Comprehensive comparison of two global multi-species MHD models of Mars

Understanding the interaction between Mars and the solar wind is crucial
for comprehending the atmospheric evolution and climate change on Mars. To
gain a comprehensive understanding of the Martian plasma environment,
global numerical simulations are essential in addition to spacecraft
observations. However, there are still discrepancies among different
simulation models. This study investigates how these discrepancies stem
from the considered physical processes and numerical implementations. We
compare two global multispecies MHD models: the “Sun model” based on the
BATS-R-US code and the “Sakata model” based on a newly developed
multifluid model MAESTRO. By employing the same typical upstream
conditions and the same neutral atmosphere for current Mars, along with
similar numerical implementations such as inner boundary conditions, we
obtain simulation results that exhibit unprecedented agreement between the
two models. The dayside results are nearly identical, especially along the
subsolar line, indicating the reliability of MHD models to predict dayside
interaction under given upstream conditions and ionosphere assumptions.
The escape rates of planetary ions are also in good agreement. However,
discrepancies remain in the terminator and nightside regions. Detailed
numerical implementations, including inner boundary conditions, magnetic
field divergence control methods, and radial resolutions, are shown to
influence certain aspects of the results greatly, such as magnetotail
configuration and ion diffusion.