1999年北半球大气环流特征及其影响

１９９９年北半球主要环流特征为：５００ｈｐａ西太平洋副热带高压较常所明显偏弱，春、夏季副高位置异常偏东；东亚地区夏季５００ｈｐａ位势高度距平场上表现为北高南低，大陆高压较强。亚洲中纬度经、纬向环流交替出现，阶段性明显；冬季冷空气异常偏弱，东亚夏季风加强。冬、春季热带对流活动强盛，入夏以后迅速减弱。在Ｌa－ｎｉｎａ和大气 环流的共同影响下我国天气气候发生了明显异常。

General Circulation and Its Impact over the Northern Hemisphere in 1999

General circulation features over the Northern Hemisphere in 1999 were analysed.It is shown that the 500hPa subtropical high over the west Pacific was weaker than that of last year.Its ridge point is anomaly to the east in spring and summer.At 500hPa,zonal and meridional circulation take place by turn,cold air is weaker than normal in winter.Monsoon is stronger during summer.The convection activity is strong during winter and spring,and it is weaker in tropics in summer.A strange La Nina event is persisting in the tropical Pacific region in 1999.The anomaly of both the tropical Pacific and atmosphere circulation exerted a significant impact on weather and climate in China.