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

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.