.-S., Yelle, R. ,., Stone, S., . . . Wei, Y. (2019). Evaluating Local Ionization Balance in the Nightside Martian Upper Atmosphere during MAVEN Deep Dip Campaigns. Astrophysical Journal Letters, 876(1), Article ID L12.
Open this publication in new window or tab >>Evaluating Local Ionization Balance in the Nightside Martian Upper Atmosphere during MAVEN Deep Dip Campaigns
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2019 (English)In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 876, no 1, article id L12Article in journal (Refereed) Published
Abstract [en]

Combining the Mars Atmosphere and Volatile Evolution (MAVEN) measurements of atmospheric neutral and ion densities, electron temperature, and energetic electron intensity, we perform the first quantitative evaluation of local ionization balance in the nightside Martian upper atmosphere, a condition with the electron impact ionization (EI) of CO2 exactly balanced by the dissociative recombination (DR) of ambient ions. The data accumulated during two MAVEN Deep Dip (DD) campaigns are included: DD6 on the deep nightside with a periapsis solar zenith angle (SZA) of 165 degrees, and DD3 close to the dawn terminator with a periapsis SZA of 110 degrees. With the electron temperatures at low altitudes corrected for an instrumental effect pertaining to the MAVEN Langmuir Probe and Waves, a statistical agreement between the EI and DR rates is suggested by the data below 140 km during DD6 and below 180 km during DD3, implying that electron precipitation is responsible for the nightside Martian ionosphere under these circumstances and extra sources are not required. In contrast, a substantial enhancement in EI over DR is observed at higher altitudes during both campaigns, which we interpret as a signature of plasma escape down the tail.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
planets and satellites: atmospheres, planets and satellites: individual (Mars)
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-383845 (URN)10.3847/2041-8213/ab1b34 (DOI)000466902900002 ()
Funder
Swedish Research Council, 621-2013-4191Swedish National Space Board, 135/13Swedish National Space Board, 166/14
Available from: 2019-05-24 Created: 2019-05-24 Last updated: 2019-05-24Bibliographically approved
Vigren, E. & Eriksson, A. I. (2019). On the ion-neutral coupling in cometary comae. Monthly notices of the Royal Astronomical Society, 482(2), 1937-1941
Open this publication in new window or tab >>On the ion-neutral coupling in cometary comae
2019 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 482, no 2, p. 1937-1941Article in journal (Refereed) Published
Abstract [en]

In a cometary coma, the ion-neutral decoupling distance, sometimes referred to as the ion exobase or collisionopause, can be defined as the cometocentric distance, r(in), where ions, initially moving with the neutral outgassing speed, have a probability of 1/e of not colliding with neutrals on their subsequent journey radially outwards. We present an analytical model for calculating this decoupling distance in the presence of a static radial electric field. We show that for a logarithmically decaying potential, the value of r(in) can even decrease to similar to 15 per cent of its field-free case value. Moreover, already at this distance, the effective ion speed can be expected to markedly exceed the neutral expansion velocity. These analytical results are in line with previous numerical calculations, adapting similar but not identical field profiles. The presence of a non-negligible ambipolar electric field and limited importance of ion-neutral collisional coupling are further supported by observations in the diamagnetic cavity of comet 67P/Churyumov-Gerasimenko by plasma instruments onboard Rosetta that reveal ion speeds several times higher than the neutral expansion velocity.

Keywords
molecular processes, comets (general)
National Category
Astronomy, Astrophysics and Cosmology Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-374113 (URN)10.1093/mnras/sty2869 (DOI)000454578700037 ()
Available from: 2019-01-23 Created: 2019-01-23 Last updated: 2019-01-23Bibliographically approved
Morooka, M., Wahlund, J.-E., Hadid, L. Z., Eriksson, A. I., Edberg, N. J. T., Vigren, E., . . . Perry, M. (2019). Saturn's Dusty Ionosphere. Journal of Geophysical Research - Space Physics, 124(3), 1679-1697
Open this publication in new window or tab >>Saturn's Dusty Ionosphere
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2019 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 3, p. 1679-1697Article in journal (Refereed) Published
Abstract [en]

Measurements of electrons and ions in Saturn's ionosphere down to 1,500-km altitudes as well as the ring crossing region above the ionosphere obtained by the Langmuir probe onboard the Cassini spacecraft are presented. Five nearly identical deep ionosphere flybys during the Grand Finale orbits and the Final plunge orbit revealed a rapid increase in the plasma densities and discrepancies between the electrons and ions densities (N-e and N-i) near the closest approach. The small N-e/N-i ratio indicates the presence of a dusty plasma, a plasma which charge carrier is dominated by negatively charged heavy particles. Comparison of the Langmuir probe obtained density with the light ion density obtained by the Ion and Neutral Mass Spectrometer confirmed the presence of heavy ions. An unexpected positive floating potential of the probe was also observed when N-e/N-i << 1. This suggests that Saturn's ionosphere near the density peak is in a dusty plasma state consisting of negatively and positively charged heavy cluster ions. The electron temperature (T-e) characteristics in the ionosphere are also investigated and unexpectedly high electron temperature value, up to 5000 K, has been observed below 2,500-km altitude in a region where electron-neutral collisions should be prominent. A well-defined relationship between T-e and N-e/N-i ratio was found, implying that the electron heating at low altitudes is related to the dusty plasma state of the ionosphere.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2019
Keywords
Saturn's ionosphere, dusty plasma, Langmuir probe, plasma density, electron temperature
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-387566 (URN)10.1029/2018JA026154 (DOI)000466087900016 ()
Funder
Swedish Research Council, 621-2013-4191Swedish Research Council, 2.2.1-312/16Swedish National Space Board, Dnr 174/15 135/13 162/14
Available from: 2019-06-24 Created: 2019-06-24 Last updated: 2019-06-24Bibliographically approved
Edberg, N. J. T., Eriksson, A., Vigren, E., Johansson, F., Goetz, C., Nilsson, H., . . . Henri, P. (2019). The Convective Electric Field Influence on the Cold Plasma and Diamagnetic Cavity of Comet 67P. Astronomical Journal, 158(2), Article ID 71.
Open this publication in new window or tab >>The Convective Electric Field Influence on the Cold Plasma and Diamagnetic Cavity of Comet 67P
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2019 (English)In: Astronomical Journal, ISSN 0004-6256, E-ISSN 1538-3881, Vol. 158, no 2, article id 71Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
comets: individual (67P), magnetic fields, plasmas, space vehicles: instruments
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-391291 (URN)10.3847/1538-3881/ab2d28 (DOI)000476604700001 ()
Funder
Swedish Research Council, 621-2013-4191Swedish Research Council, 621-2014-5526Swedish National Space Board, 109/12Swedish National Space Board, 135/13
Available from: 2019-08-22 Created: 2019-08-22 Last updated: 2019-08-22Bibliographically approved
Wu, X.-S. -., Cui, J., Xu, S. S., Lillis, R. J., Yelle, R. V., Edberg, N. J. T., . . . Mitchell, D. L. (2019). The Morphology of the Topside Martian Ionosphere: Implications on Bulk Ion Flow. Journal of Geophysical Research - Planets, 124(3), 734-751
Open this publication in new window or tab >>The Morphology of the Topside Martian Ionosphere: Implications on Bulk Ion Flow
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2019 (English)In: Journal of Geophysical Research - Planets, ISSN 2169-9097, E-ISSN 2169-9100, Vol. 124, no 3, p. 734-751Article in journal (Refereed) Published
Abstract [en]

Abstract

Prior to the Mars Atmosphere and Volatile Evolution mission, the only information on the composition of the Martian ionosphere came from the Viking Retarding Potential Analyzer data, revealing the presence of substantial ion outflow on the dayside of Mars. Extensive measurements made by the Mars Atmosphere and Volatile Evolution Neutral Gas and Ion Mass Spectrometer allow us to examine the morphology of the Martian ionosphere not only in unprecedented detail but also on both the dayside and the nightside of the planet. Above 300 km, various ionospheric species present a roughly constant density scale height around 100 km on the dayside and 180 km on the nightside. An evaluation of the ion force balance, appropriate for regions with near‐horizontal magnetic field lines, suggests the presence of supersonic ion outflow predominantly driven by the ambient magnetic pressure, with characteristic dayside and nightside flow velocities of 4 and 20 km/s, respectively, both referred to an altitude of 500 km. The corresponding total ion outflow rates are estimated to be 5 × 1025 s−1 on the dayside and 1 × 1025 s−1 on the nightside. The data also indicate a prominent variation with magnetic field orientation in that the ion distribution over regions with near‐vertical field lines tends to be more extended on the dayside but more concentrated on the nightside, as compared to regions with near‐horizontal field lines. These observations should have important implications on the pattern of ion dynamics in the vicinity of Mars.

Abstract [en]

Plain Language Summary

Prior to the Mars Atmosphere and Volatile Evolution mission, the only information on the composition of the Martian ionosphere came from the Viking Retarding Potential Analyzer data acquired on the dayside of Mars. Recently, extensive measurements made by the Mars Atmosphere and Volatile Evolution Neutral Gas and Ion Mass Spectrometer allow us to examine the Martian ionosphere not only in unprecedented detail but also on both the dayside and the nightside of the planet. By analyzing these data, we find that on each side, many of the detected ion species share a common density structure at altitudes above 300 km. Meanwhile, such a structure is clearly influenced by the ambient magnetic fields, which are well known to be inhomogeneous on Mars and cluster over the Southern Hemisphere. Near strong magnetic fields, the Martian ionosphere tends to be more extended on the dayside but more concentrated on the nightside. These findings reveal the presence of supersonic ion outflow on Mars. Such an ion outflow makes a significant contribution to plasma escape, which influences the long‐term evolution of the planet.

Keywords
Martian ionosphere, ion outflow, magnetic pressure, crustal magnetic anomalies
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-382661 (URN)10.1029/2018JE005895 (DOI)000463994500005 ()
Funder
Swedish Research Council, 621-2013-4191Swedish National Space Board, 135/13; 166/14
Available from: 2019-05-07 Created: 2019-05-07 Last updated: 2019-05-07Bibliographically approved
Vigren, E. (2018). Analytic model of comet ionosphere chemistry. Astronomy and Astrophysics, 616, Article ID A59.
Open this publication in new window or tab >>Analytic model of comet ionosphere chemistry
2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 616, article id A59Article in journal (Refereed) Published
Abstract [en]

Context. We consider a weakly to moderately active comet and make the following simplifying assumptions: (i) The partial ionization frequencies are constant throughout the considered part of the coma. (ii) All species move radially outward with the same constant speed. (iii) Ion-neutral reactions affect the chemical composition of the ions, but ion removal through dissociative recombination with free electrons is negligible. Aims. We aim to derive an analytical model for the radial variation of the abundances of various cometary ions. Methods. We present two methods for retrieving the ion composition as a function of r. The first method, which has previously been used frequently, solves a series of coupled differential equations. The new method introduced here is based on probabilistic arguments and is analytical in nature. Results. For a pure H2O coma, the resulting closed-form expressions yield results that are identical to the standard method, but are computationally much less expensive. Conclusions. In addition to the computational simplicity, the analytical model provides insight into how the various abundances depend on parameters such as comet production rate, outflow speed, and reaction rate coefficients. It can also be used to investigate limiting cases. It cannot easily be extended to account for a radially varying flow speed or dissociative recombination in the way a code based on numerical integrations can.

Keywords
comets: general, molecular processes
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-362647 (URN)10.1051/0004-6361/201832704 (DOI)000441823300001 ()
Funder
Swedish National Space Board, 166/14
Available from: 2018-10-08 Created: 2018-10-08 Last updated: 2018-10-08Bibliographically approved
Engelhardt, I. A. A., Eriksson, A. I., Vigren, E., Valliéres, X., Rubin, M., Gilet, N. & Henri, P. (2018). Cold electrons at comet 67P/Churyumov-Gerasimenko. Astronomy and Astrophysics, Article ID A51.
Open this publication in new window or tab >>Cold electrons at comet 67P/Churyumov-Gerasimenko
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2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, article id A51Article in journal (Refereed) Published
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.

National Category
Fusion, Plasma and Space Physics
Research subject
Physics with specialization in Space and Plasma Physics
Identifiers
urn:nbn:se:uu:diva-348472 (URN)10.1051/0004-6361/201833251 (DOI)000441817100004 ()
Funder
Swedish National Space Board, 171/12, 109/12, 166/14The European Space Agency (ESA)
Available from: 2018-04-18 Created: 2018-04-18 Last updated: 2018-11-12Bibliographically approved
Wahlund, J.-E., Morooka, M. W., Hadid, L. Z., Persoon, A. M., Farrell, W. M., Gurnett, D. A., . . . Vigren, E. (2018). In situ measurements of Saturn's ionosphere show that it is dynamic and interacts with the rings. Science, 359(6371), 66-68
Open this publication in new window or tab >>In situ measurements of Saturn's ionosphere show that it is dynamic and interacts with the rings
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2018 (English)In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 359, no 6371, p. 66-68Article in journal (Refereed) Published
Abstract [en]

The ionized upper layer of Saturn's atmosphere, its ionosphere, provides a closure of currents mediated by the magnetic field to other electrically charged regions (for example, rings) and hosts ion-molecule chemistry. In 2017, the Cassini spacecraft passed inside the planet's rings, allowing in situ measurements of the ionosphere. The Radio and Plasma Wave Science instrument detected a cold, dense, and dynamic ionosphere at Saturn that interacts with the rings. Plasma densities reached up to 1000 cubic centimeters, and electron temperatures were below 1160 kelvin near closest approach. The density varied between orbits by up to two orders of magnitude. Saturn's A- and B-rings cast a shadow on the planet that reduced ionization in the upper atmosphere, causing a north-south asymmetry.

National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-341494 (URN)10.1126/science.aao4134 (DOI)000419324700067 ()29229651 (PubMedID)
Available from: 2018-02-21 Created: 2018-02-21 Last updated: 2018-02-21Bibliographically approved
Odelstad, E., Eriksson, A. I., Johansson, F. L., Vigren, E., Henri, P., Gilet, N., . . . André, M. (2018). Ion Velocity and Electron Temperature Inside and Around the Diamagnetic Cavity of Comet 67P. Journal of Geophysical Research - Space Physics, 123(7), 5870-5893
Open this publication in new window or tab >>Ion Velocity and Electron Temperature Inside and Around the Diamagnetic Cavity of Comet 67P
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2018 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 7, p. 5870-5893Article in journal (Refereed) Published
Abstract [en]

Abstract A major point of interest in cometary plasma physics has been the diamagnetic cavity, an unmagnetized region in the innermost part of the coma. Here we combine Langmuir and Mutual Impedance Probe measurements to investigate ion velocities and electron temperatures in the diamagnetic cavity of comet 67P, probed by the Rosetta spacecraft. We find ion velocities generally in the range 2?4 km/s, significantly above the expected neutral velocity 1 km/s, showing that the ions are (partially) decoupled from the neutrals, indicating that ion-neutral drag was not responsible for balancing the outside magnetic pressure. Observations of clear wake effects on one of the Langmuir probes showed that the ion flow was close to radial and supersonic, at least with respect to the perpendicular temperature, inside the cavity and possibly in the surrounding region as well. We observed spacecraft potentials  V throughout the cavity, showing that a population of warm (?5 eV) electrons was present throughout the parts of the cavity reached by Rosetta. Also, a population of cold ( ) electrons was consistently observed throughout the cavity, but less consistently in the surrounding region, suggesting that while Rosetta never entered a region of collisionally coupled electrons, such a region was possibly not far away during the cavity crossings.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2018
Keywords
comets, Rosetta, plasma, diamagnetic cavity, ion velocity, electron temperature
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics with specialization in Space and Plasma Physics
Identifiers
urn:nbn:se:uu:diva-356424 (URN)10.1029/2018JA025542 (DOI)000442664300043 ()
Funder
Swedish National Space Board, 109/12, 168/15, 166/14Swedish Research Council, 621-2013-4191
Note

Article published in Early View on 25 July, 2018

Available from: 2018-07-26 Created: 2018-07-26 Last updated: 2018-11-05Bibliographically approved
Hadid, L. Z., Morooka, M. W., Wahlund, J.-E., Moore, L., Cravens, T. E., Hedman, M. M., . . . Eriksson, A. I. (2018). Ring Shadowing Effects on Saturn's Ionosphere: Implications for Ring Opacity and Plasma Transport. Geophysical Research Letters, 45(19), 10084-10092
Open this publication in new window or tab >>Ring Shadowing Effects on Saturn's Ionosphere: Implications for Ring Opacity and Plasma Transport
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2018 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 19, p. 10084-10092Article in journal (Refereed) Published
Abstract [en]

We present new results obtained by the Radio and Plasma Wave Science Langmuir probe on board Cassini during the Grand Finale. The total direct current sampled by the Langmuir probe at negative bias voltage is used to study the effect of the ring shadows on the structure of the Kronian topside ionosphere. The D and C rings and the Cassini Division are confirmed to be optically thin to extreme ultraviolet solar radiation. However, different responses from the opaque A and B rings are observed. The edges of the A ring shadow are shown to match the A ring boundaries, unlike the B ring, which indicates variable responses to the B ring shadow. We show that the variable responses are due to the ionospheric plasma, more precisely to the longer chemical lifetime of H+ compared to H-2(+) and H-3(+), suggesting that the plasma is transported from the sunlit region to the shadowed one in the ionosphere. Plain Language Summary As Saturn's northern hemisphere experienced summer during the Grand Finale, the planet's northern dayside hemisphere and its rings were fully illuminated by the Sun. However, the southern hemisphere was partly obscured because of the shadows cast by the A and B rings. Using the in situ measurements of the Langmuir probe part of the Radio and Plasma Wave Science investigation on board the Cassini spacecraft, we study for the first time the effect of the ring shadows on Saturn's ionosphere. From the ring shadows signatures on the total ion current collected by the Langmuir probe, we show that the A and B rings are optically thicker (to the solar extreme ultraviolet radiation) than the inner C and D rings and the Cassini Division to the solar extreme ultraviolet radiation. Moreover, we reproduce the boundaries of the A ring and the outer edge of the B ring. Furthermore, observed variations with respect to the inner edge of the B ring imply a delayed response of the ionospheric H+ because of its long lifetime and suggest that the ionospheric plasma is transported from an unshadowed region to a shadowed one in the ionosphere.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2018
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-387257 (URN)10.1029/2018GL079150 (DOI)000448656800007 ()
Funder
Swedish Research Council, 2016-05364Swedish Research Council, 621-2013-4191
Available from: 2019-06-26 Created: 2019-06-26 Last updated: 2019-06-26Bibliographically approved
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