Climate memory of snow mass as soil moisture over central Eurasia

Abstract

The interseasonal carryover of the central Eurasian snow mass anomaly as a subsequent soil moisture anomaly is studied on the basis of observational data. Regional focus is placed on the semiarid region north of the Caspian-Aral Seas, included in central Eurasia, for which the snow cover exhibits a significant correlation with the Indian summer monsoon rainfall. In general, over this region the snow depth reaches a yearly maximum during late February to early March, while the soil moisture exhibits a maximum in early April due to snowmelt and attenuates to a minimum during midsummer. On the interannual basis, a larger (smaller) yearly maximum snow depth leads, through a later (earlier) snow disappearance, to a higher (lower) soil moisture. This carryover of the land-surface anomalies was observed in a limited region, represented by Ural'sk (51°15′N, 51°24′E), which has the following climatic and soil conditions: (1) The yearly maximum snow depth represents a major portion of the soil water upon snow disappearance. When this is not the case, the maximum snow-depth-soil-moisture correlation is weakened due to the input of meltwater that is produced prior to reaching maximum snow depth (during the snow-increasing phase) and/or input of rainfall during the cold season. (2) The yearly maximum soil moisture during snow disappearance is lower than the field capacity. When this is not so, snow mass anomalies exceeding the field capacity are not maintained, due to the loss of excessive meltwater as runoff. In addition, the potential effect of seasonally frozen soil on the carryover is addressed. Even at Ural'sk, the carried-over soil moisture anomaly has reduced amplitude during the relatively dry spring. These results suggest that the soil moisture anomaly may not have a direct effect on the Indian summer monsoon through land-surface-atmosphere interaction. Copyright 2001 by the American Geophysical Union.