前期季节内振荡对云南5月降水的影响  

THE INFLUENCE OF PRECEDING INTRASEASONAL OSCILLATION ON THE PRECIPITATION IN MAY OVER YUNNAN

作　　者：李汀[1] 严欣[2] 琚建华[3] 

机构地区：[1]中国科学院大气物理研究所/大气科学和地球流体力学数值模拟国家重点实验室,北京100029 [2]云南大学资源环境与地球科学学院,云南昆明650031 [3]云南省气象局,云南昆明650034

出　　处：《热带气象学报》2013年第3期489-496,共8页Journal of Tropical Meteorology

基　　金：国家公益性行业(气象)专项(GYHY201306022);灾害天气国家重点实验室开放课题(2012LASW-A02)共同资助

摘　　要：采用OLR和风场再分析资料及降水资料，发现一个与云南雨季5月降水显著相关的关键区（77．5～82．5°E，5～10。N），关键区内OLR低频振荡（Ikey）在4月2—3候的平均值（Ikey-Apr）与云南5月降水具有显著负相关，云南5月多雨年时为负值（低频对流活跃），少雨年时为正值（低频对流受抑制）。多雨年时，关键区在4月2—3候出现的强低频对流标志着亚洲热带季风开始在关键区建立并进入ISO（季节内振荡）活跃期，约20d后的4月末一5月初关键区低频振荡再次进入活跃位相，激发西南季风沿西南一东北方向传播并向云南输送水汽，当低频对流传到云南后，西南季风在云南建立，云南较早进入雨季，5月降水迅速增多。而当关键区低频信号于4月末一5月初较晚出现时，第二次低频对流和西南季风ISO的东北向传播也随之推迟，夏季风在云南建立和云南雨季开始偏晚，5月降水偏少。把Ikey-Apr作为云南雨季开始早晚和降水多寡的前兆信号。云南5月多雨年从4月第4候-5月第5候，低频对流在云南形成了一个完整波型，5月第1候前孟加拉湾和云南处于低频对流抑制区控制下，西南向水汽输送未形成。5月第l候后关键区低频对流开始向西北．东北向传播，孟加拉湾低频西南风加强，暖湿气流逐渐传向云南，西南季风在云南建立，雨季提前开始，降水迅速增多。Using OLR and wind reanalysis data and precipitation data, this paper discovers a key area （77.5-82.5 °E, 5-10 °N） that shows significant correlation with Yunnan precipitation in May. LF （Low Frequency） OLR in the key area （/key） during pentads 2--3 of April （Ikey-Apr） shows significant negative correlation with the Yunnan precipitation in May. Ikey-Apr is negative in years of excessive May rain in Yunnan but positive in drought years. In years of excessive rain, strong LF convection in the key area in these pentads of April marks the establishment of the tropical Asian Monsoon （AM） in the key area and ISO （Intra-Seasonal Oscillation） entering the active phase. About 20 days later, this LF convection enters the active phase again. From the end of April to the beginning of May, the Southwest Monsoon is excited to propagate along the southwest-northeast direction and transport water vapor to Yunnan. When the LF convection arrives in Yunnan and the Summer Monsoon establishes in Yunnan, its rainy season starts earlier and precipitation increases in May. However, when the LF signal in the key area appears at the end of April and the beginning of May, the second LF convection and the northeastward propagation of Southwest Monsoon ISO are also delayed, and the Summer Monsoon establishes in Yunnan and its rainy season begins at a later date, with decreased precipitation in May. Therefore, Ikey-Apr is precedent that signals whether the Yunnan rainy season will start early or late and whether its precipitation will be more or less. During the 4th pentad of April through the 5th pentad of May in years of excessive rain, ISO in Yunnan forms a complete wave. Before the 1st pentad of May, BOB （the Bay of Bengal） and Yunnan are controlled by repressed LF convection, and southwest water vapor transportation has not formed yet. From the 1 st pentad of May, the LF convection in the key area moves northeastward, LF southwest wind in BOB strengthens, and warm and wet currents propagate to Yunnan. As a r

关 键 词：季节内振荡 云南5月降水 低频OLR 孟加拉湾西南季风 

分 类 号：P426.616[天文地球—大气科学及气象学]