Climatic Characteristics Of Extratropical Cyclone Activity And Its Anomaly Over East Asia And West Pacific During Recent 50 Years

By use of NCEP/NCAR daily reanalysis sea level pressure data from 1948 to 2002 and height data from 1949 to 2002,monthly rainfall and temperature of 160 stations from 1951 to 2000 in china and SST data from Hadley Centerthe, climatic characteristics of Extratropical Cyclone frequency as well as the relationships with SST have been computed and analyzed.The result indicates that the change trend of Northern Cyclones and Southern Cyclones are contrary with the year,but the change trend of Southern Cyclone is more notable.Monthly variation of Northern Cyclones and Southern Cyclones have evident difference with two peaks in Northern Cyclones monthly frequency ,but with one peak in Southern Cyclones,moreover,their lowest values appear in winter.The zone distribution are also different between Southern Cyclones and Northern Cyclones,namely, Nouthern Cyclones mostly appear on the continent and Southern Cyclones on the sea or edge of the sea.The area of most Northern Cyclones frequency locate Mongolia and Northeast of china,however, that of Southern Cyclones locate the sea and the edge of sea.During half century,their frequencies appear two different evidently stages,and more analysis has indicated that Northern Cyclones frequency occur break in the middle of 1970s because 500hPa height field experienced the decadal climatic break.There are consistent relationship between the frequencies of Northern Cyclones and Southern Cyclones and ENSO events,namely,their frequencies is less when El Nino events happen and more when La Nina events happen,but ENSO events have great influence on the frequencies of Southern Cyclones whether it is seen from climatic probability or the judgement of difference's notablility.From two typical years of the most and least Southern Cyclones frequencies,their SST distributions appear to be contrary begin with April.The relationship between Southern Cyclones frequencies and the SST in the east of equator pacific in the last year,especially in spring,is very well,and they show positive correlativity.The flourishing season of Extratropical Cyclone Frequency usually bring determinate influence to China whether in the south or in the north.When Northern Cyclones frequencies in spring is on the more(less) side,the rainfall is on the less(more) side for the most part of North china as well as the north of Sinkiang; whereas the temperature is descend(ascend) in some partsof Gansu,Ningxia,Shanxi and Neimeng. In spring.the descending frequencies of Northern Cyclones from 1980s to 1990s have resulted the reduce of frequencies of sandstorm contrast to the 1970s.There are consanguineous relationship between Coastal Cyclone activity frequency in China in June and July and the precipitation in the middle and backward position of the Changjiang River,when coastal cyclones frequencies is more,the rainfall is more in the middle and backward position of the Changjiang River,so it is proved that Coastal Cyclone activity frequencies have specific token ability for the research of region rainfall.