Summertime land-atmosphere interactions in response to anomalous springtime snow cover in northern Eurasia

摘要

An atmospheric general circulation model (AGCM) is used to investigate the effects of springtime high-latitude snow cover on the summertime climate system in the form of land-atmosphere interactions in northern Eurasia. We performed light and heavy snow runs in which the initial snow mass in northern Eurasia was varied. Significant differences in model response between the light and heavy snow runs are evident in terms of not only land surface parameters but also summertime northern atmospheric circulation. Changes in the initial snow cover have a strong effect on the simulated surface air temperature. In western Siberia, the albedo of the snow cover makes a strong contribution to the difference in surface heating between the runs, because snow mass anomalies are still present over western Siberia in June. In eastern Siberia (the Lena Basin), where the snow disappears in June in both runs, the snow-hydrological effect is prominent throughout summer. The increased soil moisture in the heavy snow run causes increased evaporation, resulting in turn in surface cooling. The initial soil moisture content is dry in eastern Siberia and wet in western Siberia, resulting in contrasting responses between the two regions. In the light snow run, the subpolar jet is strengthened and maintained along the Arctic coast in early summer, and wave activity propagates eastward over northern Eurasia. Changes in the atmospheric circulation generate an east-west dipole structure of precipitation anomalies over northern Eurasia. These results suggest that variations in the springtime Eurasian snow mass result in changes in the summertime northern atmospheric circulation and hydrological cycle via land-atmosphere interactions.