A Study On The Relationship Between The Asia-Pacific Oscillation And Autumn Precipitation In China

The autumn precipitation is unevenly distributed in China,with significant interannual and interdecadal changes,which can cause huge natural disasters because of the droughts and floods.In order to further understand the autumn precipitation in China and achieve the early warning capability for natural disasters,based on NCEP/NCAR reanalysis and observational data,the relationship between Asian-Pacific Oscillation(APO)and autumn precipitation in China from 1960 to 2016 was investigated by using statistical methods such as EOF,correlation,regression and composite.The research results show that:(1)Autumn APO(September ? October mean)has a significant positive correlation with the accumulated precipitation in central eastern China,with a correlation coefficient of 0.61.Further analysis revealed that when the APO is strong,the strengthened East Asian trough and the North Pacific high / vertical shear occur in the mid-lower / upper troposphere,resulting in anomalous southerly along the East Asia coast,which are favorable for strengthening the anomalous convergence and upward movement of moist warm air from the northwestern Pacific and arid cold air from the north China,introducing more(less)precipitation,but that this configuration became much diminished during weak APO years.It should be noted that the water vapor transmission anomalies caused by tropical circulation changes on autumn central east China precipitation plays an important role.During strong autumn APO years,strengthened walker circulation,convergence at lower troposphere and divergence upper troposphere over the western Pacific cause a strong vertical upward movement in and around the western Pacific Ocean.In addition,the vertical meridional circulation over northern hemisphere further indicates that the increase of water vapor and convergence upward movement can be extended to the central and eastern regions of China,which is conducive to precipitation.The possible physical mechanism for the close connection between the two is the decrease / increase of surface sea temperature anomaly in the eastern equatorial Pacific / the western equatorial Pacific and subtropical Pacific is beneficial for stimulating a strong APO teleconnection pattern,which further affects precipitation in CEC by strengthening the connection between tropical and subtropical regions.(2)Through the analysis of the influence of preceding APO on autumn precipitation in China,the study found that APO in August also had a significant positive correlation with the accumulated precipitation in autumn(September-October),with the correlation coefficient up to 0.47.Further analysis of the atmospheric circulation anomaly associated with August APO shows that the changes in atmospheric circulation are similar to autumn APO's results.During strong August APO years,the significant negative / positive SLP and 500 h Pa potential height anomalies are located in the Asian continent / the north Pacific Ocean,with the significant vertical shear of the east Asian jet at 200 h Pa.For the highly similarity of atmospheric circulation between August and autumn APO over Asia-Pacific region,the possible mechanism can be explained as the thermal effect in the mid-upper troposphere can last from August until autumn,and the corresponding simultaneous thermal effect would lead to anomalies in both atmospheric circulation and precipitation.In addition,the tropical Pacific SST in August(Ni?o4 index)can also better indicate the autumn precipitation in central eastern China,which shows the characteristics of alternating changes with august APO on the interdecadal relationship.However,the prediction results of autumn extreme precipitation in central eastern China show that APO is better than Ni?o4 index on the interannual scales.Therefore,APO can be considered as a new way and method to predict precipitation,which has great significance to predict autumn precipitation in China.