Yingjuan Ma

Three-dimensional, multispecies, high spatial resolution MHD studies of the solar wind interaction with Mars

[1] We present the results of model calculations, using our new, four-species, spherical MHD model. Our results are compared with the relevant and limited available data. The resulting comparisons help us to increase our understanding of the interaction processes between the solar wind and the Martian atmosphere/ionosphere. This new model with a spherical grid structure allowed us to use small (� 10 km) radial grid spacing in the ionospheric region. We found that the calculated bow shock positions agree reasonably well with the observed values. The calculated results vary with interplanetary magnetic field orientation, solar cycle conditions, and subsolar location. We found that our calculated ion densities, with parameters corresponding to solar cycle minimum conditions, reproduced the Viking 1 observed ion densities well. The calculated solar cycle maximum densities, above � 140 km, are also consistent with the appropriate Mars Global Surveyor radio occultation electron densities. Both the calculated solar cycle maximum and solar cycle minimum total transterminator and escape fluxes are significantly smaller than our previously published values. This decrease is due to the improved temperature values used for the recombination rates in this new model, which in turn results in lower ion densities and lower fluxes. INDEX TERMS: 2780 Magnetospheric Physics: Solar wind interactions with unmagnetized bodies; 6026 Planetology: Comets and Small Bodies: Ionospheres— composition and chemistry; 6028 Planetology: Comets and Small Bodies: Ionospheres—structure and dynamics; 2728 Magnetospheric Physics: Magnetosheath; KEYWORDS: Mars, MHD, bow shock, ionosphere, solar wind interaction

Three‐dimensional multispecies MHD studies of the solar wind interaction with Mars in the presence of crustal fields

interaction of the solar wind with Mars. The three ions considered are H + ,O 2 , and O + , representing the solar wind and the two major ionospheric ion species, respectively. The calculations indicate that the presence of a hot oxygen corona does not, within the resolution and accuracy of the model, lead to any significant effect on the dayside bow shock and ionopause positions. Next the trans-terminator fluxes and escape fluxes down the tail were calculated neglecting the effects of the crustal magnetic field. The calculated flux values are consistent with the measured escape fluxes and the calculated limiting fluxes from the dayside ionosphere. Finally, a 60-order harmonic expansion model of the measured magnetic field was incorporated into the model. The crustal magnetic field did not cause major distortions in the bow shock but certainly had an important effect within the magnetosheath and on the apparent altitude of the ionopause. The model results also indicated the presence of ‘‘minimagnetocylinders,’’ consistent with the MGS observations. We also recalculated the trans-terminator and escape fluxes, for the nominal solar wind case, in the presence of the crustal magnetic field and found, as expected, that there is a decrease in the calculated escape flux; however, it is still reasonably close to the value estimated from the Phobos-2 observations. INDEX TERMS: 2780 Magnetospheric Physics: Solar wind interactions with unmagnetized bodies; 2459 Ionosphere: Planetary ionospheres (5435, 5729, 6026, 6027, 6028); 5440 Planetology: Solid Surface Planets: Magnetic fields and magnetism; 2728 Magnetospheric Physics: Magnetosheath; KEYWORDS: Mars, MHD, bow shock, escape flux, solar wind interaction, crustal magnetic field Citation: Ma, Y., A. F. Nagy, K. C. Hansen, D. L. DeZeeuw, T. I. Gombosi, and K. G. Powell, Three-dimensional multispecies MHD studies of the solar wind interaction with Mars in the presence of crustal fields, J. Geophys. Res., 107(A10), 1282, doi:10.1029/2002JA009293, 2002.

The spatial distribution of planetary ion fluxes near Mars observed by MAVEN

We present the results of an initial effort to statistically map the fluxes of planetary ions on a closed surface around Mars. Choosing a spherical shell ~1000 km above the planet, we map both outgoing and incoming ion fluxes (with energies >25 eV) over a 4 month period. The results show net escape of planetary ions behind Mars and strong fluxes of escaping ions from the northern hemisphere with respect to the solar wind convection electric field. Planetary ions also travel toward the planet, and return fluxes are particularly strong in the southern electric field hemisphere. We obtain a lower bound estimate for planetary ion escape of ~3 × 1024 s−1, accounting for the ~10% of ions that return toward the planet and assuming that the ~70% of the surface covered so far is representative of the regions not yet visited by Mars Atmosphere and Volatile EvolutioN (MAVEN).

Three-dimensional, multifluid, high spatial resolution MHD model studies of the solar wind interaction with Mars

[1] Our newly developed 3‐D, multifluid MHD model is used to study the interaction of the solar wind with Mars. This model is based on the BATS‐R‐US code, using a spherical grid and a radial resolution equal to 10 km in the ionospheric regions. We solve separate continuity, momentum, and energy equations for each ion fluid and run our model for both solar minimum and maximum conditions. We obtain asymmetric densities, velocities, and magnetic pileup in the plane containing both the direction of the solar wind and the convective electric field. These asymmetries are the result of the decoupling of the individual ions; therefore, our model is able to account for the respective dynamics of the ions and to show new physical processes that could not be observed by the single‐fluid model. Our results are consistent with the measured bow shock and magnetic pileup locations and with the Viking‐observed ion densities. We also compute the escape fluxes for both solar minimum and solar maximum conditions and compare them to the single‐fluid results and the observed values from Mars Express.

Pickup oxygen ion velocity space and spatial distribution around Mars

[1] We report a newly created highly parallelized global test particle model for resolving the pickup oxygen ion distribution around Mars. The background magnetic and convection electric fields are calculated using a three-dimensional multispecies magnetohydrodynamic model, which includes the effect of the Martian crustal magnetic field. In addition to photo-ionization, charge exchange collisions and solar wind electron impact ionization are included for the pickup ion generation. The most novel feature of our model is that more than one billion test particles are launched in the simulation domain in total. This corresponds to a profound enhancement by at least 3 orders of magnitude in the total number, compared to all existing test particle models. This substantial improvement enables an unprecedented examination of the pickup ion flux distribution in velocity space, which is not achievable in previous simulation studies due to the insufficient statistics arising from the limited number of test particles. Using the velocity space distribution of pickup O + ions as a tool, the Mars-solar wind interaction can be investigated in a unique way. It is shown that the velocity space distribution is highly non-Maxwellian, exhibiting non-gyrotropic and non-symmetric distributions, including many beam-like features. In the tail region, pickup ions have a prominent outflowing component in the whole energy range. The energy examination of particles traveling across the tail region shows that the acceleration highly depends on the source region where the particles originate. The strong convection electric field in the magnetosheath region is favorable to the pickup ion acceleration.

Solar wind interaction with Mars upper atmosphere: Results from the one‐way coupling between the multifluid MHD model and the MTGCM model

The 3-D multifluid Block Adaptive Tree Solar-wind Roe Upwind Scheme (BATS-R-US) MHD code (MF-MHD) is coupled with the 3-D Mars Thermospheric general circulation model (MTGCM). The ion escape rate from the Martian upper atmosphere is investigated by using a one-way coupling approach, i.e., the MF-MHD model incorporates the effects of 3-D neutral atmosphere profiles from the MTGCM model. The calculations are carried out for two cases with different solar cycle conditions. The calculated total ion escape flux (the sum of three major ionospheric species, O+, O2+, and CO2+) for solar cycle maximum conditions (6.6×1024 s−1) is about 2.6 times larger than that of solar cycle minimum conditions (2.5×1024 s−1). Our simulation results show good agreement with recent observations of 2–3×1024 s−1 (O+, O2+, and CO2+) measured near solar cycle minimum conditions by Mars Express. An extremely high solar wind condition is also simulated which may mimic the condition of coronal mass ejections or corotating interaction regions passing Mars. Simulation results show that it can lead to a significant value of the escape flux as large as 4.3×1025s−1.

Effects of crustal field rotation on the solar wind plasma interaction with Mars

The crustal remnant field on Mars rotates with the planet at a period of 24 h 37 min, constantly varying the magnetic field configuration interacting with the solar wind. Until now, there has been no self-consistent modeling investigation on how this varying magnetic field affects the solar wind plasma interaction. Here we include the rotation of this localized crustal field in a multispecies single-fluid MHD model of Mars and simulate an entire day of solar wind interaction under normal solar wind conditions. The MHD model results are compared with Mars Global Surveyor (MGS) magnetic field observations and show very close agreement, especially for the field strength along almost all of the 12 orbits on the day simulated. Model results also show that the ion escape rates slowly vary with rotation, generally anticorrelating with the strength of subsolar magnetic crustal sources, with some time delay. In addition, it is found that in the intense crustal field regions, the densities of heavy ion components enhance significantly along the MGS orbit, implying strong influence of the crustal field on the ionospheric structures.

Hall magnetohydrodynamics on block-adaptive grids

We present a conservative second order accurate finite volume discretization of the magnetohydrodynamics equations including the Hall term. The scheme is generalized to three-dimensional block-adaptive grids with Cartesian or generalized coordinates. The second order accurate discretization of the Hall term at grid resolution changes is described in detail. Both explicit and implicit time integration schemes are developed. The stability of the explicit time integration is ensured by including the whistler wave speed for the shortest discrete wave length into the numerical dissipation, but then second order accuracy requires the use of symmetric limiters in the total variation diminishing scheme. The implicit scheme employs a Newton-Krylov-Schwarz type approach, and can achieve significantly better efficiency than the explicit scheme with an appropriate preconditioner. The second order accuracy of the scheme is verified by numerical tests. The parallel scaling and robustness are demonstrated by three-dimensional simulations of planetary magnetospheres.

3‐D global MHD model prediction for the first close flyby of Titan by Cassini

[1] The global features of the interaction between Saturn’s magnetospheric plasma flow and Titan’s atmosphere/ ionosphere are simulated by using a 3-D, multi-species, high spatial resolution, global MHD model. Our model uses a spherical grid structure leading to very good (36 km) altitude resolution in the ionospheric region of Titan. The model also provides good resolution and meaningful results in the upstream and wake regions. Titan’s atmosphere and ionosphere are approximated by 10 neutral and 7 ion species. Calculations, which make predictions for the anticipated results to be obtained by the Cassini spacecraft during its first close flyby (TA) of Titan, are presented. INDEX TERMS: 2427 Ionosphere: Ionosphere/ atmosphere interactions (0335); 2732 Magnetospheric Physics: Magnetosphere interactions with satellites and rings; 2753 Magnetospheric Physics: Numerical modeling. Citation: Ma, Y.-J., A. F. Nagy, T. E. Cravens, I. V. Sokolov, J. Clark, and K. C. Hansen (2004), 3-D global MHD model prediction for the first close flyby of Titan by Cassini, Geophys. Res. Lett., 31, L22803,

Solar wind interaction with the Martian upper atmosphere: Crustal field orientation, solar cycle, and seasonal variations

A comprehensive study of the solar wind interaction with the Martian upper atmosphere is presented. Three global models: the 3-D Mars multifluid Block Adaptive Tree Solar-wind Roe Upwind Scheme MHD code (MF-MHD), the 3-D Mars Global Ionosphere Thermosphere Model (M-GITM), and the Mars exosphere Monte Carlo model Adaptive Mesh Particle Simulator (M-AMPS) were used in this study. These models are one-way coupled; i.e., the MF-MHD model uses the 3-D neutral inputs from M-GITM and the 3-D hot oxygen corona distribution from M-AMPS. By adopting this one-way coupling approach, the Martian upper atmosphere ion escape rates are investigated in detail with the combined variations of crustal field orientation, solar cycle, and Martian seasonal conditions. The calculated ion escape rates are compared with Mars Express observational data and show reasonable agreement. The variations in solar cycles and seasons can affect the ion loss by a factor of ∼3.3 and ∼1.3, respectively. The crustal magnetic field has a shielding effect to protect Mars from solar wind interaction, and this effect is the strongest for perihelion conditions, with the crustal field facing the Sun. Furthermore, the fraction of cold escaping heavy ionospheric molecular ions [( 2+ and/or 2+)/Total] are inversely proportional to the fraction of the escaping (ionospheric and corona) atomic ion [O+/Total], whereas 2+ and 2+ ion escape fractions show a positive linear correlation since both ion species are ionospheric ions that follow the same escaping path.