梅雨锋云系的模态研究I：主导模态

利用经验正交函数（EOF）分解方法，对1998～2008年梅雨活跃期共16次过程每3 h间隔的静止卫星云顶亮温（也称相当黑体亮度温度，即Black Body Temperature，以下简称TBB）的距平场进行计算，获得了梅雨锋云系的主要模态。经检验，前7个模态为独立模态，方差贡献分别为7.78%、5.83%、5.20%、4.27%、4.19%、3.62%和3.36%。这7个独立模态反映梅雨期间云系主要的异常特征。各模态相似云图中的云系与气候态相比出现位置偏移与形状变化，表明梅雨锋云系随主导环流系统的演变而发生断裂、减弱、消散、重建的过程。从各模态相应的大气环流配置来看，气候态梅雨锋云系对应的大气环流为三阻型梅雨形势。另外7个主导模态的大气环流基本可以划分为两类，一类为阻塞高压型，中高纬地区存在阻塞高压活动，在第2模态正位相，第4模态负位相，第5模态正位相和第6模态正、负位相以及第7模态正位相对应的500 hPa环流形势上都可以看到这一特点；另一类为槽脊型，中高纬地区阻塞高压活动不明显，等高线为一槽两脊或两槽一脊型分布，与这种环流形势相关的模态有第1模态正、负位相，第2模态负位相，第3模态负位相，第4模态正位相，第5模态负位相和第7模态负位相。

Modes of Meiyu Frontal Cloud Systems. Part I:Dominant Modes

The empirical orthogonal function (EOF) is applied to the 3-h interval black body temperature (TBB) from three geostationary satellites in the active periods of Meiyu during 1998-2008. The first seven independent leading modes (EOF1 to EOF7) of the Meiyu frontal cloud are extracted, and the variances explained by these modes are 7.78%, 5.83%, 5.20%, 4.27%, 4.19%, 3.62%, and 3.36%. These seven independent leading modes reflect cloud anomalies during the main rainy seasons. In contrast to the climatological Meiyu front cloud system (MFCS), the most similar cloud images for each leading mode show significant position shifts and shape changes, indicating the evolution of fracture, weakening, dissipation, and rebuilding of the MFCS.Circulation configuration for the climatological MFCS is the three-resistance highs type. In addition, two typical circulation types are noted for the seven leading modes of the MFCS. The first type is the resistant high, in which the middle and high latitudes are occupied by a blocking high. This characteristic is evident in the positive EOF2, EOF5, EOF6, and EOF7 as well as the negative EOF4 and EOF6. In the second type, one trough and two highs or one high and two troughs occur in the middle and high latitudes of 500 hPa. This circulation type is often companied by positive EOF1 and EOF4, as well as negative EOF1, EOF2, EOF3, EOF5, and EOF7.