Synoptic Pattern and Severe Weather Associated with the Wide Convection over Southeast China During the Summer Monsoon Period

Based on the Tropical Rainfall Measuring Mission (TRMM) precipitation radar observations, wide con-vection (WC) is defined as contiguous convective echoes over 40 dBZ, accompanied with a near surface rainfall area exceeding 1000 km2. In Southeast China, the maximal occurrence frequency of WC takes place over the flat land region in the central plain of East China during the summer monsoon period of 1998-2010. When WC occurs in this region, the 500-hPa atmospheric fields are categorized into three patterns by using an objective classification method, i.e., the deep-trough-control (DTr) pattern, the subtropical-high-maintenance (STH) pattern, and the typhoon-effect (Typh) pattern, which respectively accounts for 20.8%, 52.8%, and 26.4% of the total WC occurrences. The DTr pattern starts to emerge the earliest (16-31 May) and occurs the most often in the second half of June; the STH pattern has a significant occurrence peak in the first half of July; the Typh pattern occurs mostly in July and August. Nearly all WC occurrences in this region are associated with thunderstorms, due to large convective available potential energy and abundant moisture. Among the three synoptic patterns, the DTr pattern features the driest and coldest air in the region, leading to the least occurrences of short-duration heavy rainfall. Strong winds occur the most often under the DTr pattern, probably owing to the largest difference in air humidity between the mid and low troposphere. Hail at the surface is rare for all occurrences of WC, which is probably related to the humid environmental air under all weather patterns and the high ( 5 km) freezing level under the STH pattern.