冬季北太平洋风暴轴和北大西洋风暴轴的协同变化及其与同期海气系统的空间耦合关系

Concurrent Variations of Northern Atlantic and Pacific Storm Tracks and Their Relationship to the Coupled Pattern of Atmosphere–Ocean System during Winter

基于1960~2014年NCEP/NCAR(美国环境预报中心和国家大气研究中心)的逐日再分析资料以及NCPC(美国气候预报中心)的海温资料和大气环流及海洋指数,通过风暴轴指数、经验证交分解(EOF)等方法,研究了冬季北半球北太平洋风暴轴(PST)和北大西洋风暴轴(AST)之间不同时间尺度下的协同变化特征,并利用回归和相关分析对风暴轴的年际和年代际协同变化特征与同期海气系统的空间耦合关系进行了探讨。主要结论概括如下:(1)从所定义的冬季北半球两大洋风暴轴的纬度、经度和强度指数来看:三个指数均存在明显的年际变化和年代际变化,其中年际分量的方差贡献远大于年代际分量;对于单个风暴轴来讲,无论是滤波方差场原始序列还是其年际分量和年代际分量序列,每个风暴轴各自的纬度指数和经度指数均呈显著正相关,表明每个风暴轴各自的南北位移和东西位移具有很好的协同性;虽然从原始序列来看,两个风暴轴之间各指数之间的相关关系均并不显著,但是对于年际分量序列和年代际分量序列,两个风暴轴之间均具有显著的协同性变化,其中,在年际尺度上,两者仅强度变化之间具有显著的正相关,而在年代际尺度上,AST的经度(纬度)变化与PST的强度(纬度及强度)变化均具有显著的负相关。(2)EOF结果表明,两个风暴轴之间协同变化的空间结构在年际尺度上反映的主要是强度的变化,第一模态为两者强度在其气候平均位置附近同时减弱(增强)并伴随AST整体和PST东部均略有北抬(南压),第二模态为两者强度在其气候平均位置附近同时减弱(增强)并仅伴随AST整体略有南压(北抬);而在年代际尺度上,第一模态为AST整体偏北(南)中东部偏强(弱)与PST整体偏南(北)中东部偏弱(强)的反位相协同变化;第二模态为两个风暴轴的强度在其气候平均位置附近同时增强(减弱)的一致性协同变化。(3)进一步分析表明,两个风暴轴之间以不同模态协同变化时,与同期海温、遥相关型及环流异常等海气系统之间均呈现出很好的空间耦合关系,但具有不同的特点。

Using daily analysis data of the NCEP/NCAR（National Centers for Environmental Prediction/National Center for Atmospheric Research）, monthly SST（sea surface temperature）, and climate indices of atmosphere and ocean time series from the NCPC（National Climate Prediction Center） from 1960 to 2014, characteristics of concurrent variations of the northern Atlantic storm track（AST） and Pacific storm track（PST） at various time scales in boreal winter are analyzed based on calculations of the storm track indices and EOF（empirical orthogonal function） analysis. The simultaneous coupled patterns of the concurrent variations of the storm tracks and their relation to the atmosphere–ocean system are also studied on interannual and interdecadal scales using regression and correlation analysis methods. The results are summarized as follows.（1） In terms of the defined latitude, longitude, and intensity indices of the storm tracks, there exist significant interannual and interdecadal variations in the above three indices, and the variance contribution of the interannual component is much larger than that of the interdecadal component. As for each single storm track in its original or interannual and interdecadal series, there is a significant positive correlation between its latitude and longitude indices, which indicates that the variation of meridional and zonal position displacements is synchronous. Although none of the concurrent correlations between the AST and PST indices has past the significance test in the original series, there are significant concurrent variations between the storm tracks in the interannual and interdecadal series, e.g., on the interannual scale, the two storm tracks show a significant positive correlation only in their intensity indices. However, on the interdecadal scale, there is a significant negative correlation between the longitude（latitude） index of AST and the intensity（latitude and intensity） index of PST.（2） The EOF result shows that the spatial structure of the concurrent variations between the two storm tracks in boreal winter mainly reflects the intensity variation on the interannual scale. The first mode describes the two storm tracks weakening（intensifying） synchronously at their respective climatological positions with a slight northward（southward） shift of the whole AST and eastern PST. The second mode describes their synchronous weakening（intensifying） at their respective climatological positions with a slight southward（northward） shift of the whole AST. While on the interdecadal scale, the first mode reveals an out of phase variation between AST and PST, i.e., a northward（southward） shift of the whole AST as well as intensifying（weakening） in its middle–eastern part correspond to a southward（northward） shift of the whole PST as well as weakening（intensifying） in its middle–eastern part. The second mode reveals a synchronous enhanced（reduced） variation in intensity between AST and PST at their climatological positions.（3） Further analysis shows that the different concurrent variations of the storm tracks are closely related to different simultaneous coupled patterns in SST, teleconnection and atmospheric circulation fields, etc. within the atmosphere–ocean system.