A study of the impacts of the eastward propagation of convective cloud systems over the Tibetan Plateau on the rainfall of the YangtzeHuai River basin.

Based on the TBB (temperature of black body) data from the GOES-9(2003) and FY2C(2007), the station observed data and the NCEP reanalysis data with the resolution of 1°×1° (four times a day), the impacts of the eastward propagation of convective cloud systems over the Tibetan Plateau on the rainfall of downstream areas during the Meiyu periods of 2003 and 2007 are analyzed in the present paper. The results show that, there mainly are 4 kinds of influencing patterns: (1) convergence centers over the Tibetan Plateau with convective systems move eastward and influence the rainfall of downstream areas in which the convective systems could last for a long time and influence large areas; (2) convective systems over the Tibetan plateau move eastwards out of the plateau and trigger a quasistationary southwest vortex in the Sichuan Basin in which the southwest vortex can last for a long time, and produce a series of heavy rainfalls in Sichuan and Chongqing, which sometimes cause severe floods there; if there is strong southwest winds to the east of the southwest vortex, positive kinetic energy transportation to the Meiyu zone is able to occur, which would enhance the convective activities and rainfall there; (3) convective systems over the Tibetan Plateau move eastwards and cause the formation of the southwest vortex moved along the Meiyu front with the eastward propagation of a small leading trough to the north; Under this condition, the southwest vortex will induce a series of convective systems and heavy rainfalls along Meiyu front, which always cause severe floods in the Yangtze River valley, and, as a result, in this pattern, the convective systems influence downstream areas most intensively; and (4) convective systems over the Tibetan Plateau move eastward out of the plateau and influence downstream areas directly in which the convective systems decay quickly and only influence downstream areas slightly (the influencing area is smallest, and the influencing time is shortest). The results of background circulation analysis show that, when the high jet at 200 hPa is located equatorward and at the same time the influencing trough (at 500 hPa) over the east part of the Tibetan Plateau moves eastward, the convective systems over the plateau are easy to move out.