Quantifying the dynamics of the interannual variabilities of the wintertime East Asian Jet Core

Abstract

The East Asian jet has evident interannual variability in strength and position and has broad impacts on weather and climate in the Asian-Pacific-American region. In this study, we quantify the relative contributions of distinct dynamical processes responsible for the wintertime interannual variability of the East Asian jet core. The quantification is based on analyzing the zonal momentum budgets. Our budget analyses show distinct up- and downstream controls for the interannual intensification of the jet. Over the upstream, the jet intensification is predominantly driven by enhanced upper-level angular momentum transport associated with local convective-driven Hadley-cells. In addition to convections over the Tropical Pacific, those over the Bay of Bengal–South China Sea are found responsible for a distinct local Hadley cell over 80∘–100∘ E, which accelerates the jet from its very upstream. Over the downstream, angular momentum advected by the mean flow from the upstream is the first-order term responsible for the jet intensification, whereas synoptic eddies play a secondary role. For the interannual meridional displacement of the jet, synoptic eddy activities over the North Pacific are found to contribute predominantly. For both the intensification and the meridional displacement, the upper-tropospheric jet covaries closely with changes in the Subtropical Oceanic Frontal Zone in the North Pacific. Such a strong covariation implies the contributions of the air–sea interactions to the downstream jet variability.