【摘要】 在夏季青藏高原上低层没有辐合带和对流系统活动时,在高原东坡下午有对流云发展。在有利的地形条件下,这类对流云团可发展成中-a 系统,东移进入梅雨锋云带。在长江中游复杂地形区域中-a 尺度对流云团只具有较复杂的中尺度对流组织和较复杂的消、长更替等过程。这类中尺度云团有时停滞,有时发生跳跃性迁移。当梅雨锋云带上对流降水逐渐活跃和加强时,在对流层下部有冷带和温度锋区出现,并且当有一个强的中-a 尺度暴雨云团发展起来之后,可以在梅雨锋上形成3～4个中-a 尺度暴雨云团。同时在梅雨锋南侧低层不稳定区的中-α尺度对流云团移入梅雨锋云带时,容易引起强的中-α尺度云团发展。更多还原

【Abstract】 During the periods when the summer low-level convergence zone and convective activity inthe Tibetan Plateau are interrupted,the daily variable plain-mountain thermal circulation on theeast slope of the Plateau causes the development of convectional systems in the slope region.Thisis one kind of the mechanism that results in generation of meso-α scale convective cloud clustersin Sichuan basin.When these meso-α scale convective cloud clusters entered the complex topo-graphic region in the middle reaches of Changjiang River,the more complicated meso-scale con-vective organization appeared and alternation of weakening and strengthening occurred.In macro-scopic view,sometimes they stagnated and sometimes leaped down stream.When the convectiveprecipitation in Meiyu front cloud zone is activated and strengthened gradually,a cold band andthe corresponding thermal front emerged in the lowest layer,and when a strong meso-α scalecloud cluster with heavy rain developed up,a wave train which is composed of three or four meso-α scale clusters with heavy rain formed in the middle and lower reaches of Changjiang Riverthrough a quick adjustment process.As some meso-α scale convective cloud clusters,which areinitiated in the low-level unstable region in the south side of Meiyu front,came into Meiyu zone,strong meso-α scale cloud cluster may developed up more easily。更多还原