The Impact Of Ground Frozen Thawing And Snow Melting On General Circulations On Tibetan Plateau

As one vast area with high elevation, the diabetic heating of Tibetan Plateau (TP) plays an important role in the Asian weather and climate system. Because of special geographical location and topography, TP has the largest frozen soil distribution in the middle altitude zone. The change of snow and frozen soil in the land surface processes on TP will inevitably affect regional thermal status, general circulations, and climate. Soil data from several observation stations on TP, ERA-interim dataset, cloud and precipitation data of satellites are analyzed in this work. First, the variations of water and thermal property of land surface processes and their relationship with cloud and radiation are analyzed after defining the time of ground frozen thawing and snow melting process (FTSM) on TP. Second, based on the characteristics of frequency oscillations of land and air, the variations of frequency oscillations and relationship with diabetic heating on TP in general circulations during FTSM are studied. Finally, the effect of change of ground surface’ albedo during FTSM on Eastern Asian climate and general circulations are investigated through the climate model simulation. The major contents and results as follows:(1) The time of FTSM for whole TP occurs at March to April in every year. The period time of FTSM in central TP is shorter than Eastern and Western TP. With the increasing of soil temperature, soil moisture increased significant at the late stage of FTSM, which happened on Eastern TP earlier than Western TP and much earlier than Central TP.(2) The change of surface radiation occurs earlier than soil temperature/moisture on Eastern TP. The net surface thermal flux changes from absorbing heat to releasing heat in the late FTSM on Eastern TP. The mainly thermal flux also changes from sensible heat to latent heat during FTSM on Eastern TP. For the sensible heat flux, it changes first at Southeastern TP, and then occurs on whole TP. The clouds on TP during FTSM changed little, which is beneficial for the increased solar radiation on ground.(3) Power spectrum estimations of relative vorticity on 500 and 200 hPa pressure field shows that it exists quasi-biweekly oscillation period (10-20 days) during FTSM, which also exists for OLR (Outgoing Longwave Radiation). The vertical structure of this oscillation changes between barotropic and baroclinic structure over time.(4) There is a significant relationship zone between this quasi-biweekly oscillation for the diabetic heating and relative vorticity on 200 hPa pressure field during FTSM, and this zone move southward. This shows the oscillation happened at regions outside TP though motions of atmospheric waves.(5) The numerical simulation results show that:the decreased surface albedo on TP during FTSM increased surface temperature soon. This change has a relationship with the surface temperature higher at Yangtze River Basin during April to May, surface temperature lower at Northeast China during May to August, and geopotential height on 500 hPa pressure field higher on Eastern Asian during March to August. This means that the FTSM on TP has a relationship with the abnormal for temperature, precipitation and general circulations on Eastern Asia.