The Winter Concurrent Meridional Shift of the East Asian Jet Streams and the Associated Thermal Conditions

Abstract

Abstract In this study, the concurrent meridional shift of the East Asian polar-front jet (EAPJ) and the East Asian subtropical jet (EASJ) and the associated thermal conditions have been investigated. The concurrent meridional shift is dominantly characterized by an out-of-phase shift of the two jets, as an equatorward shift of the EAPJ and a poleward shift of the EASJ, and vice versa. This shift is linked with the dipole surface air temperature (SAT) anomaly over the Eurasian continent and a La Niña–like sea surface temperature (SST) anomaly. Associated with the dipole SAT anomaly, the meridional temperature gradient (MTG) anomaly exhibits a tripole pattern from low to high latitudes over the Eurasian continent, as well as an enhanced maximum eddy growth rate and an anomalous divergence of Eliassen–Palm flux (E-P flux) over the regions between the EAPJ and EASJ. Additionally, the synoptic-scale transient eddy activities (STEA) significantly decrease over the high latitudes and enhance between the EAPJ and EASJ. All the anomalies would benefit the equatorward and poleward shift of the EAPJ and EASJ, respectively. The MTG, E-P flux and STEA anomalies are also indicated in that associated with the Niña-like SST anomaly. Particularly, the variations are evident in low latitudes. The pathway of the stationary Rossby wave activity flux anomalies shows an eastward Rossby wave packet propagation along the southern portion of the EAPJ is associated with the SAT anomaly and that along the northern portion of the EASJ is associated with the SST anomaly. The relative contributions of the two thermal conditions have emphasized the role of the dipole SAT anomaly, based on multilinear regression.