Regional mean daily precipitation extremes over Central China during boreal summer and its relation with the anomalous circulation patterns

By using in situ precipitation records at the 239 stations in Central China (the Huazhong region) including Henan, Hubei and Hunan Province, and the NCEP/NCAR reanalysis data, the anomalous circulation patterns for the regional mean daily precipitation extreme (DPE) events over the Huazhong region in June, July and August of the boreal summer during the period from 1961 to 2010 were investigated. The results demonstrate that the threshold of the precipitation amount of the DPE events is 23.585 mm/d on the 99th percentile. The DPE events tend to occur more frequently from late June to mid-July, especially after the mid-1980s. The circulation anomalies of DPE events show a baroclinic structure throughout the troposphere. The water vapor is transported from the periphery of an anomalous anticyclone in the Bay of Bengal and the South China Sea northward into Central China. The wave activity fluxes on the northeastern side of the Tibetan Plateau converge around the Huazhong region, which is favorable to generating and maintaining of the wave perturbation in this region. The DPE events are also related to the heat gradient caused by the local net heating of air over the region and the net cooling of air in the surrounding areas. All of these suggest that the regional summer DPE events in Central China vary significantly on both interannual and interdecadal time scales. Also, the occurrences of the DPE events are closely associated with the anomalous cyclonic circulation, topographic forcing of the northeastern side of the Tibetan Plateau and the anomalous gradient of diabatic heating between Central China and the surrounding areas.