Impact of East Asian winter monsoon on the Pacific storm track

Abstract

The storm track plays an important role in modulating the variability of atmosphere circulations such as day-to-day weather variability and teleconnection patterns. The variation in amplitude of the storm track is usually related to the midlatitude basic flow. Recent studies show that a strong (weak) East Asian winter monsoon (EAWM) and weak (strong) synoptic eddy activity lead to the weakening (enhancement) of the Pacific storm track. Two empirical orthogonal function (EOF) modes of the EAWM were identified recently. However, their different impacts on the position and intensity of the Pacific storm track are not clear. Based on the ECMWF 40Year Re-analysis (ERA40) data, the different responses of the Pacific storm track to these two EOF modes of EAWM are investigated in this study. The results imply that the first EOF mode (i.e., the northern mode) of EAWM, characterized by a northward-shifted westerly jet tends to lead to a northward shift of the Pacific storm track. The second EOF mode (i.e., the southern mode) of EAWM, featured by a more southward located westerly jet stream, tends to cause a southward shift of the Pacific storm track. Moreover, the amplitude of the Pacific storm track associated with the southern mode is considerably weaker than the amplitude associated with the northern mode. It is also demonstrated that the westerly jet associated with the EAWM may play an important role in transporting the upstream synoptic waves to the Pacific Ocean and contributing to the development of the Pacific storm track.