Wave-Breaking Features of Blocking over Central Siberia and Its Impacts on the Precipitation Trend over Southeastern Lake Baikal

Abstract

Precipitation over southeastern Lake Baikal features a significant decreasing trend in July and August over 1979-2018 and is closely related to blocking occurrence over central Siberia (45°–70°N, 75°–115°E). This study investigates the formation and maintenance of anticyclonic and cyclonic wave-breaking (AWB and CWB) blocking events and their climate impacts on precipitation in the southeastern Lake Baikal area. Both AWB and CWB blocking events are characterized by a cold trough deepening from the sub-Arctic region and a ridge amplifying toward its north over central Siberia, as well as an evident Rossby wave train over midlatitude Eurasia. For AWB blocking events, the ridge and trough pair tilts clockwise and the wave train exhibits a zonal distribution. In contrast, ridge and trough pair associated with CWB blocking events leans anticlockwise with larger-scale, meridional, and more anisotropic signatures. Moreover, the incoming Rossby wave energy associated with CWB blocking events is more evident than for AWB blocking events. Therefore, CWB blocking events are more persistent. AWB blocking events produce more extensive and persistent precipitation over the southeastern Lake Baikal area than CWB blocking events, in which moderate above-normal rainfall is seen in the decaying periods of blockings. A significant decreasing trend is found in terms of AWB blocking occurrence over central Siberia, which may contribute to the downward trend of precipitation over southeastern Lake Baikal.