  We study roles of the thermosphere and exosphere on the Martian ionospheric
structure and ion escape rates in the process of the solar wind-Mars
interaction. We employ a four-species multifluid MHD (MF-MHD) model to simulate
the Martian ionosphere and magnetosphere. The $cold$ thermosphere background is
taken from the Mars Global Ionosphere Thermosphere Model (M-GITM) and the $hot$
oxygen exosphere is adopted from the Mars exosphere Monte Carlo model -
Adaptive Mesh Particle Simulator (AMPS). A total of four cases with the
combination of 1D (globally averaged) and 3D thermospheres and exospheres are
studied.
  The ion escape rates calculated by adopting 1D and 3D atmospheres are
similar; however, the latter are required to adequately reproduce MAVEN
ionospheric observations. In addition, our simulations show that the 3D hot
oxygen corona plays an important role in preventing planetary molecular ions
(O$_2^+$ and CO$_2^+$) escaping from Mars, mainly resulting from the mass
loading of the high-altitude exospheric O$^+$ ions. The $cold$ thermospheric
oxygen atom, however, is demonstrated to be the primary neutral source for
O$^+$ ion escape during the relatively weak solar cycle 24.

Earth and Planetary Astrophysics;Space Physics