A Study of Determination Index of Regional Meiyu over the Yangtze－Huaihe Basin

In order to determine the Yangtze－Huaihe regional Meiyu and develop its relating short-term climate prediction operation, based on the regional Meiyu concept, a new index of determining Yangtze－Huaihe regional Meiyu is firstly put forward according to regional Meiyu's large-scale durative characteristics of both temporal and spatial distributions after 36 typical stations over the Yangtze－Huaihe region are selected. The percentage of station coverage satisfying rainfall days≥4 for 5 consecutive running pentads is adopted combining with the location of the western Pacific subtropical high ridge in the definition of the Meiyu criteria. The climatic features of regional Meiyu are then analyzed on the basis of determined regional Meiyu. And those features are compared with Meiyu over the middle and lower reaches of the Yangtze River. Results indicate that the new index can well describe climatic characteristics of regional Meiyu on both large-scale continuous rainfall phenomenon and high-low levels circulation configuration of Meiyu system. Meanwhile, comparison of different regional Meiyu indexes suggests that the climate feature, long-term change, and abnormal Meiyu years reflected by the new index are in common with the existing Meiyu data for the middle and lower reaches of the Yangtze River. However, the new index defined in this paper is superior to the Yangtze River Meiyu index defined by the observations at five stations in some respects such as coherence of circulation adjustment, representation of regional Meiyu depicted by 36 observational stations with uniform spatial distribution, and so on.