Persistent Anomalies in the Northern Hemisphere during Summer Time and Characteristics of Their Development
北半球夏季环流持续性异常及其发展特征

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