Differing mechanisms for the 2008 and 2016 wintertime cold events in southern China

摘要

Southern China was hit by a severe cold event during January 21-25, 2016, characteristic of a drastic and sudden temperature drop, with new records of low temperatures set in widespread areas. This cold event was dynamically linked to the activity of the Arctic oscillation (AO) whose evolution led the event by about 2 weeks. Different from this short lasting but intense cold event in 2016, another cold event in the 2008 winter lasted much longer and occurred in tandem with freezing precipitation. Their differences in the duration and precipitation are essentially determined by differing behaviours of blocking highs at mid-high latitudes, the India-Burma Trough and the western Pacific subtropical high. The rapid southward invasion of cold air masses during the 2016 event resulted from the rapid decay of the blocking high, which emanated wave energies downstream and likewise lost wave energies to the local mean flow. By contrast, during the 2008 cold event, continuous upstream wave energy dispersion recurrently stimulated disturbances in the blocking domain, which then extracted energies from the mean flow efficiently to survive markedly longer. Moreover, in the 2008 case, the deepening of the India-Burma Trough and the westward extension of the western Pacific subtropical high jointly enhanced the moisture transport, leading to the freezing rain. This favourable configuration for precipitation was absent in the 2016 case, dictating its dry nature accordingly.