PDF《东亚夏季风爆发和北进的年际变化特征及其 与热带西太平洋热...》

1 期2005 年1月大气科学Chinese Journal of Atmospheric Sciences Vol. 29,No.

1 Jan.

2005 western Pacific along 137?E and the NCEP/NCAR reanalysis data. The results show that when the tropical western Pacific is in a warming state in spring,convective activities are intensified around the Philippines. In this case,there is a cyclonic anomaly circulation in the lower troposphere over the South China Sea,and the western Pacific subtropical high shifts eastward,thus,the early onset of the South China Sea summer monsoon (SCSM)can be caused. Moreover,when the tropical western Pacific is also in a warming state,convective activities around the Philippines are also strong in summer,since the western Pacific subtropical high abruptly shifts northward in mid-June and early July during its northward advance in this case,the abrupt northward-shift of the East Asian summer monsoon rainband from South China to the Yangtze River and the Huaihe River valleys is obvious in mid-June and this monsoon rainband again jumps northward from the Yangtze River and the Huaihe River valleys to the Yellow River valley,North China and Northeast China in early July. This can cause that summer monsoon rainfall is below normal and drought may occur in the Yangtze River and the Huaihe River valleys and the middle and lower reaches of the Yangtze River,but summer rainfall is normal or above normal in the Yellow River valley,North China and Northeast China. On the other hand,when the tropical western Pacific is in a cooling state in spring,convective activities are weakened around the Philippines. In this case, there is an anticyclonic anomaly circulation in the lower troposphere over the South China Sea,and the western Pacific subtropical high shifts westward,thus,the late onset of the SCSM can be caused. Moreover,when the tropical western Pacific is also in a cooling state,convective activities around the Philippines are also weak in summer,since the abrupt northward-shift of the western Pacific subtropical high is not obvious in mid-June and early July and it gradually shifts northward during its northward advance in this case,the East Asian summer monsoon rainband can be maintained in the Yangtze River and the Huaihe River valleys. This can cause that the summer monsoon rainfall is above normal and flood may occur in these two valleys,but summer rainfall is below normal and drought may occur in the Yellow River valley, North China and Northeast China. It is also explained by using the dynamical theory of nonlinear multiple equilibrium that the strong or weak convective activities around the Philippines play an important role in the abrupt or gradual northward shift of the western Pacific subtropical high. Key words summer monsoon,interannual variation,the tropical western Pacific subtropical high,convective activity

1 引言 今年

2 月21 日是叶笃正院士的

90 华诞.叶笃正 院士是世界著名的气象学家,也是中国现代大气科学 主要奠基人之一.他在 Rossby 波的能量频散、大气 运动的适应过程、东亚大气环流的演变特征与机理、 青藏高原的动力、热力作用以及全球气候变化和可持 续性发展等研究领域作出了系统而开创性贡献. 我国地处东亚季风区,东亚季风的变异严重影响 着我国旱涝气候灾害的发生,从而给我国带来严重的 经济损失,为此,中国气象学者很早就重视对东亚季 风的研究.早在

60 年前,我国著名气象学家竺可 桢[1] 首先提出东亚夏季风对中国降水的影响,之后, 涂长望和黄仕松 [2] 研究了东亚夏季风的进退对中国降 水季节内变化的影响.为了改进中国的天气预报,提 高其预报水平,叶笃正院士继竺可桢、涂长望和赵九 章先生之后,对东亚大气环流的变化特征和机理作了 系统而开创性的研究 [3 ~ 11] .叶笃正等 [12] 早在