The relationship between the Asian-Pacific Oscillation and January precipitation anomalies over southern China

Using the NCEP,ERA-40 rcanalysis datasets and the monthly precipitation data from the 160 stations of China, the relationship between the January precipitation anomaly over southern China and the simultaneous Asian-Pacific Oscillation (APO),as well as the previous APO, is investigated,and the associated mechanism for the relationship is also discussed.The results show that the January APO index can reflect well the simultaneously anomalous precipitation over southern China.The variability of APO may lead to the anomalous gcopotential height at the lower troposphere and be then closely related to the anomalous precipitation over southern China through affecting the lower-tropospheric winds at the lower latitudes.Corresponding to lower (higher) APO index, the lower-tropospheric gcopotential height is higher (lower) over the southern part of East Asia and its adjacent oceans and is lower(higher) over the eastern Pacific.Accordingly, the southwesterly(northeasterly) winds prevail over the South China Sea and the coast of South China, and they gradually weaken from the South China Sea to southern China, which result in a convergence (divergence) over southern China.Consequently, the southwesterly (northcasterly) winds may lead to more (less) warm and humid air transportation into southern China and the associated vapor convergenec (divergence),and eventually give rise to more(less) precipitation over southern China.The APO has a good persistenec.Specifically, the anomalous signal of the October APO can persist until the following January, accompanying with continuous high corrclations between the October APO index and that in the following months until January.Therefore, the previous October APO index has a significant relationship with the following January precipitation over southern China, and can be considered as an important precursory factor.