IPO调节大西洋纬向模对澳大利亚秋季降水年际变动的影响

采用1900—2014年115 a的观测和再分析资料,使用滤波、线性相关等方法,研究太平洋年代际振荡(Interdecadal Pacific Oscillation,IPO)调节大西洋纬向模(Atlantic Zonal Mode,AZM)对澳大利亚秋季降水年际变动的调节作用及机制。结果表明,当IPO位于正位相时,AZM引起澳大利亚中部秋季降水减少;而当IPO位于负位相时,AZM引起澳大利亚中南部秋季降水增加。这是因为在IPO正位相年,AZM引起的热带大西洋异常上升运动的下沉支主要位于热带东太平洋,并通过调节热带太平洋的沃克环流引起海洋性大陆的异常上升运动。该异常上升运动调节了局地哈得来环流,在澳大利亚中部引起异常下沉,结合对流层低层的反气旋异常风场,不利于澳大利亚中部的对流发展和热带印度洋的暖湿水汽输送,导致澳大利亚中部出现大面积降水减少。而在IPO负位相年,由于气候基本态的不同,AZM的振幅比IPO正位相年高近四分之一,并且AZM引起的南半球中高纬地区Rossby波在澳大利亚及其西部地区引发正压性气旋异常。该气旋异常不仅引起澳大利亚地区的异常上升运动,同时对流层低层的气旋性环流异常引导更多热带印度洋暖湿气流进入中南部澳大利亚,导致此地区降水增加。本研究的结果表明IPO可通过改变气候基本态,调节AZM模态的强度及其遥相关。

IPO modulates the influences of Atlantic Zonal Mode on the interannual variations of Australian autumn precipitation

Using the observation and reanalysis data for the period of 1900-2014,this study shows that the impacts of Atlantic Zonal Mode (AZM) on the interannual variations of Australian autumn precipitation can be modulated by Interdecadal Pacific Oscillation (IPO).It is revealed that,when the IPO is in the positive phase,the AZM decreases the autumn precipitation in central Australia,whereas,when the IPO is in the negative phase,the AZM increases the autumn precipitation in central and southern Australia.The reason for this is that,during the IPO positive phase,the anomalous warming and ascending motion in the tropical Atlantic related to the AZM induce anomalous descending motion over the tropical eastern Pacific,thereby leading to anomalous upward motion around the Maritime continent.The anomalous upward motion adjusts the local Hadley circulation and results in anomalous subsidence in central Australia.This,together with the anomalous anticyclone in the lower troposphere,the southeasterly anomalies of which along the northwestern frame hinder the transport of warm and humid water vapor from the tropical Indian Ocean,results in a precipitation deficit in central Australia.In contrast,during the IPO negative phase,due to the different basic state and stronger AZM amplitude when compared to those during the IPO positive phase,the Rossby wave in the mid-high latitudes of the Southern Hemisphere caused by the AZM induces a barotropic cyclone in Australia.The anomalous cyclone not only trigger the anomalous ascending motion,but also contribute to the greater transportation of warm moisture from the tropical Indian Ocean to central and southern Australia,by means of the anomalous northwester lies along the northwestern frame,in turn leading to surplus precipitation in this region.Therefore,the IPO modulates the AZM-Australian precipitation relationship by altering the basic state and AZM amplitude.