The COWL Pattern Identified with a Large AO Index and Its Impact on Annular Surface Temperature Anomalies  

作　　者：施宁 布和朝鲁 

机构地区：[1]Key Laboratory of Meteorological Disaster of Ministry of Education,Nanjing University of Information Science&Technology [2]Nansen-Zhu International Research Centre,Institute of Atmospheric Physics,Chinese Academy of Sciences [3]Climate Change Research Center,Chinese Academy of Sciences [4]International Center for Climate and Environment Sciences,Institute of Atmospheric Physics,Chinese Academy of Sciences

出　　处：《Acta meteorologica Sinica》2012年第4期410-419,共10页

基　　金：Supported by the National Basic Research and Development(973)Program of China(2009CB421406);National Science and Technology Support Program of China(2009BAC51B02);National Natural Science Foundation of China(40975033)

摘　　要：In this study, the cold ocean/warm land （COWL） pattern was identified from the leading empirical orthogonal function （EOF） of the monthly 1000-hPa geopotential height field poleward of 20°N. Traditionally, the leading EOF has been recognized as the Arctic Oscillation （AO）, or Northern Annular Mode （NAM）, which causes annular surface air temperature （SAT） anomalies over high-latitude regions of the Northern Hemisphere. A new finding of the present study is that the total AO events defined by the large AO index actually include a distinct type of events that are characterized by a less-annular spatial structure, i.e., the COWL pattern, which shows an NAO-like distribution in the Atlantic sector and a center of action over the North Pacific with the same sign as that over the Arctic. In addition, unlike canonical AO events, the COWL events also show a less-annular pattern in the stratosphere. Statistically, at least one-third of the AO events can be categorized as the COWL events. The SAT anomalies associated with the COWL pattern have an annular distribution over the high-latitude region of the two continents in the Northern Hemisphere. In contrast, if the COWL events are removed from the total AO events, the remainder shows less annular SAT anomalies. Thus, the typical annular SAT anomalies associated with AO events are in large part due to the contribution of the COWL pattern. Furthermore, the monthly variability and the interannual variability of all the AO events are equally important.In this study, the cold ocean/warm land （COWL） pattern was identified from the leading empirical orthogonal function （EOF） of the monthly 1000-hPa geopotential height field poleward of 20°N. Traditionally, the leading EOF has been recognized as the Arctic Oscillation （AO）, or Northern Annular Mode （NAM）, which causes annular surface air temperature （SAT） anomalies over high-latitude regions of the Northern Hemisphere. A new finding of the present study is that the total AO events defined by the large AO index actually include a distinct type of events that are characterized by a less-annular spatial structure, i.e., the COWL pattern, which shows an NAO-like distribution in the Atlantic sector and a center of action over the North Pacific with the same sign as that over the Arctic. In addition, unlike canonical AO events, the COWL events also show a less-annular pattern in the stratosphere. Statistically, at least one-third of the AO events can be categorized as the COWL events. The SAT anomalies associated with the COWL pattern have an annular distribution over the high-latitude region of the two continents in the Northern Hemisphere. In contrast, if the COWL events are removed from the total AO events, the remainder shows less annular SAT anomalies. Thus, the typical annular SAT anomalies associated with AO events are in large part due to the contribution of the COWL pattern. Furthermore, the monthly variability and the interannual variability of all the AO events are equally important.

关 键 词：Arctic Oscillation spatial pattern COWL annular SAT anomalies 

分 类 号：P423[天文地球—大气科学及气象学]