Contrasting Relationship between Wintertime Blocking Highs over Europe–Siberia and Temperature Anomalies in the Yangtze River Basin

Abstract

Based on the Japanese 55-year reanalysis dataset, this study identifies 92 Europe–Siberia blocking high events (ESBs) over the 60 winters (November–March) from 1958/59 to 2017/18. According to the influence on the surface air temperature at 2 m over the middle and lower reaches of the Yangtze River, the ESBs are classified into three types: cold, neutral, and warm. Although cold-type ESBs are dominant, the number of warm-type ESBs is not negligible. The present study mainly focuses on the differences between cold-type and warm-type ESBs. Both the cold-type ESBs and the warm-type ESBs are characterized by height anomalies with a northwest–southeast-tilting dipole pattern over the Eurasian continent in the mid- and upper troposphere. However, the tilting dipole pattern of the warm type is located to the northwest of its cold-type counterpart, which reflects differences in the propagation of Rossby wave packets. The Siberian high is stronger in cold-type ESBs than in warm-type ESBs. The induced advection of the climatological mean air temperature by the anomalous meridional wind velocity in the lower troposphere accounts for the largest portion of the observed tendency of the air temperature for both ESB types. In addition, diabatic heating tends to counteract the local cooling tendency of air temperature over the Yangtze River region for the cold-type ESBs. Finally, cold-type ESBs are generally characterized by air parcels originating in the region to the north and northeast of the Tibetan Plateau, while warm-type ESBs are characterized by diverse trajectories.