Cold Waves in European Russia: Structure, Circulation Conditions, and Changes in Seasonal Statistics

Abstract

The statistics, structure, and variability of large-scale cold waves in various latitudinal zones of European Russia (ER) in the winter and summer seasons are considered. The largest number of waves is observed in winter in the south of ER and in summer in the north. The contribution to the total seasonal duration of the longest waves (more than 12 days) is observed in winter in the north (>40%); in summer, waves of such duration are not observed in the center and south of ER. Winter cold waves in all zones are characterized by areas of negative temperature anomaly, covering almost the entire territory of Russia, with centers in the corresponding zone of the ER and extending eastward up to 140° E. Summer waves have a three-field structure with centers of cold over ER and the west of Western Siberia and over Yakutia, and a positive anomaly in the eastern part of Western Siberia and western Central Siberia. Circulation structures in the troposphere accompanying the cold waves and their role in the formation of temperature anomalies are discussed. In winter, the H500 geopotential fields during waves in the center and south of ER are characterized by a powerful ridge over the north of ER and the Scandinavian Peninsula (which corresponds to the Scandinavian atmospheric circulation mode) and a trough in the south of ER and Western Siberia. Cold waves in the northern zone occur with a crest in the Atlantic north and a trough in the south (the North Atlantic Oscillation (NAO) negative phase) and a trough in the north of ER. Summer cold waves in all zones are accompanied by a cutoff cyclone centered in the corresponding zone (slightly to the north for waves in ER south); a negative geopotential anomaly over ER corresponds to the negative phase of East Atlantic–West Russia (EAWR) mode. The seasonal wave duration series during the 20th to the first two decades of the 21st centuries exhibits pronounced long-term variability with time scales of about a decade and several decades. In summer, there has been a downward trend in the seasonal duration of cold waves in all ER zones since the mid-1970s, especially significant (in terms of contribution to overall variability) in the south. In winter, a downward (insignificant) trend is observed only for waves in the north. In the south and especially in the center, the total duration of cold waves increases from the 1990s to the end of 2000s. The connection between this behavior of the total duration of winter waves and changes in the Atlantic–European sector leading circulation modes is discussed.