北半球夏季环流持续性异常及其发展特征

Persistent Anomalies in the Northern Hemisphere during Summer Time and Characteristics of Their Development

利用美国国家气象中心（ＮＭＣ）的１９５７～１９７９年夏季５００ｈＰａ位势高度场，分析了热带外地区环流持续性异常。夏季持续性环流相当活跃，但异常（≥４０ｍ）的持续时间小于１个月。不同地区的持续异常极少能同时存在，主要表现为单独发生。持续异常具有遥相关结构，它们在相当程度上同冬季遥相关型相似。持续异常建立过程中主要中心强度增长相当快，振幅加倍时间约为２天。持续异常的建立，对最优扰动的发展具有重要作用。

An analysis of persistent anomalies in the extra-tropical areas is presented based on the data of 500 hPa potential height of 23 years from 1957 to 1979 from American NMC (National Meteorological Center) Persistent anomalies are considerably active in summer, but the lasting time of the anomalies with larger than 40 m is less than one month Persistent anomalies in different geographical regions are little possible to coexist, and their structures are characterized in teleconnection patterns, which resemble those in winter In the formation process of persistent anomalies, the intensity of main centers of perturbation increases with large growth rates in which the time of doubling intensity is about 2 days It is suggested that optimal perturbations play a crucial role in the development of persistent anomalies