Precipitation And Circulation Patterns Of Daily Precipitation Extremes Over Central China During Boreal Summer

Investigated are the variations of regional mean daily precipitation extreme (RMDPE) events and the comparison between other level precipitation events in central China and the associated circulation anomalies for June, July and August in1961-2010by use of in situ daily precipitation data from239state-level stations distributed over the Provinces of Henan, Hubei and Hunan and NCEP/NCAR reanalysis datasets. Associated circulations3days before the DPE events are also brought into discussion. In addition, statistical analysis of the DPE events and its frequency of different stations are calculated, results are as follows:(1) The DPE events are significantly increasing in number from the mid-1980s on, with its frequent happening from late June to mid-July.(2) The DPE events are under the control of a baroclinically-structured anomalous circulation throughout the troposphere. The vapor in southern central China comes in a stepping way from the outer-region of an abnormal anticyclone over the Bay of Bengal and the South China Sea. The wave activity fluxes from the northeastern Tibetan Plateau converge into central China, in favor of the genesis and maintenance of wave disturbances over the region and besides, the DPE events occur in relation to the heating gradient formed by net heating in the target region and the large-scale net cooling of its ambient areas.(3) Results show that the DPE events happened in central China experience distinct interannual and interdecadal variations. The precipitation levels reduced with weak geopotential height, zonal wind, divergence intensity and a eastward precipitation center, the water vapor field and heat field are mostly the same, except the intensity falls down, the diabatic heating gradient in central China and its surroundings has a quick descent. There is significant difference of wave propagation perturbation energy and accumulation between different levels, but all influenced by the northeastern Tibetan Plateau.(4) There is going to be an enhancement to the circulation and baroclinicity from the lower troposphere to upper troposphere when the DPE event is about to happen. In the vertical wind field, the disturbance in the northwest Plateau develops to the east; there is a strong upward movement in central China at the same day the DPE events happen, and in its surrounding areas the movement turns from upward into downward. Warm and cold air masses converge in central China precipitation area and produce strong temperature gradient, which leads to the occurrence and maintaining of strong precipitation. In central China the accumulation of wave energy is mainly from the lateral dispersion of precipitation area from the northeast Plateau, and presents an obvious wave train structure at200hPa.(5) The distributions of the DPE events have distinct differences from one month to another. With rain belt moves northward from June to July, and achieves the low point in August. There is an obviously rising trend of precipitation and frequency of the DPE events in summer, but it varies month by month, it rises in June and July, and merely changes in August.The results show that such DPE events experience distinct interannual and interdecadal variations and every month has its own characteristics. The DPE events are bound up with the anomalies of cyclonic circulation in the study region, topographic forcing in the northeast Plateau and the anomalies of the diabatic heating gradient between central China and its surroundings.