Study of Diffusion Modes in the Vertical Structure of Martian Atmosphere

In the vertical structure of the Martian atmosphere two diffusion modes can be distinguished: turbulent and molecular. Turbulent diffusion dominates in the lower atmosphere, the homosphere, where molecules are uniformly mixed with each other. In the upper atmosphere, the heterosphere, molecular mixing with diffusive separation of individual gas components prevails. The boundary layer, where turbulent diffusion changes to a molecular that is individual for each component, is called homopause (located in a range of heights from 100 to 130 km). In modeling the vertical transport of particles the consideration of the coefficients of the mentioned diffusion regimes plays a significant role. Currently, there is no universal method for determining the coefficient of turbulent diffusion due to its complex nature, which combines various dynamic processes. For the most accurate estimation of the diffusion coefficients the vertical distribution of atmospheric density and temperature is necessary, especially in the homopause region, where both turbulent and molecular components need to be considered. This work presents an analysis of the vertical profiles of temperature and density measured by the Russian Atmospheric Chemistry Suite spectrometric complex on board the Trace Gas Orbiter orbital module of the ExoMars mission. Based on the ACS data, various approaches to determining diffusion coefficients are considered, including both parametric models and a method that takes into account the contribution of wave effects in the atmosphere. According to the results of the processed observations over 2.5 Martian years, seasonal and latitudinal variations of the homopause altitude have been revealed, as well as its dependence on atmospheric density and diffusion coefficients in this transition region.