与ENSO有关和无关年江、淮旱涝可能成因研究

STUDY ON CAUSES OF DROUGHT AND FLOOD OVER THE HUAIHE AND MID-LOWER YANGTZE VALLEYS DURING THE SUMMERS WITH AND WITHOUT ENSO

利用Nio 3指数,把ENSO循环不同位相的夏季划分为四类并进行聚类分析,发现E1 Nio发展期和La Nia衰减期可以聚为一类;E1 Nio衰减期和La Nia发展期可以聚为一类。而后经过比较分析,考虑ENSO循环对江、淮地区降水的不同影响,定义了新的东亚副热带夏季风强度指数。并利用该指数研究了夏季风异常和ENSO循环与江、淮地区夏季降水年际变化的关系和成因。结果发现,ENSO年,淮河和长江中下游地区夏季降水的年际变化是ENSO和夏季风共同作用的结果。ENSO的不同位相对雨带的南北位置有重要影响,夏季风异常主要对雨量的偏多偏少起重要作用。而与ENSO无关的年份,易出现强夏季风,这种年份长江和淮河地区经常是一致的干旱。

By using Nino 3 index,the summers during the different phases of the ENSO cycle are divided into four types. Then based on the summer rainfall data of the Huaihe and mid-lower Yangtze valleys,using the cluster analysis method,we find that the developing（decaying） phase of E1 Nino and the decaying（developing） phase of La Nina belong to the same type. Then according to the different influences of the ENSO cycle on the rainfall over the Huaihe and mid-lower Yangtze valleys,a new East Asian subtropi- cal summer monsoon index is developed. And by using of the index,it is found that during an ENSO period the interannual variation of the summer rainfall in the two regions is due to the interaction between the ENSO cycle and the summer monsoon. The ENSO cycle enables the rainband＇s position to change through influencing the range of the East Asian summer monsoon anomalies, however, the strength of the East Asian summer monsoon mainly changes the rainfall over the two regions. However, during the years without ENSO,it is the strength of the East Asian summer monsoon that mainly determines the rainfall in the two regions .