2015年夏季东亚和南亚降水异常与热带太平洋海温异常的联系及机理

2015年我国东部夏季降水呈现南北反位相的空间分布,河套地区降水异常偏少、长江中下游地区降水异常偏多,同期印度中部地区降水负异常,上述三个区域2015年夏季降水距平百分率绝对值极大值均超过55%。东亚和南亚地区2015年夏季降水异常的形成机理主要是由于该年夏季处于El Niňo事件的发展位相,菲律宾群岛及邻近区域反气旋环流异常,江淮地区至日本列岛气旋式环流异常,对流层低层位势高度异常场和整层水汽异常输送场亦存在相一致的空间分布,表现为负位相的EAP(East Asian-Pacific)/PJ(Pacific-Japan)型遥相关,有利于河套地区降水偏少和长江流域降水偏多。热带太平洋海温异常引起热带地区Walker环流负异常,热带西太平洋地区上空受异常下沉气流控制,热带印度洋区域对流层盛行东风异常,减弱了印度夏季风,并造成了印度中部地区夏季降水偏少。另一方面,印度上空对流层低层受异常反气旋控制,该异常反气旋北侧的西风异常沿着青藏高原南麓向东运动,增强了与EAP/PJ型遥相关相联系的异常水汽输送,有利于维持和增强河套地区降水负异常和长江中下游地区降水正异常。

Relationship of East and South Asia summer precipitation anomalies with tropical Pacific SSTA in 2015 and its mechanisms

The spatial distribution of summer precipitation in eastern China in 2015 shows a reverse phase relationship between north (Hetao area,HT) and south (the middle and lower reaches of Yangtze River Valley,YRV).The precipitation anomalies in HT and central India (CI) are below-normal,while those are above-normal in YRV.The absolute maximum of summer precipitation anomaly percentage in the above three areas in 2015 is more than 55%.The formation mechanism of precipitation anomalies in East and South Asia during boreal summer of 2015 is mainly due to the development phase of El Niño event at the same time.An anticyclone circulation anomaly in the Philippine Islands and its adjacent regions,a cyclone circulation anomaly in the Yangtze-Huaihe region to the Japanese archipelago,and the geopotential height anomaly field in the lower troposphere and the water vapor transport anomaly field in the whole troposphere also have the same spatial distribution,which also reveals the spatial distribution of negative EAP (East Asian-Pacific)/PJ (Pacific-Japan) teleconnection.It is beneficial to less precipitation in HT and more precipitation in YRV.The tropical Pacific SSTA weakens the Walker circulation in the tropical region,which contributes to the descending motion over the western tropical Pacific.The abnormal tropospheric easterly prevails in the tropical Indian Ocean,which weakens the Indian summer monsoon and results in below-normal precipitation in CI during boreal summer.Meanwhile,the lower troposphere over India is controlled by an anomalous anticyclone.The westerly anomaly on the northern side of the anomalous anticyclone moves eastward along the southern edge of the Tibetan Plateau,which enhances the anomalous water vapor transport associated with EAP/PJ teleconnection.Therefore,it is conducive to maintaining and strengthening the below-normal precipitation in HT and the above-normal precipitation in YRV.