初夏东亚季风强度指数与陕西降水异常关系

East-Asian summer monsoon intensity indexes in early summer and their anomalous relationship with precipitation in Shaanxi Province

应用1979-2011年NCEP/NCAR再分析资料和陕西地面月降水资料,分析计算东亚初夏季风强度指数和陕西降水距平一致率,采用统计相关分析方法分析初夏东亚季风强度指数与陕西降水异常的统计关系,并采用合成分析方法讨论了初夏强(弱)东亚季风年陕西多雨(少雨)的大气环流特征。结果表明:初夏东亚季风偏强,陕西易多雨,且陕北、关中比较显著,而初夏东亚夏季风偏弱,陕西易少雨,偏少的程度陕北北部最明显;初夏东亚季风偏强时,欧亚中高纬度距平场自西向东呈"+-+"的波列分布,环流场中乌拉尔山长波脊偏强,贝加尔湖到巴尔喀什湖低槽偏深,西太平洋副热带高压偏强,相应的对流层低层青藏高原东侧为偏南距平风,而华北为弱偏东距平风,在西北地区东部形成了距平风的气旋性切变,有利于该区域初夏多雨;初夏东亚夏季风偏弱时,欧亚中高纬度距平场距平自西向东呈"-+-"的分布,中亚长波脊强盛,西太平洋副热带高压偏弱且位置偏东。陕西主要受中亚高脊前西北气流控制,陕西初夏多晴热天气,易少雨;但初夏东亚季风偏弱时,东亚中纬度盛行平直西风气流,西风锋区位于40°N附近,西太平洋副热带高压位置偏西偏南,青藏高原位势高度偏低,并多短波槽或低值系统活动,陕西初夏受西风带系统和高原东移的低气压系统影响,陕西大部易多雨。

By using the NCEP/NCAR reanalysis data and monthly precipitation data in Shaanxi Province from 1979 to 2011, the East-Asian summer monsoon intensity index and precipitation anomaly consistent rate were calculated, the relationships between the monsoon intensity indexes and precipitation were investigated using statistical correla- tion analysis method. The atmospheric circulation characteristics of Shannxi rainy year and drought year were dis- cussed with the strong （weak） East-Asian summer monsoon. The result showed that：the strong East-Asian summer monsoon meant more rain in Shaanxi, and Asian summer monsoon meant less rain, an plenty rainfall in North Shaanxi and Guanzhong, while the weak East- d significant less in the north of Northern Shaanxi. The more rain had the characteristics of a positive-negative-positive anomalous distribution from west to east in high latitudes in Europe and Asia, general circulation of the stronger ridge at Ural Mountain, deeper trough from Lake Baikal to the Balkhash, stronger west Pacific subtropical high, the south airflow prevailing the east side of Tibetan plateau, meanwhile the weak north airflow prevailing in North China. There was cyclonic shear of anomaly wind fields in eastern part of northwest China lead to more rain. While the general circulation characteristics of less rain were negative-positive- negative anomalous distribution from west to east in high latitudes in Europe and Asia, stronger long wave ridge at Central-Asian, weaker and position by east of western Pacific subtropical high. It was hot and dry weather in Shaanxi controlled by northwest flow of Central-Asian ridge. But it was wet day when East-Asian summer monsoon was weak, East Asia mid-latitude was prevailing straight westerly flow, westerly jet located at 40°N, location of the western Pacific subtropical high was to the south and west as compared with the normal, Tibetan plateau potential height was lower than normal and more short wave trough or low-pressure system. The westerlies system and low pressure system of plateau east shift had impact on the summer more rain in Shaanxi Province.