The ionospheres and (induced) magnetospheres of unmagnetized and weakly magnetized bodies with substantial atmospheres (e.g. Mars, Venus, Titan, Pluto and comets) are subject to disturbances due to solar activity, interplanetary conditions (e.g. solar flares, coronal mass ejections and solar energetic particles) or for moons parent magnetospheric activity. They interact similarly as their magnetized counterparts but with scientifically important differences.
As an integral part of planetary atmospheres, ionospheres are tightly coupled with the neutral atmosphere, exosphere and surrounding plasma environment, possessing rich compositional, density, and temperature structures. The interaction among neutral and charged components affects atmospheric loss, neutral winds, photochemistry, and energy balance within ionospheres.
This session invites abstracts concerning remote and in-situ data analysis, modelling studies, comparative studies, instrumentation and mission concepts for unmagnetized and weakly magnetized solar system bodies.

Co-organized by ST4
Convener: Martin Volwerk | Co-conveners: Xiaohua Fang, Christopher Fowler, Charlotte Götz
| Attendance Tue, 05 May, 14:00–15:45 (CEST)

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Chat time: Tuesday, 5 May 2020, 14:00–15:45

Chairperson: Martin Volwerk
D2863 |
Lican Shan, Aimin Du, Bruce Tsurutani, Yasong Ge, Quanming Lu, Christian Mazelle, Can Huang, Karl-Heinz Glassmeier, and Pierre Henri

Collisionless plasma shocks (CPSs), forming when supersonic plasma streams encounter a magnetized obstacle, are invoked to explain the acceleration of ubiquitously energetic cosmic rays. It has long been theorized from magnetohydrodynamics, but not directly observed that the CPSs develop from the growth of small-amplitude, low-frequency plasma waves which excited by reflected ion beams from the obstacle. We present in situ observations of an entire formation sequence of the periodic plasma shocks by the MAVEN spacecraft’s magnetic field and particle instruments. The magnetometer first detected small-amplitude circularly polarized magnetosonic waves that further steepened and eventually evolved into periodic shocks. Moreover, differing from the traditional understanding, characterizations of the fast mode waves show that the free energy of the wave/shock generation is provided by newborn protons, and the increasing sunward proton fluxes provided persistent energy for wave steepening. The unusual evidence presents itself from the combination of two circumstances: radial-aligned (Sun-Mars) magnetic fields and Martian atmospheric atom (hydrogen) photoionization and solar wind pickup. These observations lead to the conclusion that newborn ions play a crucial role in the formation process of some CPSs in the astrophysical and space plasma.

How to cite: Shan, L., Du, A., Tsurutani, B., Ge, Y., Lu, Q., Mazelle, C., Huang, C., Glassmeier, K.-H., and Henri, P.: Observations of the Formation of Periodic Plasma Shocks from Fast Mode Waves, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1508, https://doi.org/10.5194/egusphere-egu2020-1508, 2020.

D2864 |
Sofia Bergman, Gabriella Stenberg Wieser, Martin Wieser, Fredrik Johansson, and Anders Eriksson

Low-energy ions play important roles in many processes in the environments around various bodies in the solar system. At comets, they are, for example, important for the understanding of the interaction of the cometary particles with the solar wind, including the formation of the diamagnetic cavity.

Unfortunately, spacecraft charging makes low-energy ions difficult to measure using in-situ techniques. The charged spacecraft surface will attract or repel the ions prior to detection, affecting both their trajectories and energy. The affected trajectories will change the effective FOV of the instrument. A negatively charged spacecraft will focus incoming positive ions, enlarging and distorting the FOV.

We model the low-energy FOV distortion of the Ion Composition Analyzer (ICA) on board Rosetta. ICA is an ion spectrometer measuring positive ions with an energy range of a few eV to 40 keV. Rosetta was commonly charged to a negative potential throughout the mission, and consequently the positive ions were accelerated towards the spacecraft before detection. This distorted the low-energy part of the data. We use the Spacecraft Plasma Interaction Software (SPIS) to simulate the environment around the spacecraft and backtrace particles from the instrument. We then compare the travel direction of the ions at detection and infinity, and draw conclusions about the resulting FOV distortion. We investigate the distortion for different spacecraft potentials and Debye lengths of the surrounding plasma.

The results show that the effective FOV of ICA is severely distorted at low energies, but the distortion varies between different viewing directions of the instrument. It is furthermore sensitive to changes in the Debye length and we observe a small non-linearity in the relation between FOV distortion, ion energy and spacecraft potential. Generally, the FOV is not significantly affected when the energy of the ions is above twice the spacecraft potential.

How to cite: Bergman, S., Stenberg Wieser, G., Wieser, M., Johansson, F., and Eriksson, A.: The Spacecraft Potential’s Influence on the FOV of Rosetta-ICA at Low Ion Energies, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6871, https://doi.org/10.5194/egusphere-egu2020-6871, 2020.

D2865 |
Gabriella Stenberg Wieser, Martin Wieser, Sofia Bergman, Elias Odelstad, Fredrik Johansson, and Hans Nilsson

We investigate the variations in low energy cometary ions around comet 67P. Detailed measurements of these ions were made possible by implementing a new instrumental mode of the ion mass spectrometer on the Rosetta spacecraft. The nominal time resolution was increased from 192 s to 4 s at the expense of the energy range and the field-of-view.

In this study we focus on ion observations made outside of, but in the vicinity of, the diamagnetic cavity. The ion dynamics here is clearly linked to variations of the magnetic field strength and properties of the electron velocity distribution, manifested by the spacecraft potential. Preliminary results show that the ion flux correlates with the changes of the spacecraft potential. The maximum ion flux is, however, observed about 20 seconds after a sudden decrease of the potential (corresponding to an increase in electron density if electron temperature is constant). We also find evidence of small ion temperature increases both when the spacecraft potential changes fast and at the time of maximum ion flux.

How to cite: Stenberg Wieser, G., Wieser, M., Bergman, S., Odelstad, E., Johansson, F., and Nilsson, H.: Observations of low energy ions around the diamagnetic cavity at comet 67P, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8318, https://doi.org/10.5194/egusphere-egu2020-8318, 2020.

D2866 |
Christian Mazelle, Karim Meziane, Norberto Romanelli, David L. Mitchell, Suranga Ruhunisiri, Hadi Madanian, Ali Rahmati, Steven J. Schwartz, Jared R. Espley, Jasper S. Halekas, and Emmanuel Penou

Using MAVEN observations, we report variations of the amplitude of electromagnetic waves observed at the local proton cyclotron frequency upstream from the bow shock on short (plasma) time/length-scales: 1) a sharp sudden increase of the amplitude when crossing the electron foreshock boundary and 2) a decrease of this amplitude clearly correlated with the increasing distance from the shock along the magnetic field inside the foreshock without any simple relation to the planetary radial distance. These waves are excited by unstable ring-beam velocity distributions of newborn protons produced by ionization of exospheric hydrogen atoms. The amplitude of these waves is generally expected to depend only on different drivers including the observed large seasonality of the hydrogen exosphere, the EUV solar flux, the solar wind density and velocity or the IMF cone angle at different levels of importance. No noticeable wave amplitude change is expected when crossing the electron foreshock boundary and inside the pure electron foreshock. Surprisingly, we found that that these waves also display the two same aforementioned properties as the foreshock electrons fluxes at Mars though the wave origin is related to the ions only. We investigate the possibility that the extra free energy necessary to increase the wave amplitude could be due to supplementary ionization of hydrogen atoms by electron impact ionization inside the foreshock. Therefore, the electron foreshock also plays a role in the production of pickup protons which contribute to the planetary escape from high altitude.

How to cite: Mazelle, C., Meziane, K., Romanelli, N., Mitchell, D. L., Ruhunisiri, S., Madanian, H., Rahmati, A., Schwartz, S. J., Espley, J. R., Halekas, J. S., and Penou, E.: Influence of foreshock electrons impact ionization on the amplitude of pickup protons generated waves at Mars, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10596, https://doi.org/10.5194/egusphere-egu2020-10596, 2020.

D2867 |
Gangkai Poh, Jared Espley, Norberto Romanelli, Jacob Gruesbeck, and Gina DiBraccio

In this study, we present a preliminary analysis of large-amplitude sawtooth-like magnetic field oscillations observed by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft at Mars. Initial survey of these quasi-periodic magnetic field oscillations (with periods of ~3 – 4 minutes) shows distinct sawtooth-like magnetic field signatures with steep increase in BY of ~20 – 30 nT, followed by a gentle, but turbulent, return to background magnetic field values. The extrema in the BY component generally coincide with an extrema of opposite polarity in the BX component. Quasi-periodic magnetic field signatures can also be observed in the z-component of the magnetic field vector. Ion and electrons measurements shows corresponding increase in ions and electrons with energies greater than 30eV and 10 eV, respectively, during observations of these sawtooth-like oscillations, indicating some mixing of plasma. We interpret these observations as Kelvin-Helmholtz (KH) waves in the non-linear stages because the plasma and fields signatures are consistent with non-linear KH waves observed at Earth and other planetary environments. KH waves are developed as a result of flow shear-driven KH instability occurring between the boundary separating two moving fluids. In the non-linear stage of the KH instability, rolled-up KH vortex can developed along the boundary, allowing the mixing of plasma between the two plasma regions. Occurrence of KH waves had been observed at Venus’ ionopause and the induced magnetopause, contributing to loss of planetary ions in the form of plasma clouds. Earlier simulations and observational studies have also explored the possibility of non-linear KH instability occurring at Mars. We will discuss the conditions required for the development of KH instability, its growth rate and implications on mass loss at Mars. Comparison with simulations will also be conducted and discussed.

How to cite: Poh, G., Espley, J., Romanelli, N., Gruesbeck, J., and DiBraccio, G.: MAVEN Observations of Large-amplitude, Quasi-periodic Sawtooth-like Magnetic Field Oscillations Associated with Kelvin-Helmholtz Instability , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12241, https://doi.org/10.5194/egusphere-egu2020-12241, 2020.

D2868 |
Marcin Pilinski, Laila Andersson, and Ed Thiemann

The MAVEN satellite has now made two Martian-years of ionosphere-thermosphere (I-T) observations enabling limited studies of seasonal changes in the upper atmosphere. Before examining the ionospheric dynamics associated with space weather, we wish to understand the climatological conditions of the system.  For example, previous studies have revealed the morning electron temperature overshoot as well as a close dependence between electron temperatures and neutral densities in the equatorial regions. In this presentation, we will examine differences in the northern and southern dayside ionosphere during the summer season of each hemisphere. The differences between these two cases will be contrasted with the seasonal dependence at the equator. Differences between the equatorial and polar regions are expected due to (A) differences in neutral scale heights, (B) differences in the solar zenith angle, and (C) the equilibration of I-T coupling due to differences in solar illumination.

In this work, we present a statistical analysis of MAVEN measurements comparing the north and south summer I-T. We find that when controlling for neutral pressure and latitude, the north and south plasma densities and temperatures are nearly identical below the demagnetization altitude (higher neutral pressures). Above the demagnetization altitude (lower neutral pressures), the southern hemisphere electron densities are higher than those in the northern hemisphere by ~100%. A significantly lower electron temperature is also observed in the south at these lower pressures. Given that the difference in solar EUV (and corresponding neutral heating) is ~20% between the two summer seasons, we postulate that the significantly lower plasma densities (above the demagnetization altitude) in the northern summer are due in part to an increase in ionospheric loss. This loss may be associated with the acceleration of ionospheric particles by the draped magnetic fields at an altitude where ions are not demagnetized. Furthermore, the loss may be diminished in the southern hemisphere where crustal magnetic fields increase the standoff distance to the solar wind magnetic field.

How to cite: Pilinski, M., Andersson, L., and Thiemann, E.: Hemispheric Asymmetry in the Mars Summer Ionosphere at Various Solar Forcing Conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12363, https://doi.org/10.5194/egusphere-egu2020-12363, 2020.

D2869 |
Beatriz Sanchez-Cano, Clara Narvaez, Mark Lester, Michael Mendillo, Majd Mayyasi, and Mats Holmstrom

The ionopause is a tangential discontinuity in the ionospheric thermal plasma density profile that marks the upper boundary of the ionosphere for unmagnetized planets. This interface is formed by a balance of pressures, as the ionopause is the region where the total pressure of the ionosphere (ionospheric thermal pressure plus magnetic pressure) balances the solar wind ram pressure. Since only Venus and Mars have no global “dipole” magnetic fields, ionopauses are unique to those planets. For Venus, the ionopause formation is well characterized because the thermal pressure of the ionosphere is usually larger than the solar wind dynamic pressure. For Mars, however, the maximum thermal pressure of the ionosphere is usually insufficient to balance the total pressure in the overlying magnetic pileup boundary. Therefore, the Martian ionopause is not always formed, and when it does, it is located at a large range of altitudes, varies rapidly and is highly structured. In this study, we characterise the Martian ionopause formation from the point of view of the thermal, magnetic and dynamic pressure balance. The objective of this paper is to assess under which circumstances the Martian ionopause is formed, both over and far from crustal magnetic fields. We focus on three MAVEN deep dip campaigns that occurred on the dayside of Mars, and we utilize several multi-plasma and magnetic field in-situ observations from the MAVEN mission, as well as solar wind plasma observations from the Mars Express mission.

How to cite: Sanchez-Cano, B., Narvaez, C., Lester, M., Mendillo, M., Mayyasi, M., and Holmstrom, M.: Mars’ ionopause: A game of pressures, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16452, https://doi.org/10.5194/egusphere-egu2020-16452, 2020.

D2870 |
Robert Lillis, Shannon Curry, Christopher Russell, Janet Luhmann, Aroh Barjatya, Davin Larson, Ronan Modolo, Roberto Livi, Phyllis Whittlesey, Yuki Harada, Christopher Fowler, Shaosui Xu, David Brain, Paul Withers, and Edward Thiemann

Multi-spacecraft missions after 2000 (Cluster II, THEMIS, Van Allen Probes, and MMS) have revolutionized our understanding of the causes, patterns and variability of a wide array of plasma phenomena in the terrestrial magnetospheric environment. ESCAPADE is a twin-spacecraft Mars mission concept that will similarly revolutionize our understanding of how solar wind momentum and energy flows throughout Mars’ magnetosphere to drive ion and sputtering escape, two processes which have helped shape Mars’ climate evolution over solar system history. 

ESCAPADE will measure magnetic field strength and topology, ion plasma distributions (separated into light and heavy masses), as well as suprathermal electron flows and thermal electron and ion densities, from elliptical, 200 km x 7000 km orbits. ESCAPADE are small spacecraft (<90 kg), traveling to Mars via solar electric propulsion as a rideshare with the Psyche metal-asteroid mission in August 2022, matching Mars’ heliocentric orbit until capture and spiral-down to science orbits. ESCAPADE’s strategically-designed 1-year, 2-part scientific campaign of temporally and spatially-separated multipoint measurements in different parts of Mars’ diverse plasma environment, will allow the cause-and-effect of solar wind control of ion and sputtering escape to be unraveled for the first time. Figure 1 shows ESCAPADE’s orbits within a hybrid simulation of the solar wind interaction with Mars, where the color scale represents ion velocity, blue lines are magnetic field, while white lines are sample proton trajectories and spacecraft orbits.

ESCAPADE has been selected for Phase A and B study by NASA as one of three finalists in the SIMPLEX-II program.  We will report on science goals, engineering and mission design challenges, and provide a status update.

How to cite: Lillis, R., Curry, S., Russell, C., Luhmann, J., Barjatya, A., Larson, D., Modolo, R., Livi, R., Whittlesey, P., Harada, Y., Fowler, C., Xu, S., Brain, D., Withers, P., and Thiemann, E.: ESCAPADE: coordinated multipoint measurements of Mars' near-space plasma environment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6354, https://doi.org/10.5194/egusphere-egu2020-6354, 2020.

D2871 |
Riku Jarvinen, Esa Kallio, and Tuija Pulkkinen

We study the solar wind interaction with Venus in a 3-dimensional global hybrid model where ions are treated as particles and electrons are a charge-neutralizing fluid. We concentrate on large-scale ultra-low frequency (ULF) waves in the ion foreshock and how they affect the energization and escape of planetary ions. The ion foreshock forms in the upstream region ahead of the quasi-parallel bow shock, where the angle between the shock normal and the magnetic field is smaller than about 45 degrees. The magnetic connection with the bow shock allows backstreaming of the solar wind ions leading to the formation of the ion foreshock. This kind of beam-plasma configuration is a source of free energy for the excitation of plasma waves. The foreshock ULF waves convect downstream with the solar wind flow and encounter the bow shock and transmit in the downstream region. We analyze the coupling of the ULF waves with the planetary ion acceleration and compare Venus and Mars in a global hybrid simulation.

How to cite: Jarvinen, R., Kallio, E., and Pulkkinen, T.: Modulation of the solar wind driven ion escape from unmagnetized planets by ultra-low-frequency foreshock waves in a global hybrid simulation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6891, https://doi.org/10.5194/egusphere-egu2020-6891, 2020.

D2872 |
Cyril Simon Wedlund, Martin Volwerk, Christian Mazelle, Christian Möstl, Diana Rojas-Castillo, Jared Espley, and Jasper Halekas

Ultra low-frequency wave activity such as mirror mode (MM) waves, arising from an ion temperature anisotropy in the plasma, has been ubiquitously detected in the magnetosheaths of Venus and Mars. The MM instability is usually triggered behind a quasi-perpendicular bow shock in a high plasma β. We present here a statistical survey of these waves at Mars using magnetometer and ion data from the NASA/MAVEN mission between 2014 and 2019 (solar cycle 24, receding activity). First, quasi-perpendicular bow shock crossings are identified in the data using simple bow shock models (Edberg et al. 2008, Gruesbeck et al. 2018, Hall et al. 2019). MM waves are then automatically detected for these conditions, first from magnetometer measurements only (in the manner of Volwerk et al., 2016), and second using both magnetometer and ion moments to refine the analysis. Maps of MM wave occurrence for solar cycle 24 are presented and preliminary comparisons with similar and different solar activity conditions with MGS and Mars Express data are discussed.

How to cite: Simon Wedlund, C., Volwerk, M., Mazelle, C., Möstl, C., Rojas-Castillo, D., Espley, J., and Halekas, J.: Statistical occurrence of mirror mode waves at Mars, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7497, https://doi.org/10.5194/egusphere-egu2020-7497, 2020.

D2873 |
Eduard Dubinin, Markus Fraenz, Marin Pätzold, Joachim Woch, Kai Fan, Yong Wei, Jim McFadden, Olga Tsareva, and Lev Zelenyi

Does an intrinsic field inhibits or enhances ion escape from planetary ionospheres is still an unsolved issue. Mars does not possess a global intrinsic magnetic field but instead has the strong crustal magnetic fields localized mainly in the southern hemisphere. The crustal magnetic field significantly influences the interaction of the solar wind with Mars adding features typical for planets with a global intrinsic magnetic field. Therefore it is interesting to compare ion losses from the ionosphere regions with and without strong crustal fields. Recently such studies were performed and have shown a protective effect of the crustal field on escape of the energized (E > 30 eV) oxygen ions (e.g. Fan et al., Geophysical Review Letters, 2019). However, the main bulk of escaping ions at Mars have energy lower than 30 eV. We will present the results of influence of the crustal magnetic field at Mars on the total losses of O+ and O2+ ions. The global picture of ion escape occurs more complex. Effects of larger ionospheric areas above the crustal field sources exposed by solar wind compensate a shielding effect at lower altitudes. As a result, the ion losses from the southern ionosphere of Mars might be even higher than losses from the northern “unmagnetized” ionosphere.

How to cite: Dubinin, E., Fraenz, M., Pätzold, M., Woch, J., Fan, K., Wei, Y., McFadden, J., Tsareva, O., and Zelenyi, L.: Crustal magnetic fields at Mars and ion escape, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7864, https://doi.org/10.5194/egusphere-egu2020-7864, 2020.

D2874 |
Aniko Timar, Zoltan Nemeth, Karoly Szego, Melinda Dósa, and Balazs Nagy

Rosetta observed medium-energy ions around comet 67P/Churyumov-Gerasimenko while orbiting deep inside the coma. These ions are thought to be accelerated towards the anti-sunward direction by some acceleration mechanism in the outer regions of the cometary magnetosphere. They usually reach energies up to 100-1000 eV and undergo deceleration in the dense neutral coma surrounding the nucleus. These ions usually appear in the ion dynamic spectrum as a new population rising from the low energy background, their energy peaking around 1000 eV and then decreasing until the population disappears again. We investigated the properties of these ions, as well as the relationship between the solar wind pressure and the energy of the medium-energy ions to discover the cause of the observed time variation. We show that there is a correlation between the solar wind dynamic pressure around the comet and the energy of the accelerated ions.

How to cite: Timar, A., Nemeth, Z., Szego, K., Dósa, M., and Nagy, B.: Effects of the solar wind dynamic pressure on the accelerated cometary ions in the magnetosphere of comet 67P, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9757, https://doi.org/10.5194/egusphere-egu2020-9757, 2020.

D2875 |
Christopher Fowler, Oleksiy Agapitov, Shaosui Xu, David Mitchell, Laila Andersson, Anton Artemyev, Jared Espley, Robert Ergun, and Christian Mazelle

We present Mars Atmosphere and Volatile EvolutioN (MAVEN) observations of periodic (~ 25 s) large scale (100s km) magnetosonic waves propagating into the Martian dayside upper ionosphere. These waves adiabatically modulate the superthermal electron distribution function, and the induced electron temperature anisotropies drive the generation of observed electromagnetic whistler waves. The localized (in altitude) minimum in the ratio fpe / fce provides conditions favorable for the local enhancement of efficient wave-particle interactions, so that the induced whistlers act back on the superthermal electron population to isotropize the plasma through pitch angle scattering. These wave-particle interactions break the adiabaticity of the large scale magnetosonic wave compressions, leading to local heating of the superthermal electrons during compressive wave `troughs'. Further evidence of this heating is observed as the subsequent phase shift between the observed perpendicular-to-parallel superthermal electron temperatures and compressive wave fronts. Such a heating mechanism may be important at other unmagnetized bodies such as Venus and comets.

How to cite: Fowler, C., Agapitov, O., Xu, S., Mitchell, D., Andersson, L., Artemyev, A., Espley, J., Ergun, R., and Mazelle, C.: Localized heating of the Martian topside ionosphere through the combined effects of magnetic pumping by large scale magnetosonic waves and pitch angle diffusion by whistler waves, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10492, https://doi.org/10.5194/egusphere-egu2020-10492, 2020.

D2876 |
Xiao-Dong Wang and Shahab Fatemi

We report the preliminary results of a hybrid simulation to differentiate and quantify the energy gain due to different electric field terms in the acceleration of planetary ions escaping from an induced magnetosphere. 

The planetary ions gain energy from the electric field formed in the induced magnetosphere. The electric field is not directly measurable and thus has to be expressed by the generalized Ohm's law with measurable quantities:

E = -Ve×B - ∇Pe/(qene) + j×B/(qene)

Where Ve is the velocity of the electrons that freeze the magnetic field B, Pe is the thermal pressure tensor, and j is the Hall current. The three terms on the right-hand side describe the three different mechanisms of ion acceleration: the motional term, the pressure gradient term, and the Hall term. All these terms contribute to the energization of escaping ions, while they dominate in different positions in an induced magnetosphere, and play different roles in the dynamics of an escaping ion.

We will quantify the energy gain due to each electric field term of escaping ions depending on the birthplaces of the ions. Our tool is AMITIS, a GPU-based 3-D hybrid code (ions as particles and electrons as a fluid) to model the plasma interaction with a planet (Fatemi et al., 2017). For a test, we simulated the solar wind interaction with Mars at nominal space environment conditions until a quasi-steady state. We calculated different electric field terms and compared them with the MAVEN measurements. The simulation results show good agreement with measurements in both magnitude and spatial distribution.


We further launched test particles from different positions in the ionosphere and tracked the energy gain/loss due to different electric field terms along their escaping trajectories. The energization history of an ion depends on its trajectory, which further partly depends on the birthplace of the ion. Ions produced outside of the IMB are accelerated or “picked up” totally by the motional electric field. Ions produced in the induced magnetosphere in the dayside may be accelerated by the thermal pressure gradient of the ionosphere, while those produced in the nightside are driven more by the Hall electric field.

How to cite: Wang, X.-D. and Fatemi, S.: Acceleration of Planetary Ions by Different Electric Field Terms in an Induced Magnetosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11419, https://doi.org/10.5194/egusphere-egu2020-11419, 2020.

D2877 |
Junfeng Qin, Hong Zou, Yuguang Ye, Jinsong Wang, and Erling Nielsen

It has been clear that the main cause of Martian deep-nightside ionosphere is electron precipitation, which is dominated by Martian crustal magnetic field. In this research, the dependence of deep-nightside Martian ionosphere TEC (Total Electron Content) on crustal magnetic field was studied based on Martian ionospheric TEC data from MEX/MARSIS and 400km crustal magnetic field data from MGS. It is found that the strength and inclination of crustal magnetic field have great effects on Martian deep-nightside ionospheric TEC. This kind of effects are worth to be compared with the effects of crustal magnetic field on electron precipitation studied in previous researches (such as Lillis and Brain, 2013, Nightside electron precipitation at Mars: Geographic variability and dependence on solar wind conditions) to find out more about the formation of Martian deep-nightside ionosphere. It is also found that, in a Martian crustal magnetic field cusp region, the observed deep-nightside ionospheric TECs in the center of the cusp are lower than those in the edge of the cusp, a phenomenon not noticed before. It indicates that there may be more precipitated electrons moving along the closed crustal magnetic lines than moving along open crustal magnetic lines, and these precipitated electrons in closed magnetic lines can be related to the energy processes in the nightside of Mars, such as magnetic reconnections.

How to cite: Qin, J., Zou, H., Ye, Y., Wang, J., and Nielsen, E.: The dependence of deep-nightside Martian ionosphere TEC on crustal magnetic field, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13746, https://doi.org/10.5194/egusphere-egu2020-13746, 2020.

D2878 |
Stas Barabash, Andrii Voshchepynets, Mats Holmström, Futaana Yoshifumi, and Robin Ramstad

Induced magnetospheres of non-magnetized atmospheric bodies like Mars and Venus are formed by magnetic fields of ionospheric currents induced by the convective electric field E = - V x B/c of the solar wind. The induced magnetic fields create a magnetic barrier which forms a void of the solar wind plasma, an induced magnetosphere. But what happens when the interplanetary magnetic field is mostly radial and the convective field E ≈ 0? Do a magnetic barrier and solar wind void form? If yes, how such a degenerate induced magnetosphere work? The question is directly related to the problem of the atmospheric escape due to the interaction with the solar and stellar winds. The radial interplanetary magnetic field in the inner solar system is typical for the ancient Sun conditions and exoplanets on near-star orbits. Also, the radial interplanetary field may provide stronger coupling of the near-planet environment with the solar/stellar winds and thus effectively channels the solar/stellar wind energy to the ionospheric ions. We review the current works on the subject, show examples of degenerate induced magnetospheres of Mars and Venus from Mars Express, Venus Express, and MAVEN measurements and hybrid simulations, discuss physics of degenerate induced magnetospheres, and impact of such configurations on the escape processes.

How to cite: Barabash, S., Voshchepynets, A., Holmström, M., Yoshifumi, F., and Ramstad, R.: Degenerate induced magnetospheres, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13754, https://doi.org/10.5194/egusphere-egu2020-13754, 2020.

D2879 |
Mark Lester, Beatriz Sanchez-Cano, Hannah Biddle, Daniel Potts, Pierre-Louis Blelly, Hermann Opgenoorth, Olivier Witasse, Marco Cartacci, Roberto Orosei, Fabrizio Bernardini, Nathaniel Putzig, Bruce Campbell, Robert Lillis, François Leblanc, Steve Milan, and John M.C. Plane

The loss of signal detection by the sub surface radars currently operational on Mars Express and Mars Reconnaissance Orbiter can be evidence of enhanced ionisation at lower altitudes in the Martian atmosphere as a result of solar energetic particles penetrating to these altitudes.  The MARSIS instrument on Mars Express and SHARAD on MRO operate at different frequencies, with MARSIS up to 5 MHz and SHARAD between 10 and 20 MHZ.  In addition MARSIS can operate in an additional mode as an Active Ionospheric Sounder, although here we focus only on the sub surface mode.  We present an analysis of the data during the lifetimes of both instruments, extending from 2005 to 2018.  Here we identify the radar blackouts as either total or partial and investigate their occurrence as a function of solar cycle.  We find a clear solar cycle dependence with more events occurring during the solar maximum years, as expected.  However, we also note the duration of events is often much longer than expected, in excess of several days, sometimes reaching 10 – 14 days.  Investigation of other data sets, notably from the MAVEN SEP instrument complements the analysis.  We finally compare our observations at Mars with similar observations at Earth.

How to cite: Lester, M., Sanchez-Cano, B., Biddle, H., Potts, D., Blelly, P.-L., Opgenoorth, H., Witasse, O., Cartacci, M., Orosei, R., Bernardini, F., Putzig, N., Campbell, B., Lillis, R., Leblanc, F., Milan, S., and Plane, J. M. C.: A Statistical Analysis of Radar Blackout Events at Mars, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16717, https://doi.org/10.5194/egusphere-egu2020-16717, 2020.

D2880 |
Yulia Izvekova, Sergey Popel, and Alina Besedina

A self-consistent consideration of the motion of dust particles in plasma systems in the atmosphere of Mars can lead to the detection of oscillations and waves, which, in particular, can be detected from the surface of the planet. The presence of local magnetic fields leads to significant inhomogeneities in the ionosphere of Mars, especially noticeable on the night side. On the night side of the ionosphere, there are areas of sharp increase in electron concentrations in areas where the lines of force of the magnetic field are perpendicular to the surface of the planet. In the areas where the magnetic field is parallel to the surface, the electrons of the solar wind do not penetrate the atmosphere and there is no ionization. Horizontal gradients of electron density on the night side can exceed 10 ^ 4 cm ^ -3 for several tens of kilometers. Such high plasma density gradients lead to local plasma transfer perpendicular to the external magnetic field, horizontal currents and electric fields are generated. Interaction of the plasma of the solar wind with a plasma containing dust particles can lead to the generation of high-frequency waves.

The work is supported by the Russian Science Foundation (project No 18-72-00119).

How to cite: Izvekova, Y., Popel, S., and Besedina, A.: Dusty plasma effects in the nighttime ionosphere of mars, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17083, https://doi.org/10.5194/egusphere-egu2020-17083, 2020.

D2881 |
Andrii Voshchepynets, Stas Barabash, Mats Holmstrom, Rudy Frahm, and Andrew Kopf

We report the first observations of sounder accelerated particles (SAP) in the ionosphere of a planet which does not possess a strong magnetic field (Mars). These observations were conducted onboard the Mars Express spacecraft by the ion and electron sensors of the Analyzer of Space Plasmas and Energetic Atoms (ASPERA-3) experiment and the powerful topside sounder: Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS). Accelerated ions (O2+ , O+, and lighter ions) are observed in an energy range up to 800 eV when MARSIS transmits at a frequency close to the plasma frequency. Individual observations consist of almost monoenergetic ion beams either aligned with the MARSIS antenna or lying in the perpendicular plane. The observed ion beams are often accompanied by a decrease in the electron flux. Accelerated electrons are observed at energies up to 400 eV when MARSIS transmits at a frequency between the local plasma frequency and its harmonics (up to four times the plasma frequency). The majority of the sounder accelerated electrons are recorded close to the regions of intense crustal magnetic fields. The voltage applied to the MARSIS antenna causes spacecraft charging to 100’s of volts by electrons from the ambient plasma. Positively charged ions are accelerated when the spacecraft discharges. Accelerated photoelectrons are released by the highly charged spacecraft and after one gyration in the strong magnetic field, return to the spacecraft which has already discharged. The acceleration effect influences which ions can be observed by increasing the energy of the thermal ion species making it possible to detect them whereas they would be indistinguishable under normal circumstances. We present the relevant data and discuss how these effects can be used for diagnostic of the local plasma.

How to cite: Voshchepynets, A., Barabash, S., Holmstrom, M., Frahm, R., and Kopf, A.: Sounder Accelerated Particles at Mars: Observations, Mechanisms, and Applications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18500, https://doi.org/10.5194/egusphere-egu2020-18500, 2020.

D2882 |
Simon A. Pope and Michael A. Balikhin

A new type of very-low Mach number shock in which the primary method of energy re-distribution is the kinematic relaxation of a non-gyrotropic ion population, was discovered at Venus early in the Venus Express mission. This led to the development of an associated theory and numerical analysis. The recent discovery of such a shock at the Earth using THEMIS data experimentally verified this theory using simultaneous magnetic field and plasma data. It also showed that the most favourable conditions for the formation of such a shock is the magnetic cloud phase of an ICME. Venus Express provides an excellent opportunity to study such shocks further. Here we present results from the duration of the mission, which identifies over thirty shock crossings showing evidence of kinematic relaxation. These shock crossings are investigated to understand how the upstream conditions and heavy ions (including pick-up ions) affect their formation.

How to cite: Pope, S. A. and Balikhin, M. A.: A study of kinematic relaxation at the Venus bow shock, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19305, https://doi.org/10.5194/egusphere-egu2020-19305, 2020.

D2883 |
Elias Odelstad, Tomas Karlsson, and Anders Eriksson
The plasma environments of active comets are dominated by the interaction of the solar wind with newly born cometary heavy ions, predominantly water group ions produced by ionization of cometary neutral volatiles over large distances in the extensive and diffuse cometary coma. The resulting vast comet-solar wind interaction region hosts a plethora of plasma instabilities, waves and turbulence phenomena, and thus constitutes a formidable natural laboratory for studying such processes.
Waves are also important in determining many of the plasma properties of this environment. They can, e.g., heat or cool plasma populations, create supra-thermal electrons responsible for X-ray emissions, reduce plasma anisotropies and gradients, couple different plasma species, and provide anomalous resistivity.
Electric field measurements in the cometary plasma environment have until recently been rare, and have only been performed during short fly-by missions, at relatively large distances from the comet nucleus. The electric field measurements by the LAP instrument onboard the Rosetta spacecraft, collected during more than two years in the vicinity of comet 67P/Churyumov-Gerasimenko therefore represent a truly unique data set.
We use the database of 60 Hz electric field measurements of waves in the lower-hybrid frequency range, and correlate the comet-related parameters, (relative spacecraft position, solar distance, plasma and neutral gas density, etc.) with wave related parameters, such as amplitude/spectral density and frequency. We also compare statistically the properties of the waves with theoretical predictions of lower-hybrid wave generation, regarding e.g. amplitude dependence on plasma density gradients, with the aim of clarifying the importance of the plasma waves in different regions of the cometary plasma environment.
Electric field measurements allow investigating both electrostatic wave modes and electromagnetic ones. We investigate frequencies and amplitudes of the electric field oscillations and use background magnetic field values and plasma properties to determine relevant expected frequencies, as well as magnetic field oscillations (for low and medium frequencies) to determine if the plasma waves are electrostatic or electromagnetic. Lower hybrid waves are almost electrostatic, but have a small magnetic field signature from second order effects. Determination of the most common wave modes gives an indication of the role of plasma waves in the cometary plasma environment probed by Rosetta.
Lower hybrid waves are common in the inner coma of 67P. Such waves are predicted to energize electrons parallel to the ambient magnetic field, and ions in the perpendicular direction. With the help of ion and electron data, we test this prediction, which may explain the presence of a hot electron population reported on, but of hitherto unknown origin. These results give clues to the role of the waves in the formation of the cometary plasma environment.

How to cite: Odelstad, E., Karlsson, T., and Eriksson, A.: Rosetta electric field observations in the plasma environment of comet 67P/Churyumov-Gerasimenko, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20178, https://doi.org/10.5194/egusphere-egu2020-20178, 2020.

D2884 |
Yingjuan Ma, Chris Russell, Yanan Yu, Andrew Nagy, Gabor Toth, and Bruce Jakosky2

The Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) mission was launched on 5 May 2018 and successfully landed at Elysium Planitia (4.5oN, 135.9oE)on Mars on 26 November 2018. The InSight Lander carries a magnetometer to measure disturbances from the Martian ionosphere. In order to understand the daily variations in the magnet field measurements on Martian surface, in this study, we use the time-dependent MHD model to study how plasma conditions vary with local time above insight landing site using solar wind condition from MAVEN observation. Significant diurnal variations can be seen in all plasma quantities due to solar wind interactions and planetary rotation. The induced magnetic field is mainly in the same direction as the upstream IMF. However, it seems that the variations seen by the Insight magnetometer cannot be only due to the interaction of the solar wind. We also add a neutral wind effect in our simulations to further investigate possible causes of surface field changes.

How to cite: Ma, Y., Russell, C., Yu, Y., Nagy, A., Toth, G., and Jakosky2, B.: MHD Predictions of Plasma Conditions Above Insight Landing Site based on MAVEN observations , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20751, https://doi.org/10.5194/egusphere-egu2020-20751, 2020.

D2885 |
Antonio Renzaglia, Thomas Cravens, Christopher Fowler, Ali Rahmati, Shotaro Sakai, Jack Connerney, Mehdi Benna, and Laila Andersson

NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) explorer has been in orbit around Mars for over 5 years now, collecting valuable data about the planet. Specifically, the Langmuir Probe and Waves (LPW), the Neutral Gas and Ion Mass Spectrometer (NGIMS), and the Suprathermal and Thermal Ion Composition (STATIC) instruments measure important ionospheric properties. The instruments measure electron densities and temperature (LPW), neutral gas and ion composition (NGIMS), and the properties of escaping ions (STATIC). Electron and ion density and flux measurements are presented. The data indicates significant differences in ion properties between open crustal, closed crustal, and draped magnetic fields. Similar differences are noted for electrons as well. An ionospheric model has been developed that produces a profile of the ionosphere. The model then explores the evolution of the ionosphere, via chemistry and transport. At low altitudes (z<300 km), chemistry dominates, while transport dominates at higher altitudes. Results show significant differences in the ionosphere between the types of fields. The model utilizes data from the Magnetometer (MAG) instrument to provide properties of magnetic fields at Mars. The model may also help explain some of the atmospheric loss occurring at Mars. This is compared to data from STATIC. Analytic arguments for subsonic vs supersonic flow speeds (in the open field case) are also presented.

How to cite: Renzaglia, A., Cravens, T., Fowler, C., Rahmati, A., Sakai, S., Connerney, J., Benna, M., and Andersson, L.: Modeling Ionospheric Densities and Flows in Crustal and Draped Magnetic Fields at Mars, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20922, https://doi.org/10.5194/egusphere-egu2020-20922, 2020.