孟加拉湾西南季风与南海热带季风季节内振荡特征的比较

A comparison of intra-seasonal oscillation characteristics between the southwest monsoon of the Bay of Bengal and the South China Sea summer monsoon.

采用美国国家环境预报中心的向外长波辐射和风场资料及日本气象厅的降水资料,用30 60 d滤波后的夏季风指数在孟加拉湾和南海的区域平均值分别代表孟加拉湾西南季风和南海热带季风季节内振荡,对两支季风的季节内振荡特征进行比较分析,发现孟加拉湾西南季风的季节内振荡和南海热带季风的季节内振荡在夏季风期间(5-10月)都有约3次半的波动。夏季风期间,在阿拉伯海—西太平洋纬带上,夏季风的季节内振荡有4次从阿拉伯海的东传和3次从西太平洋的西传,其中7月后东传可直达西太平洋。孟加拉湾和南海在夏季风期间都有4次季节内振荡的经向传播,但孟加拉湾在约15°N以南为季节内振荡从热带东印度洋的北传,在约15°N以北则为副热带季风季节内振荡的南传;而在南海则是4次季节内振荡从热带的北传。在以孟加拉湾西南季风季节内振荡和南海热带季风季节内振荡分别划分的6个位相中,都存在1—3位相和4 6位相中低频对流、环流形势相反的特征,这是由热带东印度洋季节内振荡的东传和北传所致。热带印度洋季节内振荡沿西南东北向经过约14 d传到孟加拉湾,激发了孟加拉湾西南季风季节内振荡的东传,经过约6 d到达南海,激发了南海热带季风季节内振荡的北传,经过约25 d到达华南,形成热带印度洋季节内振荡向华南的经纬向接力传播(45 d)。孟加拉湾西南季风季节内振荡所影响的降水主要是在20°N以南的热带雨带随低频对流的东移而东移;而南海热带季风季节内振荡所影响的降水除了这种热带雨带随低频对流的东移外,还有在20°N以北的东亚副热带地区存在雨带随南海低频对流的北移而北移。

Adopting the outgoing longwavc radiation （OLR） and wind data of NCEP and the precipitation data of Japan,and using the filtering summer monsoon index（Im）in 30-60 d averaged over the area of the Bay of Bengal（BOB） and the area of the South China Sea （SCS） respectively to present the Intra-Seasonal Oscillation（IS0） of the Southwest Monsoon（SM） of BOB and the South China Sea Summer Monsoon （SCSSM）,the 7S0 features of the two monsoons are compared.The ISOs of SM of BOB and of SCSSM have 3 and half times of ISO waves during the summer monsoon period （May-Oetober）.Along the zone of the Arabian Sea-West Pacific, there are 4 times of summer monsoon ISO eastward propagation from Arabian Sea and 3 times of westward propagation from the western Pacific.After July, the westward propagation of ISO is inhabited and the cast-ward propagation can arrive to the western Pacific.（hhere are 4 times of meridional propagation of monsoon ISO in both the areas of BOB and of SCS during the monsoon period.In the area of BOB, it is northward propagation from the tropic eastern Indian Ocean south of around 15°N, and is southward propagation of sub-tropical monsoon ISO north of around 15°N.However, in SCS, it is 4 times of northward propagation of the monsoon ISO from the Tropic.Both in the respective 6 phases of ISO of SM of BOB and of IS0 of SCSSM,there is opposite-phase feature of the LF convection and circulation in the phase 1-3 to that in phase 4-6,which is caused by eastward and northward movement of IS0 in the tropic eastern Indian Ocean.The LF convcction propagates along the southwest-northeast direction from the tropic eastern Indian Ocean to BOB （needing about 14 d）,exciting the ISO of SM of BOB, and then propagates eastward to SCS （needing about 6 d） to excite the ISO of SCSSM.It takes about 25 d for the ISO of SCSSM to propagate to South China with the result that the meridional and tonal relay propagation of ISO from the tropic Indian Ocean to South China experiences about 45 d.（hhe precipitation belt impacted by SM of BOB moves eastward with the LF convection south of 20°N,but the precipitation belt impacted by SCSSM,in addition to the above,also moves northward with the LF convection of SCS north of 20°N.