1998年7月长江流域特大洪水期间暴雨特征的分析研究

对１９９８年７月下旬发生于长江中下游的暴雨，即“二度梅”，进行了初步的分析研究，认为：（１）在这一时期由于副热带高压的向南撤退并稳定在偏南位置，为长江流域降水提供了重要的条件；（２）中纬度系统维持两脊一槽的形势有利于冷空气的南下，而夏季风在这一期间偏弱，前沿停留于长江流域，同时与中纬度的偏北气流形成一条沿长江流域东西走向的切变线；（３）在这条切变线附近不断有中尺度系统发生发展，其中一部分中尺度系统达到很强烈的程度，甚至引发了８８４ｍｍ／ｈ的强降水；（４）对流层上层，如２００ｈＰａ上的高压，其东侧的强烈的辐散区正好位于长江中下游地区，上下层系统的有利配合，对这次暴雨的发生十分有利。

Study of Heavy Rainfall in the Changjiang River during July 1998

In this paper, the heavy rainfall in the Changjiang River during July 1998 has been studied. The main conclusions have been made as follows: (1) Subtropical high associated with the rainband position, retreated southward and maintained in South China. The large scale systems were very favorable to the occurrence of heavy rainfall in the Changjiang River during July 1998. (2) Troughs in the middle latitude was located in North China and Mongolia and cold air came from the trough invaded southward to the Changjiang River. (3) Summer monsoon weakened in 1998, it advanced just to the Changjiang River rather than North China, and transported a very rich moisture and warm air to the Changjiang River area. (4) A shear line formed between cold air from North China and warm air from tropical ocean, and maintained along the Changjiang River. (5) Some severe mesoscale systems occurred and developed in the shear line in the middle reaches of the Changjiang River. It was the mesoscale systems that produced the severe heavy rainfall in the Changjiang River, in July 1998.