The UCL martian thermosphere and ionosphere global circulation model: Development and validation.

Simulations of the Martian upper atmosphere have been produced from a self consis tent three dimensional numerical model of the Martian thermosphere and ionosphere called MarTIM. This model has been developed at UCL to cover an altitude range of 60km - 250km+. A radiation scheme is included that allows the main sources of heat input, EUV/UV and IR absorption by CO2 and CO, to be calculated. MarTIM self consistently calculates the composition of three of the main gases, CO2, N2 and 0, which are mutually diffused. These are treated as the major gases in the model. The other species densities (the minor gases), CO, Ar, O2 and NO, are based on dif fusive equilibrium above the turbopause. The ionosphere is calculated from a simple photoionisation and charge exchange routine which yields a peak electron density of around 2 TO5cm-3 at 135km, for Ls=0, solar minimum conditions. The semi-diurnal (2,2) migrating tide has been simulated and the results are presented and discussed. Comparisons of the model output to the available measurements from Mars Global Surveyor and Mars Pathfinder demonstrate that the fundamental parameters are well modelled and point to opportunities for further development. The fixed lower bound ary in the basic MarTIM was altered by using output from the Mars Climate Database as the lower boundary. The effects of this change at higher, thermospheric altitudes, has been calculated and reveals a significant dependence on this lower atmosphere input