The Relationship Between Meridional Anomaly Of East Asian Winter Monsoon And The Later Meiyu Precipitation In Zhejiang

4 main kinds of Meiyu precipitation distribution in Zhejiang are analyzed by using EOF and REOF method,and their spatial characteristic is remarkable on interdecadal scales.After the 80s,the different Meiyu precipitation distribution in Zhejiang tends to change in the same phase and the change between regions is strengthening.The interannual and interdecadal periods of Meiyu precipitation distributions in Zhejiang are revealed by Wavelet analysis.Cold air is one of the main influences for the distributions of Zhejiang Meiyu precipitation.The meridional (zonal) circulation in mid and high latitude will benefit(disbenefit) the cold air influence southwest,northwest and northeast of Zhejiang,which favors(disfavors) the meiyu precipitation.Using NCEP Sea Level Pressure reanalyzed monthly average data,a winter monsoon meridional change index is defined to show the intensity difference of winter monsoon between mid and high latitudes.The index agrees well with the east Asian winter monsoon index.Generally,when the winter monsoon meridional change index(WMMCI) is stronger,the east Asian winter monsoon index(EAWMI) is stronger,and the WMMCI is weaker when the EAWMI is weaker,too.Also,their interdecadal correlation are obviously.The correlation between the WMMCI index and the later Meiyu precipitation in Zhejiang was studied.And the results show that the abnormality of East Asian winter monsoon affects Meiyu precipitation in northwest Zhejiang greatly.The Meiyu in northwest Zhejiang will mostly be heavy(light) when the preceding winter monsoon is strong(weak).There is a positive correlation between the WMMCI and later Meiyu in Zhejiang on both interannual and interdecadal scales,the interdecadal correlation is remarkable than interannual correlation.Moreover the influence following after the meridional abnormality of winter monsoon will last two or three years,the variation trend of northwest Zhejiang's Meiyu precipitation is behind that of the index.The Meiyu precipitation in northwest Zhejiang will continually be heavy(light) when WMMCI has continually strengthened(weakened) for 2 years and the winter monsoon is strong(weak).The effect on later precipitation caused by weak winter monsoon is slower than that caused by strong winter monsoon. Composite analysis shows that the meridional change characteristic of winter monsoon is obviously in the Sea Level Pressure fields in the preceding winter.The pattern of north positive(negative) and south negative(positive) in 500hPa height favors the development of meridional(zonal) circulation over mid and high latitudes. The meridoinal(zonal) circulation will benefit(disbenefit) the southward movement of the cold air.Also the pattern has a persistent effect on the circulation,which favors (disfavors) the meiyu precipitation.A possible explanation for the continual effect of the winter monsoon's meridional abnormality on Meiyu precipitation in northwest Zhejiang is that the continually strengthening(weakening) strong(weak) winter monsoon causes the abnormality of westerly(easterly) in the equatorial Pacific Ocean, which will trigger the happening of El Nino(La Nina) and affect the atmospheric circulation continually in the later time.