阿留申低压与东亚冬季风关系的年代际变化

Interdecadal variations of the relationship between the Aleutian low and East Asian winter monsoon

东亚冬季风系统是北半球冬季最活跃的环流系统,通过与西伯利亚高压、阿留申低压、东亚大槽和东亚西风急流等系统之间的相互作用,对东亚地区的气候产生重要影响。本文主要关注阿留申低压与东亚冬季风关系的年代际变化特征,利用经验正交函数分析方法,提取阿留申低压的强度变化、南北移动、西北-东南传播型和东西移动模态,并研究这4种模态与冬季风的北部型、南部型模态关系。结果表明阿留申低压的强度变化与2种东亚冬季风型的关系都不显著。阿留申低压的南北移动与南部型冬季风的相关性较强且具有年代际变化特征。1995年后南北涛动中心受ENSO(El Ni1o-Southern Oscillation)影响向东移动,阿留申低压和西伯利亚高压的配置不利于中国东南部气压梯度的形成,导致阿留申低压的南北移动与南部型冬季风的相关性降低。另外,1975年后北大西洋涛动在中西伯利亚地区激发正位势高度异常,扩大传播型模态影响范围,给中高纬地区带来东北风异常,有利于北部型冬季风的形成,此时传播型模态与北部型冬季风显著相关。东亚冬季风系统是北半球冬季最活跃的环流系统,通过与西伯利亚高压、阿留申低压、东亚大槽和东亚西风急流等系统之间的相互作用,对东亚地区的气候产生重要影响。本文主要关注阿留申低压与东亚冬季风关系的年代际变化特征,利用经验正交函数分析方法,提取阿留申低压的强度变化、南北移动、西北-东南传播型和东西移动模态,并研究这4种模态与冬季风的北部型、南部型模态关系。结果表明阿留申低压的强度变化与2种东亚冬季风型的关系都不显著。阿留申低压的南北移动与南部型冬季风的相关性较强且具有年代际变化特征。1995年后南北涛动中心受ENSO(El NinoSouthern Oscillation)影响向东移动,阿留申低压和西伯利亚高压的配置不利于中国东南部气压梯度的形成,导致阿留申低压的南北移动与南部型冬季风的相关性降低。另外,1975年后北大西洋涛动在中西伯利亚地区激发正位势高度异常,扩大传播型模态影响范围,给中高纬地区带来东北风异常,有利于北部型冬季风的形成,此时传播型模态与北部型冬季风显著相关。

The East Asian winter monsoon(EAWM)system is one of the most active circulation systems during winter in the Northern Hemisphere.It exerts a major impact on the near-surface temperature and precipitation in East Asia through interactions with the Siberian high,Aleutian low(AL),East Asian trough,and East Asian westerly jet stream.Despite the importance of the relationship between the AL and East Asian winter monsoon,there have been relatively few studies on it and its variations.In this study,an EOF analysis is performed to analyze the intensity change,north-south and east-west movement,and Northwest-Southeast propagation modes of the AL,and to depict the relationships among these four modes and the northern and southern patterns of the EAWM.The EOF analysis is also used to extract the main modes of near-surface temperature.The explanatory variance of the first mode is 48.9%,which shows that the near-surface temperature is uniformly distributed throughout the country,and that the temperature decreases rapidly to the north along the meridional gradient.This pattern is called the northern EAWM mode.The second mode accounts for 16.2%of the total variance,showing a reverse distribution from north to south,which is called the southern EAWM monsoon.The results show that,although the intensity variation of the AL and the two East Asian winter monsoon modes are insignificant,the meridional movement of the AL is strongly correlated with the southern EAWM mode,with a feature of decadal variation.Considering that the interdecadal variation of AL and EAWM will affect their correlative features,the time series of the four modes and two types of winter monsoon are studied by 21-point sliding correlation.From 1964 to 1994,there was a significant positive correlation between the north-south movement of the AL and the southern EAWM mode.After 1994,the axis position of the north-south oscillation over the North Pacific moved eastward under the influence of ENSO,and the configurations of the AL and Siberian high have not been conducive to the formation of the pressure gradient in southeastern China.In this study,we take 1978 as a typical case of southern EAWM mode,and obtain the distribution patterns of the north-south movement AL and southern winter monsoon.The Northwest-Southeast propagation mode is strongly correlated with the northern EAWM pattern,and the decadal change of this relationship is mainly affected by the North Atlantic Oscillation.There is no significant correlation between the propagation mode and northern EAWM monsoon during the period of 1961—1974.After 1974,the North Atlantic Oscillation stimulates anomalous positive potential height anomalies in the central Siberian region,expands the influence extent of the Northwest-Southeast propagation mode,and brings northeasterly anomalies to the middle and higher latitudes.We also take 1976 as a case study of northern EAWM monsoon,and the study results are consistent with our predictions.In this paper,the relationship between the intensity change and east-west movement of AL pressure and their winter winds is not very significant,thus we have not carried out further analysis on this issue.In future research,we will continue to focus on the influence of four-mode interannual changes in the AL on winter monsoon,so as to supplement the results of this paper.