Synoptic classification of atmospheric circulation over the south Eastern Siberia and its relationship with glacier dynamics

The energy balance of a glacial surface and its melting is strongly controlled by altering synoptic processes in the lower troposphere. Therefore, classification of the processes of atmospheric circulation over the glaciarized regions is very important for better understanding of long-term trends in glacier changes. The glaciers of the Kodar Ridge (south Eastern Siberia) have shrunk in area by about 60% since the mid-19th century, with the largest decline taking place at the end of the 20th century. We have compiled the daily catalog of the weather types (WTs) from 1970 to 2020 based on the Jenkinson and Collison objective classification applied for the area (47.5–67.5° N, 102.5–132.5° E) centered over the Kodar Ridge. The gridded sea level pressure (SLP) and isobaric 700 hPa data was obtained from the National Center for Environmental Prediction / National Center for Atmospheric Research (NCEP/NCAR) reanalysis. In total, 26 WTs were identified and the frequency of different synoptic types was statistically analyzed. The most frequent group of WTs is advective (40%), followed by anticyclonic (34%) and cyclonic (14%). The unclassified type totally accounts for 13%. We revealed the differences between the frequency of synoptic processes in seasonal cycle and at different atmospheric levels (SLP and 700 hPa). Cyclonic weather types usually prevail in summer, while anticyclonic ones in autumn and winter. At 700 hPa level, the frequency of anticyclonic WTs increases in summer, while the frequency of advective types increases in all seasons. Over the past 50 years, the frequency of anticyclonic types demonstrates decreasing trend, while that of cyclonic and advective weather types increased (SLP data). In the 1980s and early 1990s the frequency of cyclonic WTs decreased, which could lead to a decrease in cloud cover over the Kodar region and an increase in net radiation of glacier surfaces. This study was supported by the Russian Foundation for Basic Research (project No. 19-05-00668).