赤道中东太平洋关键区海温对宁夏春季降水的影响

Effect of equatorial east Pacific SST of key areas on spring rainfall in Ningxia

基于宁夏全区范围内24个常规气象站近53 a春季降水量资料和美国气候预测中心1961-2013年Nino1＋2和Nino3.4月平均海平面温度指数资料及NCEP/NCAR北半球月平均500h Pa高度距平场再分析资料,采用经验正交函数分解（EOF）及滑动相关分析方法,对宁夏逐年春季降水量的空间分布进行分型,并分析了各空间分布型的时间演变特征,进一步研究了赤道中东太平洋关键区（Nino1＋2、Nino3.4）海温是如何通过对西太平洋副高及500 h Pa中高纬大气环流的影响来影响宁夏的春季降水。结果表明：近53 a来,宁夏春季降水全区一致偏多或偏少分布型的占比超过70%,21世纪后全区降水一致偏少型明显减少;前一年夏秋季节赤道中东太平洋关键区海温与次年宁夏春季降水存在持续5~8个月的显著高相关,其中7~9月相关最显著,且相关程度逐步提高;研究发现,前一年夏秋季节,赤道中东太平洋关键区海温异常,通过海气相互作用,对次年春季北半球500 h Pa高度距平场上中高纬度大气环流的配置以及西太平洋副热带高压的位置产生明显的影响,近而影响形成次年春季宁夏降水的水汽来源以及空间分布。因此,这些前期的稳定强信号对宁夏春季降水预测具有明确的指示意义。

Based on data of Ningxia 24 meteorological stations spring precipitation in recent 53 years,Nino1＋2and Nino3.4 index of monthly mean sea surface temperature（SST）in the period of 1961-2013 obtained from American climate forecast center,and reanalysis monthly 500 h Pa height form NCEP/NCAR,using empirical orthogonal function（EOF）and running correlation analysis methods studies the spatial distribution and time evolution of spring precipitation in Ningxia,and studies furtherly how the Pacific SST in the key area of the Equator middle-east influence the precipitation through the western Pacific subtropical high and 500 h Pa atmospheric circulation over middle-high latitude. The study result shows that,in recent 53 years,the uniform more or less precipitation anomaly patterns of spring precipitation in Ningxia accounts for more than 70%,in which the uniform less pattern accounts for 43% and uniform more pattern accounts for 27%. The second anomaly pattern is of north less and south more precipitation,which accounts for 21%,and the opposite pattern accounts for 7%. In further it finds that the key area SST of Equator middle-east Pacific in previous summer-autumn persisting correlates significantly to the subsequently spring precipitation in Ningxia during 5-8 months. The correlation coefficients are higher to the previous July to September SST with correlation coefficients gradually increasing. Through air-sea interaction,the key area SST anomalies of Equator middle-east Pacific influence the 500 h Pa height anomaly atmosphere circulation and location of the western Pacific subtropical high,and these two influence the water vapor sources and spatial distribution of subsequently spring precipitation of Ningxia. Corresponding to years of previous summer-autumn warmer SST in Nino1＋2 area of equator middle-east Pacific,in the subsequent spring,it is always found the positive and negative height anomaly centers,e.g. ＋- ＋ pattern on 500 h Pa level in the middle-high latitude,with negative height anomaly over a wide region around Baikal Lake and west of there. And accompanying with trough depth and Ningxia locates in front of it and positive anomaly near Japanese sea. Then it forms the west low and east high pattern,which is advantage of the forming stable precipitation. If the previous SST is cooler,the East Asian trough depths on 500 h Pa level in subsequent spring,in this atmosphere circulation configuration pattern Ningxia locates in west high and east low pattern,which is not advantage to precipitation.In further through statistic it is found in most cases,if previous year summer-autumn Nino1＋2 SST anomaly is warmer,in the subsequent spring the Western Pacific subtropical high ridge line position and the northern boundary is normal north,west ridge point obviously to the west,with more than 50% years to 100°E West,and Ningxia is in the southwest airflow of the west side of the West Pacific subtropical high,which is advantage to precipitation. If previous summer-autumn Nino1＋2 SST anomaly is cooler,in the subsequent spring the northern boundary of Western Pacific subtropical high is significant south and ridge line position normal south,west ridge point obviously to the east,with more than 50% years to 100°E east,and in which 42% years is over around 166°E. In this case the water vapor channel is blocked and not advantage to induce precipitation.