Spring Snow-Disappearance Timing and Its Possible Influence on Temperature Fields over Central Eurasia

Abstract

An observational study of snow-cover/atmosphere interactions that occur over Eurasia during the spring snow-disappearance season was conducted. Snow-disappearance timing was determined using five-day averaged snow depth data for 1966 to 1990 in the former Soviet Union (FSU). The climatological snow disappeared in the FSU area during early March in the southwest, and later during early June in the northeast. An empirical orthogonal function (EOF) analysis was applied to interannual anomalies of the snow-disappearance timings. The first EOF is the continental mode with widespread loadings of the same sign, the second mode (EOF2) is characterized by a loading pattern with an east-west dipole structure. The regional focus is placed on central Eurasia in the western pole of the EOF2 loadings, since the spring snow-cover for this region is found to exhibit a significant correlation with the Indian summer monsoon. A composite analysis for the opposite phases of EOF2 shows that, regardless of the leading snow depth during the late winter, the enhanced (reduced) large-scale advection of southerly warm upper-air towards central Eurasia during March and April was most likely to cause the earlier (later) snow disappearance. During mid-April, surface air temperature anomalies are largest over a wide area of central Eurasia, which has high variability in snow-cover extent, and south of the area. These temperature anomalies are larger than those at the 500 hPa level, likely due to the effect of the snow-cover, whereas the temperature anomalies disappeared by early May. This suggests that the snow-cover anomalies over central Eurasia may not have a direct effect on the Indian summer monsoon through the land-surface/atmosphere interaction.