Intraseasonal Snow Cover Variations Over Western Siberia and Associated Atmospheric Processes

摘要

The present study documents intraseasonal snow cover variations over western Eurasia and associated atmospheric processes using the latest Moderate Resolution Imaging Spectroradiometer/Terra daily snow cover product and National Centers for Environmental Prediction/National Center for Atmospheric Research atmospheric reanalysis. It is found that 9- to 30-day variation dominates total intraseasonal snow cover variations over western Siberia. Composite analysis based on 69 positive snow events over western Siberia reveals that atmospheric circulation anomalies control the 9- to 30-day snow variation over western Siberia. A zonal wave train associated with the North Atlantic Oscillation leads to the development of an anomalous cyclone over western Siberia. The associated anomalous ascending motion, anomalous water vapor convergence, and water vapor increase in the atmosphere provide a favorable condition for snowfall. The snowfall starts when anomalous ascending motion reaches the strongest. The maximum snow cover appears about 1 day after the peak of anomalous descending motion and water vapor flux divergence. The surface air temperature tends to vary out of phase with snow cover over western Siberia. Surface air temperature anomalies over western Siberia are contributed by horizontal advection and diabatic heating. The adiabatic heating has a damping effect in surface air temperature variation.