Study on Characteristics of Tropical Plumes Related to Cold Season Rainstorms in Southern China
Cold season rainstorm is not rare in China and sometimes its strength and induced disaster is greater than that of warm season. Statistics show that about 80% cold season rainstorm events in South China are related to tropical plumes (TP). Therefore, in this paper, seven year (2005-2011) FY 2 geostationary satellite data, TRMM adjusted merged infrared precipitation dataset (3B42), ECMWF Interim reanalysis data and conventional observations including surface and soundings are used to examine the characteristics and behavior of tropical plumes which are dealt with cold season rainstorms in South China. The analyses reveal that most of the tropical plumes related to the cold season rainstorms in South China are generated within 0°-10°N, 70°-140°E area. The topographical effect to TP caused by the Tibetan Plateau can not be ignored. According to the propagation characteristics, the tropical plumes before eruption exhibit westward propagating in longitude time (Hovmoller) space, with a preferred phase speed of 15-20 m·s-1, comparable to or faster than the synoptic baroclinic wave. Generally, tropical plumes which are related to heavy rainfall always move faster in the pre eruption stage and are significantly influenced by the dynamic forcing coming from the mid upper level of troposphere than those dealt with weak rainfall. The pattern of the tropical plumes after eruption in the longitude time space suggest that the convection part in the cloud moves slowly and concentrates at the south west end of plumes. The sub tropical upper level jets act only to make the cloud cover to expand eastward quickly. The above features may cause the heavy rainfall centralized only over some stations.