ENSO对我国东部极端降水的季节影响

利用百分位法定义极端降水阈值，对我国东部地区极端降水在不同季节对ENSO的响应特征加以研究，并以湿位涡作为切入点从大气性质角度出发分析其可能成因。结果表明：暖、冷年当年夏季极端降水对比显著区域主要在华北地区东部，分别表现为负距平区和正距平区；在暖年次年夏季和春季分布形有相似之处，北方多极端降水，南方分布形势较为复杂，江南地区也有极端降水大值区；次年秋季，与春夏季相比，极端降水大值区主要分布在北方；到了次年冬季，整个东部地区以极端降水负距平为主，冷年次年四季极端降水基本呈相反的分布形势；对应的湿位涡场能很好的反映北方地区尤其是华北地区的大气稳定性，而在低纬度地区还不能作为很好预测极端降水分布情况的依据

IMPACT OF ENSO ON THE SEASONAL EXTREME RAINFALL OVER EASTERN CHINA

ENSO is one of the most significant signal to the mutual coupling between the atmosphere and the sea.In this paper the response characteristics of the extreme rainfall over eastern China(the areas to the east of 100°E) in different seasons to the ENSO were studied by taking the use of the percentile method to define the extreme precipitation，and the possible reasons in the air properties were also analyzed by the use of moist potential vorticity(MPV) because of its own characteristics.The results showed that the threshold of the extreme rain reached the heavy rain standard in most areas in the summer since it was a rainy season itself and achieved only moderate rain in the winter.The frequency of the seasonal extreme precipitation showed its special distribution characteristics that in the spring the extreme rain mostly occured in the south area and in the summer the areas along the coast and in the southwest showed more extreme rain.While in the autumn it was the most area of the westsouth which had more extreme rain,and the northeast of the Neimeng province occured less in each season.When it came to the ENSO,it had another pattern.The extreme rainfall differed significantly over the east area of the Northern China in the warm and cold years，respectively the negatively anomaly filed and the positive anomaly field．In the spring and summer of the following year of Einino，it had nearly the same distribution that the north exsited more and the south exsited a complex distribution that there was a great value over the south area of the Yangtze River valley.In the autumn of the following year，constrasting to the spring and the summer，the big value shifted apparently and it was main over the northern region；and in the winter of the following year of Einino，it mainly had less．However，it nearly presented an adverse distribution pattern in the following year of Lanina.According to the study above we could conclude that in the summer of the following year,the extreme precipitation distribution differed from spatial distribution of the precipitation.In addition,the spring and summer of the following year of the cold year had a higher reliability,while in the autumn and winter it was the following year of the warm year which was more credible.The corresponding MPV could well reflect the atmospheric stability of the north area，especially over the Northern China,that is to say the MPV showed a positive anomaly field over the Northern China in the summer of the warm year and a negative anomaly field in the summer of the cold year.However,because of the many factors affecting the extreme precipitation,only taking the advantage of the changes of the atmospheric nature can not well be the fine basis of the extreme precipitation forcast in the low latitude region