Objective classification of weather types for the Eastern Siberia over the 1970–2020 period using the Jenkinson and Collison method

Abstract

A daily catalogue of weather types based on the Jenkinson and Collison (JC) objective approach has been developed for the Eastern Siberia region of Russia (47.5°–67.5° N, 102.5°–132.5° E) during the period 1970–2020. The mean sea level pressure (MSLP) dataset from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis was used for the classification. A statistical analysis of the annual, seasonal and monthly distribution of 27 weather types has been accomplished. For the entire period, the most frequent weather types were found to be anticyclonic (A, 23.5%), followed by cyclonic (C, 11.5%), unclassified (U, 9.1%) and the pure advective types N (6.9%), NE (6.0%) and W (5.4%). The advective atmospheric patterns are predominated by northerly and westerly components, which tend to weaken in summer and strengthen in the winter and transitional seasons. The westerlies dominate in the cold half of the year (October–March), while the easterlies are prevailing in the warm season (April–September). The long-term trends in frequencies of the atmospheric circulation patterns over the study period have been analysed. There are statistically significant decreasing trends of anticyclonic weather types, while types with northerly and westerly components show increasing trends. The relationships between the atmospheric circulation patterns and surface precipitation were ascertained from 87 meteorological stations. Anticyclonic weather types are consistent with dry weather conditions in all seasons, while cyclonic and advective types with easterly component are correlated with wet weather conditions. The seasonal reversal of zonal airflow across the study area (the westerly flow in winter and the easterly in summer), accompanied by the wetter weather conditions for the easterly circulation patterns, suggests the influence of the East Asian monsoon. Regional climate changes of recent decades, such as accelerated glacier shrinkage in the 1990s, increasing the number of droughts, and rainfall variability are in good agreement with the revealed atmospheric circulation patterns.