A Mechanism for the Impact of Sea Surface Temperature Anomaly over Tropical Pacific and Indian Ocean on East Asian Winter Monsoon

After the relationship between sea surface temperature anomaly(SSTa) over tropical Pacific and Indian Ocean and East Asian winter monsoon(EAWM) had been analyzed with atmospheric circulation and SSTa data provided by NCEP/NCAR,an Index reflecting the co-variation of sea surface temperature anomaly over tropical Pacific and Indian Ocean was introduced.The analysis results indicted that,when the index is larger(smaller) than normal,the EAWMI is often larger(smaller) than normal,and the abnormal south(north) wind appears over East Asia,which leads the EAWM is weaker(stronger) than normal.The mechanism was obtained with simple model considering the impact of heating on tropical atmospheric circulation.The result shows that the abnormal south(north) wind will be forced out when the SSTa index is in positive(negative) phase,which is one of the most significant impacts on EAWM.The tropical Western Pacific is the key area which influences the EAWM.