[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.

[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.

[1] The magnetosphere contains a significant amount of ionospheric O + , particularly during geomagnetically active times. The presence of ionospheric plasma in the magnetosphere has a notable impact on magnetospheric composition and processes. We present a new multifluid MHD version of the Block-Adaptive-Tree Solar wind Roe-type Upwind Scheme model of the magnetosphere to track the fate and consequences of ionospheric outflow. The multifluid MHD equations are presented as are the novel techniques for overcoming the formidable challenges associated with solving them. Our new model is then applied to the May 4, 1998 and March 31, 2001 geomagnetic storms. The results are juxtaposed with traditional single-fluid MHD and multispecies MHD simulations from a previous study, thereby allowing us to assess the benefits of using a more complex model with additional physics. We find that our multifluid MHD model (with outflow) gives comparable results to the multispecies MHD model (with outflow), including a more strongly negative Dst, reduced CPCP, and a drastically improved magnetic field at geosynchronous orbit, as compared to single-fluid MHD with no outflow. Significant differences in composition and magnetic field are found between the multispecies and multifluid approach further away from the Earth. We further demonstrate the ability to explore pressure and bulk velocity differences between H + and O + , which is not possible when utilizing the other techniques considered.

We present a time‐dependent MHD study of the controlling effects of the Mars crustal field on atmospheric escape. We calculate globally integrated planetary ion loss rates under quiet solar conditions considering the continuous rotation of crustal anomalies with the planet. It is found that the rotating crustal field plays an important role in controlling atmospheric escape. Significant time variation of ∼20% and ∼50% is observed during the entire rotation period for O+ and for normalO2+ and CO2+, respectively. The control is exerted mainly through two processes. First, the crustal magnetic pressure over the subsolar regime controls solar wind penetration and mass loading and therefore the escaping planetary ion source. There is a strong negative correlation between the magnetic pressure and ion loss, with a time lag of <1 h for O+ and ∼2.5 h for normalO2+ and CO2+. Second, the crustal magnetic pressure near the terminator region controls the cross‐section area between the induced magnetospheric boundary and 100 km altitude at the terminator. The change in day‐night connection regulates the extent to which planetary ions created on the dayside can be ultimately carried away by the solar wind and escape Mars. There is a strong positive correlation between the cross‐section area and ion loss, with no significant time lag. As the planet rotates, the dayside process and the terminator process work together to control the total amount of escaping planetary ions. However, their relative importance changes with the local time of the strong crustal field region.