Numerical Simulation Study Of Martian Subsurface Water Ice Effects On Dust Storm And Atmospheric Radiative Dynamic Process

Mars is the most earth-like planet in the solar system,and Martian environment has long been a hot topic in planetary science.The spatial and temporal distribution characteristics of Martian subsurface water ice and its effect on dust storms and atmospheric radiative dynamic process are important parts of the Martian surface environment system,researches on them are of great significance for understanding the current Martian atmosphere evolution and carrying out future Mars exploration missions.However,the understanding of atmospheric radiative dynamic process,especially the effects of Martian subsurface water ice on it,are still incomplete at present,and the effects of subsurface water ice on dust storms evolution and its further influence on atmospheric radiative dynamic process has not been studied.Therefore,this paper focuses on these issues.This paper first investigated the evolution process of global dust storm and atmospheric radiative dynamic process in the Martian year(MY)34 by using the probe data and the simulation results of Mars general circulation model LMD-MGCM without subsurface water ice,combined with diagnostic methods such as super-rotation index,zonal mean mass stream function and potential vorticity.Then,based on the latest subsurface water ice distribution probe results,a subsurface water ice sublimation module was constructed in LMD-MGCM,and a subsurface water ice sublimation scheme was designed to study the effect of subsurface water ice sublimation on the global dust storm and atmospheric radiative dynamic process.The main conclusions were as follows:(1)Simulation results without subsurface water ice.MY34 global dust storm is divided into the following three phases: pre-occurrence phase(Ls=150°-180°),growth phase(Ls=185°-210°)and decay phase(Ls=210°-240°).The global dust storm then expands eastward.The vertical distribution of dust during the growth and decay phase shows a diurnal variation of 5-10 km higher in the daytime than in the nighttime.Both the probe data and simulation results show that dust can significantly heat the Martian atmosphere,but the simulated dust vertical distribution and atmospheric temperature at high latitudes in the southern hemisphere are 5 km and 10 K lower than those probed,respectively.The atmospheric circulations driven by dust thermal action change the atmospheric dynamic structure significantly.The specific conclusions are as follows:With the occurrence of the global dust storm,the equatorial super-rotation westerly jet and mean meridional circulation are significantly strengthened,which also play a key role in the zonal and vertical transport of dust.Meanwhile,the diurnal variation of mean meridional circulation plays a good role in explaining the diurnal variation of dust vertical distribution.In other words,there is a interaction between dust and equatorial super-rotation westerly jet and mean meridional circulation.With the occurrence of the global dust storm,the zonal component of the horizontal motion in the southern hemisphere high latitudes weakens and the meridional component strengthens,which weaken the Antarctic polar vortex.Moreover,the Antarctic polar vortex also shows diurnal variation characteristics,and the Antarctic polar vortex is always centered around local time 06:00.The mean meridional circulation plays a key role in the horizontal transport of water vapor from the southern polar region to middle and low latitudes and the vertical transport from low altitude to high altitude.(2)Simulation results with subsurface water ice.The inclusion of subsurface water ice in LMD-MGCM improves the significant difference between dust vertical distribution and atmospheric temperature at high latitudes in the southern hemisphere simulated by the model without subsurface water ice and probe data.In particular,dust vertical distribution and atmospheric temperature increased by 1-2 km and 2-6 K,respectively.The subsurface water ice sublimation mainly concentrates in the middle latitudes of the southern hemisphere,and water vapor is transported to the low latitudes and upper altitude of the southern hemisphere under the action of the mean meridional circulation,which makes the water vapor content increase significantly in the middle and low latitudes of the southern hemisphere,and the increase characteristics of water vapor are more significant in the daytime than in the nighttime.After water vapor is transported to the upper altitude,it cools and condenses on the surface of dust particles,leading to a large increase of water ice particles in the upper altitude and a large increase of water ice clouds.The increasing characteristics of water ice clouds are more significant in the nighttime than in the daytime.The increased water ice clouds change the temperature of the Martian atmosphere through radiation,strengthen the mean meridional circulation,and strengthen the vertical transport of dust,which makes the dust show the redistribution characteristics of increasing in the high altitude and decreasing in the low altitude,and this feature is more obvious in the nighttime than in the daytime.Through the above processes,a radiative dynamic process that starts with the radiation effect of water ice clouds is formed.