Land-atmosphere coupling in response to anomalous snowmelt and its impact on subarctic summer climate

We examined land-atmosphere coupling in response to anomalous snowmelt and summer climate in northern Eurasia, based on a composite analysis defined by anomalous northern snowmelt using observational and reanalysis data. In the early snowmelt years, our observational analysis confirmed that the snow-hydrological effect, which depends on snow mass and is a coupling between evaporation and precipitation, is active in eastern Siberia and acts to form the subpolar jet through the thermal wind relationship, as reported in our model study (Matsumura et al. 2010). In late summer, tropospheric heating over eastern Siberia is caused by the ascent due to surface heating as a result of the snow-hydrological effect, forming strong anticyclonic anomalies with a baroclinic structure. Thus a stationary Rossby wave generates thermally through the surface heating and emanates eastward around eastern Siberia. The wave activity is also maintained in early fall, together with the cyclonic anomalies over far-eastern Siberia, where the timing of snow-appearance is early. The anticyclonic anomalies over eastern Siberia act like a blocking anticyclone, thereby strengthening the upstream storm-track activity. Furthermore, we examined the development of the anomalous surface anticyclone, which leads to a cool summer in northern Japan, using a regional climate model. Our results suggest that variations in northern Eurasian snowmelt have important implications for the predictability of subarctic summer climate through land-atmosphere coupling. Reference Matsumura, S., K. Yamazaki, and T. Tokioka, 2010: Summertime land-atmosphere interactions in response to anomalous springtime snow cover in northern Eurasia. J. Geophys. Res., in press.