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Vigren, Erik
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Publications (10 of 44) Show all publications
Vigren, E. & Cui, J. (2019). Electron Temperatures in the Dayside Ionosphere of Mars Derived from O-2(+) Chemistry. Astrophysical Journal, 887(2), Article ID 177.
Open this publication in new window or tab >>Electron Temperatures in the Dayside Ionosphere of Mars Derived from O-2(+) Chemistry
2019 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 887, no 2, article id 177Article in journal (Refereed) Published
Abstract [en]

From a reduced chemical model of the Martian dayside ionosphere we derive an expression that can be used to estimate the electron temperature as a function of the ambient number densities of CO2, O, O-2(+), CO2+, O+, and NO+ and the total ion number density. The model is tested in the sunlit ionosphere with Mars Atmosphere and Volatile EvolutioN/Neutral Gas Ion Mass Spectrometer (MAVEN/NGIMS) data from the Deep Dip campaigns DD2 (2015 April) and DD8 (2017 October). Around an altitude of similar to 130-140 km the calculated electron temperatures along the DD2 orbits are in many cases compatible with the neutral temperatures derived from the CO2 density profiles and downward integration of the hydrostatic balance equation, indicating efficient cooling of the electron population. For altitudes below 170 km the electron temperature (constructed from median density profiles) are higher for DD8 than for DD2 which we link to atmospheric solar cycle modulation. Median electron temperatures derived for DD2 and DD8 are roughly similar when inspecting similar CO2 number densities and a simple power law is proposed to relate the electron temperature to the CO2 number density. Calculated electron temperatures of approximately 1000.K around an altitude of 180-200 km appear not to conflict with published data from MAVEN Langmuir Probe Wave (LPW) measurements. At greater depths the LPW-derived electron temperatures have been reported as biased high and so a detailed comparison with results from the present work is merely proposed as a dedicated follow-up study.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-405351 (URN)10.3847/1538-4357/ab53db (DOI)000506012000071 ()
Funder
Swedish National Space Board, Dnr 166/14
Available from: 2020-02-28 Created: 2020-02-28 Last updated: 2020-02-28Bibliographically approved
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
Mandt, K. E., Eriksson, A., Beth, A., Galand, M. & Vigren, E. (2019). Influence of collisions on ion dynamics in the inner comae of four comets. Astronomy and Astrophysics, 630, Article ID A48.
Open this publication in new window or tab >>Influence of collisions on ion dynamics in the inner comae of four comets
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2019 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 630, article id A48Article in journal (Refereed) Published
Abstract [en]

Context: Collisions between cometary neutrals in the inner coma of a comet and cometary ions that have been picked up into the solar wind flow and return to the coma lead to the formation of a broad inner boundary known as a collisionopause. This boundary is produced by a combination of charge transfer and chemical reactions, both of which are important at the location of the collisionopause boundary. Four spacecraft measured ion densities and velocities in the inner region of comets, exploring the part of the coma where an ion-neutral collisionopause boundary is expected to form.

Aims: The aims are to determine the dominant physics behind the formation of the ion-neutral collisionopause and to evaluate where this boundary has been observed by spacecraft.

Methods: We evaluated observations from three spacecraft at four different comets to determine if a collisionopause boundary was observed based on the reported ion velocities. We compared the measured location of the ion-neutral collisionopause with measurements of the collision cross sections to evaluate whether chemistry or charge exchange are more important at the location where the collisionopause is observed.

Results: Based on measurements of the cross sections for charge transfer and for chemical reactions, the boundary observed by Rosetta appears to be the location where chemistry becomes the more probable result of a collision between H2O and H2O+ than charge exchange. Comparisons with ion observations made by Deep Space 1 at 19P/Borrelly and Giotto at 1P/Halley and 26P/Grigg-Skjellerup show that similar boundaries were observed at 19P/Borrelly and 1P/Halley. The ion composition measurements made by Giotto at Halley confirm that chemistry becomes more important inside of this boundary and that electron-ion dissociative recombination is a driver for the reported ion pileup boundary.

Place, publisher, year, edition, pages
EDP SCIENCES S A, 2019
Keywords
molecular processes, plasmas, comets: individual: 67P/Churyumov-Gerasimenko, comets: individual: 1P/Halley, comets: individual: 19P/Borelly, comets: individual: 26P/Grigg-Skjellerup
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-395683 (URN)10.1051/0004-6361/201834828 (DOI)000486989400047 ()
Available from: 2019-10-24 Created: 2019-10-24 Last updated: 2019-10-24Bibliographically 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
Hadid, L. Z., Morooka, M. W., Wahlund, J.-E., Persoon, A. M., Andrews, D. J., Shebanits, O., . . . Eriksson, A. I. (2019). Saturn's Ionosphere: Electron Density Altitude Profiles and D-Ring Interaction From The Cassini Grand Finale. Geophysical Research Letters, 46(16), 9362-9369
Open this publication in new window or tab >>Saturn's Ionosphere: Electron Density Altitude Profiles and D-Ring Interaction From The Cassini Grand Finale
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2019 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 16, p. 9362-9369Article in journal (Refereed) Published
Abstract [en]

We present the electron density (n(e)) altitude profiles of Saturn's ionosphere at near-equatorial latitudes from all 23 orbits of Cassini's Grand Finale. The data are collected by the Langmuir probe part of the Radio and Plasma Wave Science investigation. A high degree of variability in the electron density profiles is observed. However, organizing them by consecutive altitude ranges revealed clear differences between the southern and northern hemispheres. The n(e) profiles are shown to be more variable and connected to the D-ring below 5,000 km in the southern hemisphere compared to the northern hemisphere. This observed variability is explained to be a consequence of an electrodynamic interaction with the D-ring. Moreover, a density altitude profile is constructed for the northern hemisphere indicating the presence of three different ionospheric layers. Similar properties were observed during Cassini's final plunge, where the main ionospheric peak is crossed at similar to 1,550-km altitude. Plain Language Summary The Cassini Langmuir probe measured directly the uppermost layer of Saturn's atmosphere, the ionosphere, during its Grand Finale. The observations revealed a layered electron density altitude profile with evidence in the southern hemisphere of an electrodynamic type of interaction with the planet innermost D-ring. Moreover, the main peak of the ionosphere is observed for the first time in the final plunge around 1,550 km.

National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-396547 (URN)10.1029/2018GL078004 (DOI)000490966700007 ()
Funder
Swedish National Space BoardSwedish Research Council, 2016-05364Swedish National Space Board, Dnr 174/15Swedish National Space Board, Dnr 135/13Swedish Research Council, 621-2013-4191
Available from: 2019-11-07 Created: 2019-11-07 Last updated: 2019-11-07Bibliographically 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
Vigren, E., Edberg, N. J. T., Eriksson, A., Galand, M., Henri, P., Johansson, F., . . . Vallieres, X. (2019). The Evolution of the Electron Number Density in the Coma of Comet 67P at the Location of Rosetta from 2015 November through 2016 March. Astrophysical Journal, 881(1), Article ID 6.
Open this publication in new window or tab >>The Evolution of the Electron Number Density in the Coma of Comet 67P at the Location of Rosetta from 2015 November through 2016 March
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2019 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 881, no 1, article id 6Article in journal (Refereed) Published
Abstract [en]

A comet ionospheric model assuming the plasma moves radially outward with the same bulk speed as the neutral gas and not being subject to severe reduction through dissociative recombination has previously been tested in a series of case studies associated with the Rosetta mission at comet 67P/Churyumov-Gerasimenko. It has been found that at low activity and within several tens of kilometers from the nucleus such models (which originally were developed for such conditions) generally work well in reproducing observed electron number densities, in particular when plasma production through both photoionization and electron-impact ionization is taken into account. Near perihelion, case studies have, on the contrary, shown that applying similar assumptions overestimates the observed electron number densities at the location of Rosetta. Here we compare Rosetta Orbiter Spectrometer for Ion and Neutral Analysis/Comet Pressure sensor-driven model results with Rosetta Plasma Consortium/Mutual Impedance Probe-derived electron number densities for an extended time period (2015 November through 2016 March) during the postperihelion phase with southern summer/spring. We observe a gradual transition from a state when the model grossly overestimates (by more than a factor of 10) the observations to being in reasonable agreement during 2016 March.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
comets: individual (67P), molecular processes
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-393332 (URN)10.3847/1538-4357/ab29f7 (DOI)000479099500006 ()
Funder
Swedish Research Council, 621-2013-4191Swedish Research Council, 621-2014-5526Swedish National Space Board, 109/02Swedish National Space Board, 114/13Swedish National Space Board, 135/13Swedish National Space Board, 166/14
Available from: 2019-09-27 Created: 2019-09-27 Last updated: 2019-09-27Bibliographically 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
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