与印度洋偶极子模态有关的西太平洋海温异常型及其对东亚冬季气候的影响

Winter SST Variation Patterns in the Subtropical Western Pacific Associated with Indian Ocean Dipole and Their Influences on East Asian Winter Climate

利用NOAA(National Oceanic and Atmospheric Administration)海温、GPCP(Global Precipitation Climatology Project)降水和ERA-20C(ECMWF's first atmospheric reanalysis of the 20th century)再分析大气环流资料,结合大气环流模式ECHAM5敏感性试验,研究了与秋季印度洋海温偶极子模态(IOD)相联系的冬季热带西太平洋海温异常型及其对东亚冬季气候的影响。发现在秋季发生IOD背景下,冬季西太平洋存在两类海温异常的变化型:一类是西太平洋区域一致偏暖/冷的模态,另一类是区域西冷东暖/西暖东冷的模态。尽管西太平洋海温一致偏暖和西冷东暖这两类海温变化型均有利于华南冬季少降水,但影响的范围有所不同。一致偏暖型引起的少降水范围较大,从华南扩展到长江中下游地区。西冷东暖型引起少降水范围主要限于华南,而在长江中下游到华北则降水偏多。相应地,在大气环流上,尽管两类海温异常型均有利于在西北太平洋菲律宾海附近出现气旋式环流异常,但气旋的强度和中心位置有差异。一致偏暖型引起的气旋偏强,中心位置偏西,其后部异常东北风控制的范围更大,导致少降水范围更大,而西冷东暖型引起的气旋偏弱,中心位置偏东,其后部异常东北风控制的范围小,导致少降水区域主要在华南沿海。本文结果对认识IOD调制随后冬季东亚降水异常的机理有重要意义。

Using NOAA(National Oceanic and Atmospheric Administration)observational SST(Sea Surface Temperature),GPCP(Global Precipitation Climatology Project)precipitation,and atmospheric circulation variables from the ERA-20C(ECMWF's first atmospheric reanalysis of the 20th century)reanalysis,winter SST variation patterns in the tropical western Pacific,which are related to the tropical Indian Ocean SST Dipole(IOD),and their impacts on East Asian climate are studied.Two types of SSTA(SST anormaly)pattern are found:A regional unanimous warm/cold pattern and a dipolar mode with SST anomalies in the western side opposite to that in the eastern side of the region.The two types of SSTA pattern both are favorable for winter precipitation suppression in southeastern China,but the domain sizes affected are different.The unanimous SSTA pattern affects a larger region from South China to the middle and lower reaches of Yangtze River.The impact of the SSTA dipole pattern is only confined to South China,leading to less rainfall in South China but more rainfall in the middle and lower reaches of Yangtze River.The corresponding atmospheric circulation anomalies can explain these rainfall anomalies.Although an anomalous cyclone occurs over the Philippine Sea in both of the cases,its strength and location are different.The cyclone forced by the unanimous warm SST pattern is stronger,and thus the anomalous westerly and northeasterly in the rear extend to a wider region,leading to a dry condition in a larger domain.In contrast,the cyclone forced by the dipolar pattern is weaker and the anomalous easterly and northeasterly are confined to a smaller area,leading to a dry condition only in southern China.Sensitive experiments by an AGCM,i.e.,ECHAM5,validate the above results.