Flows, Fields, and Forces in the Mars‐Solar Wind Interaction

Halekas, J. S.; Brain, David; Luhmann, J. G.; DiBraccio, G. A.; Ruhunusiri, S.; Harada, Yuki; Fowler, C. M.; Mitchell, David; Connerney, J. E. P.; Espley, J. R.; Mazelle, C.; Jakosky, B. M.

doi:10.1002/2017ja024772

Cited by 93 publications

(182 citation statements)

References 74 publications

(104 reference statements)

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“…The pressure gradient force in the Z direction is negligible near the equatorial plane. The ion pressure gradient force predicted by the model is consistent with that derived from MAVEN plasma observations (Halekas et al, ).…”

Section: Simulation Resultssupporting

confidence: 84%

Importance of Ambipolar Electric Field in Driving Ion Loss From Mars: Results From a Multifluid MHD Model With the Electron Pressure Equation Included

Dong

Tóth

et al. 2019

JGR Space Physics

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The multifluid (MF) magnetohydrodynamic model of Mars is improved by solving an additional electron pressure equation. Through the electron pressure equation, the electron temperature is calculated based on the effects from various electron-related heating and cooling processes (e.g., photoelectron heating, electron-neutral collision, and electron-ion collision), and thus, the improved model can calculate the electron temperature and the electron pressure force terms self-consistently. Model results of a typical case using the MF with electron pressure equation included model are compared in detail to identical cases using the MF and multispecies models to identify the effect of the improved physics. We find that when the electron pressure equation is included, the general interaction patterns are similar to those with no electron pressure equation. However, the MF with electron pressure equation included model predicts that the electron temperature is much larger than the ion temperature in the ionosphere, consistent with both Viking and Mars Atmosphere and Volatile EvolutioN (MAVEN) observations. Using our numerical model, we also examined in detail the relative importance of different forces in the plasma interaction region. All three models are also applied to a MAVEN event study using identical input conditions; overall, the improved model matches best with MAVEN observations. All of the simulation cases are examined in terms of the total ion loss, and the results show that the inclusion of the electron pressure equation increases the escape rates by 50-110% in total mass, depending on solar condition and strong crustal field orientation, clearly demonstrating the importance of the ambipolar electric field in facilitating ion escape. Key Points:• For the first time, the effect of the ambipolar electric field is self-consistently included in the global multifluid MHD model • The ambipolar electric field plays a significant role in driving ion loss from Mars. The ion mass loss can be enhanced by more than 50% • The improved model matches best with MAVEN observations in comparison with previous models Supporting Information:• Supporting Information S1

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Section: Simulation Resultssupporting

confidence: 84%

Importance of Ambipolar Electric Field in Driving Ion Loss From Mars: Results From a Multifluid MHD Model With the Electron Pressure Equation Included

Dong

Tóth

et al. 2019

JGR Space Physics

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“…We obtain transverse wave occurrence rates of 0.32% on the dawnside and 0.55% on the duskside from the data obtained at altitudes below 3,000 km in the nominal magnetosheath region. We note that higher proton temperature anisotropy is observed by SWIA in the quasi‐perpendicular magnetosheath (Halekas et al, ), and we obtained similar results from STATIC data (not shown).…”

Section: Statistical Resultssupporting

confidence: 89%

Locally Generated ULF Waves in the Martian Magnetosphere: MAVEN Observations

et al. 2019

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We investigate Martian ultralow frequency (ULF) electromagnetic waves generated by local plasma instabilities below the Martian bow shock. Recent Mars Atmosphere and Volatile EvolutioN (MAVEN) observations have shown that ULF waves generated upstream of the Martian bow shock can propagate down to the upper ionosphere, possibly facilitating heavy ion escape from Mars by heating the ionospheric plasma. In contrast to the upstream waves oscillating near the upstream proton cyclotron frequency, we identify narrow band ULF magnetic field fluctuations with frequencies near the local proton cyclotron frequency (f cp(local) ) from MAVEN data. In addition to expected proton cyclotron waves locally generated in the magnetosheath, we newly identify compressional narrow band emissions near f cp(local) (and its harmonics for some cases) in the dayside upper ionosphere and in the nightside magnetotail. The dayside waves are preferentially observed for high solar extreme ultraviolet (EUV) conditions and are often associated with ring/shell-like, hot protons of magnetosheath origin in the presence of cold, dense ionospheric protons. The nightside waves exhibit distinct preference for high-solar-EUV, strong-solar-wind conditions, under which both warm and cold protons are enhanced. The observed properties of these compressional waves are generally consistent with a proton Bernstein mode instability driven by a positive perpendicular slope in proton velocity distribution functions. The excited waves can cause perpendicular heating of thermal protons, thereby transferring energy from precipitating hot protons to cold ionospheric protons.

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“…Reducing this threshold leads to more positive events but at the expense of an increased risk of detecting random variations that are not MHs. The backstreaming ions move sunward in the solar wind frame with velocities in the order of a few Alfvén speed and interact with the incident solar wind, driving nonlinear ion-ion instabilities that lead to generation of ultralow frequency waves (Gary et al, 1981;Gary, 1993;Hoppe & Russell, 1983;Halekas, Brain, et al, 2017;Mazelle et al, 1991). Criterion 3 eliminates step-like events, which commonly occur during shock crossings, foreshock compressional boundaries, and Short Large Amplitude Magnetic Structures Omidi et al, 2009;Schwartz & Burgess, 1991).…”

Section: Event Identificationmentioning

confidence: 99%

Magnetic Holes Upstream of the Martian Bow Shock: MAVEN Observations

et al. 2020

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Magnetic holes (MHs) are pressure-balanced structures characterized by distinct decreases in the interplanetary magnetic field strength in otherwise unperturbed solar wind. In this paper we present an analysis of MHs upstream of the Martian bow shock based on 3 months of observations by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. Plasma properties within and around these structures as well as their shape characteristics are examined. We find an occurrence rate of around 2.1 events per day. About 51% of all events are of linear type with magnetic field rotation across the hole less than 10 • . We observe linear MHs both as isolated events and as part of a train of MHs. The proton temperature anisotropy inside MHs increases, while alpha particles remain mostly isotropic. The average electron temperature inside MHs modestly increases with increasing hole depth. The duration of linear holes at 1.5 AU shows an increase compared to durations at smaller heliocentric distances, but the structures remain asymmetrical and ellipsoid. A case study of MHs accompanied by a population of heavy pickup ions is also discussed. Plain Language SummaryThe solar wind, a supersonic flow of electrons and ions flowing radially outward from the Sun, carries a magnetic field. Magnetic holes are structures with reduced magnetic field strength that last between a few seconds to a few minutes. These structures have been observed at many places throughout the solar system. A common formation mechanism for magnetic holes is a wave mode instability that converts magnetic energy into ion thermal energy, known as the mirror mode. Mirror mode instabilities grow when the temperature of ions moving perpendicular to the magnetic field is higher than that of ions moving in the parallel direction. Mirror waves alter the magnetic field and the spatial structure of the plasma. In this paper, we use observations from the Mars Atmosphere and Volatile EvolutioN spacecraft to study magnetic holes in the space environment around Mars.

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Flows, Fields, and Forces in the Mars‐Solar Wind Interaction

Cited by 93 publications

References 74 publications

Importance of Ambipolar Electric Field in Driving Ion Loss From Mars: Results From a Multifluid MHD Model With the Electron Pressure Equation Included

Importance of Ambipolar Electric Field in Driving Ion Loss From Mars: Results From a Multifluid MHD Model With the Electron Pressure Equation Included

Locally Generated ULF Waves in the Martian Magnetosphere: MAVEN Observations

Magnetic Holes Upstream of the Martian Bow Shock: MAVEN Observations

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