The Indian Ocean Dipole And Its Relationship With Precipitation Over China

Based on globel monthly mean SST data from Hadley center, NCAR/NCEP reanalysis data and the 160 stations rainfall in China, the relationship between the India Ocean Dipole( IOD) and rainfall both in summer and autumn over China is discussed. The impact of ENSO on the rainfall and the wanner SST in Indian Ocean recently are considerd in the paper. By analysis the anomalous atmosphere circulation caused by IOD, the reasons for rainfall anomaly over China during IOD time are found out The main results are:(1) To sum up(take the positive phase as example), the positive phase of IOD may make the south to Yangtze River rainfull, and the north rainless in summer while make the southwest of China rainfull in autumn. In summer, the positive phase of IOD is favorable for the stronger southwest monsoon, the stronger South China Sea monsoon, and a weaker subtropical high, which all make precipitation over south of China increasing in summer. In autumn, a stronger southwest current make the south of China rainfull. The vertical circulation anomaly shows that the positive phase make for a weaker zonal vertical(Walker) circulation, which makes for a weaker meridional vertical(Hadley) circulation further and makes for rainless in south of China.(2) Based on conclusion of (1), ENSO plays a negative role to the correlation of IOD and precipitation in the southwest of China and Jianghuai area while plays a positive role to that in the southeast and the north of China in summer. ENSO also has the same effect with IOD to the precipitation in the southwest, while has opposite effect to the Yellow reach in autumn. ENSO is favorable for the weaker India monsoon, a weaker South Asia high, the weaker East Asia subtropical monsoon and subtropical high sorthward. In autumn, ENSO induce a stronger southwest current, the weaker convective acivities around the Philippines and subtropical high sorthward.(3) Based on conclusion of (1), The warming of India Ocean SST in the interdecadel scale influence the relationship of IOD and precipitation over China: when it's colder, the positive phase maked the rainfall in Yangtze reach decrease;on the contrary, when it' warmer, the positive phase makes the rainfall in the south of China increase. Because of the SST in India Ocean getting warmer, the Walker circulation anomaly influences the Hadley circulation which influences rainfall over China further.