山西省主汛期极端降水变化特征

Variation Characteristics of the Extreme Precipitation Event during the Main Flood Period in Shanxi Province

利用NCAR/NCEP再分析日资料计算了影响山西省区域的季风强度指数,并以山西省1960～2005年逐日降水资料为基础,采用线性趋势分析、小波分析等数理统计方法,分析了46年来山西省主汛期极端降水的变化特征。结果表明:考虑到季风在山西建立和撤退的多年平均日期,山西省的主汛期定为7月上旬到8月中旬更为恰当;山西省大部分地区主汛期降水量均呈下降趋势,但日降水大于30mm和50mm降水量却有所增加,尤以中部地区增多为主;20世纪60年代以来全山西省主汛期小雨日数明显减少;进入21世纪后,山西省主汛期降水虽然在减少,但极端强降水的次数有所增加,主要表现在中部地区大于30mm、大于50mm降水的日数和强度均有增加或增强的趋势。在多暴雨年份,500hPa位势高度异常场上在乌拉尔山附近地区易产生稳定的、强大的高压形势或阻塞形势,贝加尔湖至巴尔咯什湖一带有强低压槽,西太平洋副热带高压加强且北抬西伸,山西处于强低压槽的东南侧与副高西北侧的交汇带,且850hPa风场异常显示华北地区被一致的偏南气流控制,且与蒙古异常气旋南部的异常西风相遇,极有利于山西产生极端强降水。

By using NCAR/NCEP reanalysis daily data,the monsoon intensity index affecting Shanxi Province is calculated. Based on daily precipitation data of the stations in Shanxi Province for 1960-2005,the characteristics of the extreme precipitation in Shanxi main flood period for recent 46 years are studied by using linear trend analysis,wavelet analysis,and composite analysis. The results show that the dates of the main flood period in Shanxi Province should be from the first ten days in July to the second ten days in August,due to the climatological average onset and retreat of the summer monsoon in Shanxi Province. The rainfall in the main flood period over the most areas in Shanxi Province has a declining trend,but the rainfalls more than 30 mm and 50 mm have increasing trends,especially in the middle areas of Shanxi. The number of sprinkle （less than 1 mm） days has declined remarkably since the 1960s. Although the rainfall in the main flood period has still reduced,the number of rainstorms has increased since 2000. That is the number and intensity of rainfall more than 30 mm and 50 mm over the middle areas of Shanxi Province have increasing trends. In the rich rainstorm years,Shanxi Province is located in the convergent belt of the southeast part of the strong anomalous low pressure and the northwest part of the subtropical high in the 500-hPa potential height difference field,and North China is controlled by the strong south wind anomalies in 850-hPa wind difference field,which encounter with the anomalous west flow in the south of anomalous Mongolian cyclone,that is in very favor of strong rainstorm in Shanxi Province.