1998年夏季北半球斜压波活动与长江流域洪涝灾害分析

对流层上层的斜压波、高空槽对天气的变化有重要的影响。1998年夏季我国出现了大范围的天气异常，在长江流域发生了20世纪第二大的全流域性洪水，分析了1998年夏季北半球的西风急流、风暴轴、以及对流层上的斜压波活动与气候平均情况的异同，并揭示了1998年夏季北半球斜压波活动传播的主要区域、斜压波活动的持续性、斜压波向传播的速度以及斜压波传播时所具有的明显的下游效应。1998年夏季北半球的波包 次数共有11次，与夏季气候状况相比属于正常偏多，其中5月和8月的波包活动次数稍多。但更为明显的一个特点就是在7月中旬到8月上旬大西洋－欧洲的斜压波包活动比往年集中频繁，而且持续时间偏长， 为造成我国异常梅雨天气和长江流域洪涝灾害的乌拉尔阻塞高压的发展和维持提供了能量支持，同时为长江流域以及同期我国东北的大范围降雨提供了有利的水汽输送条件。最后分析了地面气旋生成与斜压波、高空槽之间的联系，指出在大多数向东部发展的高空槽的槽前，地面上有对应气旋地生成。

Baroclinic Waves of Northern Hemisphere and Yangtze River Flood in the Summer of 1998

Baroclinic waves in upper?troposphere, upper troughs and surface cyclones associated with wave packets are important systems for weather change and prediction. In the summer of 1998, there was large-scale weather anomaly in China and the whole Yangtze River basin suffered a severe flood event, which is only next to 1954 in the 20th century. In this paper, westerly jet, storm track and baroclinic wave packets of upper troposphere in the Northern Hemisphere at summer of 1980?1998 are analyzed by using NCEP/NCAR re_analysis data. The analysis has indieated that the main propagation areas of baroclinic waves, the coherence of baroclinic waves, the phase and group velocity of baroclinic waves and the downstream development of baroclinic wave packets in the summer of 1998. It is found that there are 11 wave packets activities which can be tracked in the Northern Hemisphere at summer of 1998; the number is almost normal comparing with climate status except that there are more wave packets during May and August of 1998. However, much more wave packets concentrate and propagate over the Atlantic and Europe areas from the mid of July to the mid of August in 1998 than most of other years. These baroclinic waves provide energy for the development and maintenance of Ural blocking, which is of vital importance for the heavy rainfall and great flood of Yangtze River in 1998. At the same time, convergences of southwest winds due to unusual perturbations in the upper troposphere offer good water vapour transportation condition for the wide spread precipitation of the Yangtze river basin and northeastern China. We also analyzed the connections between surface cyclogenesis, upper trough and baroclinic wave packets. At the fore of most cases of upper troughs developing eastwards, there are always surface cyclogenesis. Baroclinic wave activities have important impacts on the weather anomaly of 1998 summer.