Connections between wintertime jet stream variability, oceanic surface heating, and transient eddy activity in the North Pacific

摘要

A set of statistical analyses of the fields from the European Center for Medium-Range Weather Forecasts reanalysis (ERA-40) are carried out to investigate the connections between three selected fields, namely, the wintertime western Pacific jet stream (WPJS), as represented by the zonal wind at 200 hPa; the oceanic surface heating represented by the latent and sensible heat fluxes; and the synoptic-scale transient eddy activity (STEA) over the North Pacific. First, empirical orthogonal function (EOF) analysis is performed to characterize the wintertime WPJS variability. Further analyses yield the following conclusions. (1) The most dominant relationship among the three selected fields is strongly linked to the El Ni?o-Southern Oscillation (ENSO). During ENSO events, anomalous zonal wind at 200 hPa downstream of the WPJS main body, shown in the first EOF, is accompanied by STEA anomalies around the region of the anomalous midlatitude zonal wind. (2) The strengthening (weakening) of the wintertime WPJS main body, shown in the second EOF, is connected to the surface heating anomalies in the Kuroshio and its extension region as well as to STEA anomalies in the region downstream of the WPJS main body. (3) The northward (southward) shift of the wintertime WPJS, represented in the third EOF, is closely related to the south-north dipolar structure of the surface heating anomalies in the western North Pacific. The STEA spatial displacement is in conjunction with the shift of the jet stream in the same direction due to the dynamical connection between the winds and the eddies. Furthermore, the STEA anomalies in winter may cause the WPJS anomalies on the submonthly timescale. As a consequence, the northward (southward) shift of the STEA is harmoniously in favor of the similar jet shift.