Solar cycle variability of Mars dayside exospheric temperatures: Model evaluation of underlying thermal balances

Abstract

The response of the Mars dayside exospheric temperatures to short and long term solar flux changes was recently established. Characterization of the relative importance of various thermospheric heating and cooling mechanisms for maintaining these Mars exospheric temperatures requires the systematic application of modern global dynamical models that capture both lower and upper atmosphere thermal and dynamical processes. Coupled Mars General Circulation Model (MGCM) plus Mars Thermospheric General Circulation Model (MTGCM) simulations are utilized for this study, closely matching conditions during Mars Global Surveyor drag measurements. Simulations confirm the major balance of EUV heating and thermal heat conduction at dayside exospheric altitudes. However, the influence of variable Martian global winds is significant and must be carefully considered when investigating the global regulation of Mars exospheric temperatures over the solar cycle and Martian seasons. Finally, the present MGCM-MTGCM heating and cooling processes suggests that an EUV-UV heating efficiency of 19% yields net heating in accord with MGS exospheric temperatures. Copyright 2009 by the American Geophysical Union.