The comparison of the simulated response to the regional snow mass anomalies over Tibet, Eastern Europe, and Siberia

The atmospheric response to the regional snow mass anomalies in early spring over Tibet, Eastern Europe, and Siberia is compared by general circulation model ensemble experiments. The positive snow mass anomalies over Tibet produce the largest cooling anomalies in the atmosphere from spring to early summer. Almost no significant forcing anomalies are systematically formed by the snow mass anomalies over Eastern Europe and Siberia. The model experiments show that the cooling source over Tibet works significantly to delay the seasonal transition from spring to summer in the Northern Hemisphere. It is confirmed by the simulated weak Asian monsoon. a weak lower tropospheric monsoon jet in South Asia, a weak large-scale divergence center at the upper troposphere in Southeast Asia. negative lower-layer geopotential height anomalies in the North Pacific and the North Atlantic, and the weak Walker circulation in the equatorial Pacific are simulated. The above noticeable response of the atmosphere to the snow mass anomalies over Tibet is associated with the following characteristics of Tibet as compared with Eastern Europe and Siberia; (1) The small snow melt speed over Tibet, probably due to its high elevation, maintains the early spring additional snow mass until almost the end of the climatic snow-melt season. (2) The snow albedo is effective because of large solar incidence and relatively small cloudiness over Tibet. (3) The existence of the anomalous snow cover works to cut the upward sensible heat flux rather than the evaporation over Tibet because of its dry ground condition. (4) The dry ground over Tibet makes it possible that all the anomalous snow-melt water is not drained as runoff, but a part of it is stored in the ground. (5) As pointed out by many researchers, the Tibetan Plateau plays an important role in the Establishment of the Asian monsoon. The above conditions (1)-(5) for the effective snow mass anomalies are found in the model Tibet, but these conditions would be satisfied by the real regions where the snow mass anomalies affect the atmosphere efficiently. The extended atmospheric responses are found in May for the East European case and in August for the Siberian case. These are accompanied by significant ground condition anomalies in northern Eurasia. Those ground condition anomalies are not directly related to the successive ground condition anomalies followed by the anomalous snow mass melt, and seem to be created after the water and heat of the initial snow mass anomalies are supplied into the atmosphere.