位涡分析在新疆暴雨研究中的初步应用

新疆是全国有名的干旱、半干旱地区，年平均降水量约147mm，不到全国平均值的1/4，但暴雨造成的洪水却是新疆的主要灾害之一。随着新疆气候由“暖干”向“暖湿”型的转变，暴雨出现的频率可能会增加，暴雨带来的洪涝也有可能比以往更加严重，因此有必要加强对新疆暴雨天气的分析研究。本文根据位涡理论，选取2004年7月18日～20日的一次由中亚低涡造成的盛夏暴雨过程做个例分析，对位涡与新疆地区降水和暴雨的关系进行了初步研究。结果表明：对流层高层十位涡能较好地反映冷暖空气的活动及天气系统的演变特征，位涡场比温度场、高度场能更清楚地示踪冷空气，这为研究冷空气的活动，特别是冷空气在触发暴雨中的作用提供了新的思路；对流层低层湿位涡与降水的强弱有良好的对应关系，当包线陡立时，易导致倾斜涡度发展，出现降水：当湿位涡MPV〈0时，在θe线陡峭密集区内易出现暴雨。

Preliminary Application of Potential Vorticity Analysis in Researching Heavy Rain in Xinjiang

Xinjiang is a well-known arid and semiarid region in China,and the annual precipitation here is 147 mm less than one fourth of the average in China.However,the floods brought about by heavy rain are one kind of the main natural disasters in Xinjiang.With the climatic change from warming-drying pattern to warming-wetting pattern in Xinjiang,heavy rain may occur more frequently,and the floods brought about by heavy rain may become more serious,so it is necessary to strengthen the study on heavy rain in Xinjiang.Based on the vorticity theory,the relations between the PV(potential vorticity) and the precipitation or heavy rain occurring in Xinjiang are preliminarily studied in this paper based on analyzing a heavy rain case caused by Central-Asian vortex from July 18 to 20,2004.The results show that the dry PV in the upper troposphere can well reflect both the cold and warm air current motions and present the developing features of the weather system,and the PV can trace the cold air current more clearly than the temperature or height field,which provides a new idea for studying the motion of cold air current,especially its effect in triggering a heavy rain.The moist PV in the lower troposphere has good relations with the intensity of precipitation.It is favourable for causing a rain when the moist isentropes are very stiff,which can lead to the development of slantwise vorticity,and a heavy rain will probably occur in the stiff and dense section of moist isentropes when MPV<0.