Role of snow/ice cover in the Himalayan air mass exchange between the surface and the Troposphere

Strong local atmospheric circulations in the Himalayas can induce strong mass and energy exchange processes between the surface and the troposphere. The Himalayas snow/ice cover can affect this exchange processes by adjusting the local circulation systems. In this study, we used the RAMS model to investigate the effects of snow/ice cover on this exchange processes by evaluating the air volume fluxes between the troposphere and the Rongbuk Valley, in the Middle Himalayas. Two experiments were performed for a sunny day case, and the snow/ice cover was included in the control simulation and excluded in the sensitivity run. Our results show that, the down-valley flow dominated local wind system could pump down large amount of air from the troposphere to valley, i.e., approximately 37 times the enclosed valley volume is ventilated from the troposphere to the valley in a day. Without snow/ice cover, the local wind system is dominated by up-valley flow in the daytime and down-valley flow at night. Air mass is transported upward from valley to the troposphere in the daytime, and downward into the valley at night. As a result, approximately 66% of the downward transportation is contributed by snow/ice cover. This study indicates that under the background of global warming, decreasing snow/ice cover will affect the local wind circulation, and in turn will have an effect on the air mass exchange processes between the surface and the troposphere in the Himalayas.