印度洋海盆模影响西北东部降水的大气环流分析

Analyses of Atmospheric Circulation of Tropical Indian Ocean Basin Mode Influencing Precipitation in East of Northwest China

利用回归统计方法分析了热带印度洋海盆模影响西北地区东部5月降水异常的大气环流异常分布及可能的物理机制。结果表明:印度洋暖海盆模可以在亚欧地区大气中引起类似"Matsuno-Gill Pattern"的大气响应,在对流层中上层形成异常波列,西北地区东部正好位于新疆—巴尔喀什湖负异常中心和东亚地区正异常中心之间,处在明显西低东高的高度场异常形势下,这正是西北地区东部5月降水异常偏多的典型环流形势。对应波列分布,欧亚范围存在3个明显异常气旋、反气旋,对流层高层200 h Pa华北到西北地区东部为大片气流异常辐散区,低层850 h Pa为气流辐合,形成异常垂直上升运动,有利于西北区东部降水异常偏多。因此印度洋海盆模是通过引起遥相关波列,在西北地区东部上空形成西低东高的异常环流,从而影响该地区的降水异常。

Our previous study shows that since mid 1970 s the persisting anomaly of the tropical India Ocean Sea Basin M ode( IOBM) in previous winter and spring is significantly corrected with precipitation anomaly main mode in the East of Northwest China( ENC) in subsequent M ay. In this study,using regression method,the atmospheric circulation anomaly and possible mechanism of the IOBM influencing on precipitation in ENC are studied. It is found that the warming IOBM can induce the responding of ‘M atsuno- Gill Pattern'in the atmosphere and form the wave train over area from the tropical Indian Ocean to Europe to Asia at middle to upper troposphere level. The anomalous values of wave train increase with height increasing. ENC is just located between the negative center of Xinjiang to Balkhash Lake and positive center of East Asia,and just controlled by the pattern of ‘West Lowand East High',which is the typical circulation pattern of more precipitation in ENC. Corresponding to the wave train of height anomaly,there are three significant cyclone and anticyclone anomaly centers over Europe- Asia area. At upper level of 200 h Pa,it is the large scale wind divergence anomaly over area from North China to ENC,and at lower level of 850 h Pa it is the convergence over there. Concerned with the divergence at upper level and convergence at lower level,it induces the vertical ascending,which is advantage of more precipitation. The vertical ascending motion center is over area from North China to ENC. So it is said that the IOBM can influence the precipitation anomaly over ENC by inducing the wave train over Europe to Asia area at middle-upper troposphere,and informing anomaly circulation pattern of ‘West Lowand East High 'over ENC. For the cold case of IOBM,it is vise verse.