( 2 ) sxsp anomaly is closely related to the abnormity of 500hpa geopotential height field over the east of ural and yakutsk area , western ridge point and area of subtropical high , the cold air abnormity from north of china and the position of upper level westerly jet over east asia ( 2 )三峡库区夏季降水异常与大气环流异常密切相关：与500hpa乌拉尔山以东高度场异常、雅库茨克以东高度场异常、副热带高压面积及西伸脊点、北方冷空气异常、 200hpa东亚高空西风急流位置异常偏南(偏北)密切相关。
Monthly rainfall data from 1951 to 1995 for june , july and august in 13 meteorological stations of the north china were used for accounting z index and discussing serious flood and drought featureas in these months . serious flood mainly happened in july and august , and sevious drought mainly happened in august . there were more flood in 1950 ' s to 1960 ' s and more drought since 1970 ' s in the north china . meanwhile , the deeper trough which covered the regions from the ural mts . to the balkhash lake play an important role in serious rainstom in rainy season in the north china . there often happened serious flood ( drought ) when the northwester pacific subtropical high was by west and north ( east and south ) , and the sea surface temperature in the equatorial central and eastern pacific was mainly in dropping ( raising ) stage 利用华北平原地区的13个站点, 45年（ 1951 1995 )的降水资料,对夏季4个时段（ 6月、 7月、 8月、 6 8月）进行了z指数计算,确定了该地区各个时段的严重涝年和严重旱年.发现华北地区雨季的严重洪涝主要集中在7 , 8月,严重干旱则主要发生在8月,并可明显看出由50 60年代的多水期向70年代中期以后的少水期的转变,另外,乌拉尔山到巴尔喀什湖附近的低压槽加深和西北太平洋副热带高压的北抬,对华北地区雨季持续性暴雨的产生起着决定性的作用.严重洪涝年的夏季（ 6 8月） ,西北太平洋副热带高压偏西、偏北,赤道东太平洋海温多处于下降阶段;严重干旱年西北太平洋副高偏东、偏南,赤道东太平洋海温则处于上升阶段
