Spring northward retreat of Eurasian snow cover relevant to seasonal and interannual variations of atmospheric circulation

An observational study is made of the seasonal and interannual variations of spring snow-disappearance over the Eurasian continent and the circulation mechanisms causing those variations. The spring northward retreat of the snow boundary over the East European Plain (EEP) between 30 and 60degreesE is faster (0.4degrees per day) than to the east of the Ural Mountain range (0.3degrees per day). These migrations of the snow boundary lag behind the appearance of the surface air temperature 0degreesC by about 1 to 5 pentads. The analyses of the atmospheric heat and moisture budgets showed that the seasonal intrusion of warm air associated with southwesterly winds is primarily responsible for the rapid snowmelt in March and April over the EEP. In addition, the adiabatic heating of descending air plays a secondary role in the snowmelt in mid-March. On an interannual time scale, horizontal warm advection also plays an essential role in the spring northward retreat of snow cover extent. The present study confirms the previous finding that the surface air temperature anomalies, produced during the seasonal snow-disappearance period, diminished in May, suggesting a weak dynamical linkage between the EEP snow cover and Asian summer monsoon. Copyright (C) 2003 Royal Meteorological Society.