Constraints on Atmospheric Dust Properties in Radiative Transfer Models for Mars

Dust in the Martian atmosphere remains one of the most important, and poorly understood factors for atmospheric heating and climatic cycles. The upper atmosphere, in particular, is where ¨background¨ levels of dust may have an impact on the development and dissipation of major dust storms. There, the dust temperature is not as well coupled to that of the surrounding carbon dioxide gas. Previous radiative transfer approaches leave out the variation of dust temperature with particle size, and size distribution with altitude. The Thermal Emission Spectrometer (TES) and upcoming Mars Climate Sounder (MCS) have and will provide excellent data on the vertical structure of the atmosphere and dust distribution. In this work we investigate models that treat coupling between dust and gas for different particle distributions with altitude. These models have been used to investigate the effects of dust on the heating of the atmosphere, particularly the upper atmosphere where derivations of carbon dioxide temperature profiles are less accurate, and missions such as the proposed Sample Collection for Investigation of Mars (SCIM) have the potential to probe. Dust is already understood to play a role in heating all levels of the atmosphere during major dust storms when overall atmospheric temperatures are elevated. We use a slab model with Eddington factors and some scattering parameters, calculated with previously derived indices of refraction using Mie theory for spherical particles. We choose this approach to probe the sensitivity of models to dust temperature and altitude variation effects, without dealing with all of the complicating variables at once. The initial results of these models indicate that the variation of temperature in different sized populations of dust, as well as variation in that size distribution in the upper atmosphere can have an effect on the overall radiative balance and the accuracy of the physical properties derived from models thereof. An important application will be the derivation of better parameters for Mars General Circulation Models (MGCMs) dealing with the upper atmosphere.