Group seminar on 02. November, 14:15 CET
On the seasonal and intraseasoanl variations of the Pacific Storm track during the cool season
Yuan-Bing Zhao
Previous studies found that the Pacific storm track intensity during the cool season is negatively correlated with the upper-tropospheric jet strength, contradicting the traditional linear theory of baroclinic instability. In the seasonal march, such a variation manifests itself as the midwinter suppression of the storm track intensity, while in the intraseasonal variation the storm track intensity in winter months is found to be unexpectedly weak when the Pacific jet is extremely strong.
Using a functional analysis apparatus, multiscale window transform (MWT), and the MWT-based localized multiscale energetics analysis, the underlying mechanisms of these two counterintuitive variations were investigated, based on ERA-40 data from ECMWF. It was found that these two variations, which seem to be of the same dynamical origin, actually are different. The midwinter suppression results from a variety of different physical processes, including the weakening of downscale baroclinic(potential) energy transfer (compared to late fall), diabatic generation and upstream seeding, and also the strengthening of the frictional dissipation in midwinter, whereas the intraseasonal variation is mainly attributed to the extraordinarily strong upscale barotropic(kinetic) energy transfer in winter months of strong jet, which plays a role that is opposite to that in the formation of midwinter suppression.