The Relationship Between East Asian Winter Monsoon Meridional Anomaly and Meiyu Precipitation of Jiaxing

Using NCEP/NCAR reanalysis monthly average SLP data, a winter monsoon meridional change index (WMMCI) is defined to show the intensity difference of winter monsoon between mid and high-latitudes. The index is well in accordance with the East Asian winter monsoon index (EAWMI). Generally, when WMMCI is strong, so is EAWMI. And WMMCI is weaker when EAWMI is weaker, too.The correlation between WMMCI and Meiyu precipitation of Jiaxing is studied. The results show that the abnormal Meiyu precipitation in the coming summer is caused by the abnormality of East Asian winter monsoon and the influence lasts two or three years. There is a positive correlation between the WMMCI and later Meiyu precipitation of Jiaxing on both interannual and interdecadal scales. Jiaxing Meiyu precipitation is generally heavy (light) when preceding winter monsoon is strong (weak). The variation trend of the Jiaxing Meiyu precipitation is behind the index. The Meiyu precipitation of Jiaxing is continuously heavy (light) when WMMCI continuously strengthens (weakens) 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.The composite anomalies of 500 hPa height show that the development of meridional (zonal) circulation over mid-and high-latitudes is favored by the pattern of north positive (negative) and south negative (positive). The southward movement of the cold air is benefited (not benefited) by the meridoinal (zonal) circulation. Also, the pattern has a persistent effect on the circulation, by which the Meiyu precipitation is favored (not favored). A possible explanation of the continuous effect of the winter monsoon meridional abnormality on the Meiyu precipitation of Jiaxing is that the abnormality of westerly (easterly) in the equatorial Pacific Ocean is caused by the continuously strengthening (weakening) strong (weak) winter monsoon, by which the occurrence of El Niño (La Niña) through abnormal variation in sea surface temperature is triggered.