Impacts of Cross-equatorial Flow on Subtropical High Ridge Jumping Northward to 25°N
Using 850hPa mean monthly wind data, as well as data of 500hPa height, date of the Western Pacific Subtropical High ridge jumping northward to 25°N and precipitation data from June to July at 25 representative weather stations in Fujian, the criteria for the anomalous date of the subtropical high jumping northward to 25°N are defined and the anomalous years are found, the general characteristics of 850hPa wind field in June of the anomalous years are analyzed with the composite analytical method, and the effects of intensity of the Somali cross-equatorial flow on the subtropical high northward jumping to 25°N are discussed. The results are as follows: The Somali cross-equatorial flow with above-normal (below-normal) intensity in June contributes to the subtropical high jumping northward to 25°N earlier (later). The correlative coefficients between intensity of the Somali cross-equatorial flow from May to June and 500hPa heights in mid latitudes over the region from East Asia to the western Pacific are positive. The favorable circulation for the subtropical high northward jumping to 25°N earlier (later) is the higher (lower) heights in the region. Intensity of the Somali cross-equatorial flow could be a signal for predicting the time when the subtropical high jumps northward to 25°N. Based on the above results, the date of the subtropical high jumping northward to 25°N is diagnosed. It shows that the diagnosed result is correct.