Eurasian Subarctic Summer Climate in Response to Anomalous Snow Cover

The summer climate in northern Eurasia is examined as a function of anomalous snow cover and processes associated with land-atmosphere coupling, based on a composite analysis using observational and reanalysis data. The analysis confirms that the snow-hydrological effect, which is enhanced soil moisture persisting later into the summer and contributing to cooling and precipitation recycling, is active in eastern Siberia and contributes to the formation of the subpolar jet through the thermal wind relationship in early snowmelt years. Strong anticyclonic differences (early - late snowmelt years) with a baroclinic structure form over eastern Siberia as a result of surface heating through the snow-hydrological effect in early snowmelt years. Surface heating contributes to the development of thermally generated stationary Rossby waves that propagate eastward to eastern Siberia. Rossby wave activity is maintained into early autumn, together with cyclonic differences over far eastern Siberia, in conjunction with the early appearance of snow cover in this region. The anticyclonic differences over eastern Siberia act like a blocking anticyclone, thereby strengthening upstream storm track activity. Furthermore, it is possible that surface anticyclonic differences over the Arctic contribute to year-to-year variability of summer Arctic sea ice concentration along the Siberian coast. The results suggest that variations in northern Eurasian snow cover and associated land-atmosphere coupling processes have important implications for the predictability of Eurasian subarctic summer climate.