Interannual Variation in Snowfall over Songhua River Basin and Its Relationship with West North Pacific Sea Surface Temperature Anomalies during Boreal Winter

Abstract

Based on the 103 stations precipitation over Songhua River Basin （SRB）， the reanalysis data of NCEP/NCAR， the sea surface temperature （SST） from NOAA， the interannual variation in snowfall over SRB and its relationship with west north Pacific SST anomalies （SSTA） during boreal winter for 1979 -2019 are investigated by using statistical analysis methods.The results show that the snowfall over SRB during winter is mainly characterized by its interannual variation （explains 83.3% of total variation）， and the first leading EOF mode of interannual snowfall anomalies of SRB during winter is dominated by a homogeneous structure （explains 55.3% of total variance） indicating significant covariability over the SRB.The atmospheric circulation associated with the interannual SRB winter snowfall suggests that the above-normal （below-normal） snowfall is induced by positive （negative） geopotential height anomalies over the region from Okhotsk to Aleutian island and negative （positive） geopotential height anomalies over the mid-low latitude to the south of Okhotsk Sea.Further analyses indicate that the dipole structure of SSTA over WNP during winter has a profound impact on the simultaneous interannual snowfall over SRB.The positive WNP SSTA dipole （positive and negative SSTA over Japanese Sea and east to the Philippines Islands， respectively） can induce positive geopotential height anomalies in the upper troposphere and anomalous anticyclone in the lower troposphere in the mid-high latitudes over WNP， as well as the negative geopotential height anomalies in the upper troposphere and anomalous cyclone in the lower troposphere in the mid-low latitudes.The region from north Pacific to the SRB is covered by anomalous southeasterly winds during winter under the influence of these anomalous atmospheric circulation.As a result， the moisture from the sea to the south of Aleutian and the sea to the east of China are transported to the SRB accompanied by anomalous convergent flow in situ， which are favorable for the increasing snowfall over SRB； and vice versa.

Keywords

• songhua river basin
• winter precipitation
• atmospheric circulation
• sea surface temperature anomalies