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.