Analysis of a Meso-β Scale Convective System during a Brief Torrential Rain Event in Northeast China

In order to construct a predictive scheme of short-term torrential rainfall events over NE China a case study is made of the development of a meso-beta-scale convective system (MCS) that produced exceptionally heavy rainfall there on August 10, 2006, together with meso-scale environment, by means of automatic station data, satellite imagery and conventional observations. As an event of 100-yr return character, the downpour occurring in the central-western portion of NE China produced the maximal 1-hr precipitation of 90.8 mm at Tailai, with 82 mm thereof in the latter half hour. IR satellite and high-resolution visible cloud maps are employed to investigate how the MCS evolved from a meso-gamma into a meso-alpha MCC (Meso Convective Complex). Analysis shows that associated with higher than 33 mm in 30 min at 6 city-and county-level regions, the MCS was separated into 2 phases. In the first phase, i.e., before the MCC formation, the MCS moved mainly eastward, merging finally into the MCC, and in the second phase, i.e., the MCC mature stage, the MCS were in the southwestern fringe of the MCC, with the strongest precipitation observed there. Inspection of even higher-resolution visible images yields that where the northern and western cumulus lines met, the MCS developed vigorously enough to produce downpour. Examination of the MCS intensification and precipitation happening indicates that 1) high temperature, high humidity and convectively unstable stratification existed over the rainbelt, in conjunction with significant increase in convective available potential energy and decline of lifted condensation level and free convective height, in favor of the torrential rains; 2) mergence of meso-beta scale cloud clusters allowed MCS to develop quickly for rainfall; 3) the northern and western cumulus lines corresponded to two convergence lines on the surface wind field and at their meeting point strong convergence resulted in sufficiently intensely growing meso-beta cloud clusters to produce rainfall. Analysis of MCS propagation southwestward in the MCC yields that the movement of the rainstorm-producing MCS was dependent on the shift direction and velocity of the convergence lines.