Possible Influences of ITCZ in Asian Monsoon Regions on Rainy Season Anomaly of North China

Vast convective activities over tropical zones are analyzed for both wet and dry summers in North China. An ITCZ synthesis index is designed using OLR data. The index can demonstrate quite clearly and objectively the seasonal featurea of deep convection in Asia monsoon areas. The differences of ITCZ activi ties in Indian as well as East Asian monsoon regions in winter-spring period are significant and so is the time-lagged correlation, which would be able to provide a new way to the long-lead prediction of summer rain in North China. The propagation characters of low frequency fluctuation are also different between wet and dry years. The intensity of low frequency fluctuation is stronger and the area is larger in wet years than that in dry years in both hemispheres. The fluctuation moves from south to north successively in wet years, which may lead to the leap of the subtropical high northwards, while it remains quasi-stationary in the Southern Hemisphere or the equatorial zone in dry years.