Concurrent variations in the location and intensity of the Asian winter jet streams and the possible mechanism

Abstract

This study investigates the concurrent variations in the location and intensity of the East Asian subtropical jet (EASJ) and polar front jet (EAPJ) with a focus on the relationship between the variations and the atmospheric circulation in the mid-latitude region. The possible mechanisms for the concurrent variations of the EASJ and EAPJ are explored. The wintertime upper-level zonal wind variation over the landmass (50°–100°E) is characterized by two principal modes, i.e., the out-of-phase variations in the intensity and the meridional displacements of the EASJ/EAPJ. The EASJ and EAPJ are intensified (weakened) when they are located close to (far away from) each other, corresponding to a weakened (intensified) East Asian trough over the northern Pacific region and a decreased (increased) geopotential height in the mid-latitude over central Asia. The spatial pattern of 500 hPa geopotential height anomaly is similar to the Eurasian teleconnection pattern, while the pattern of sea level pressure anomaly shows a feature similar to the Arctic oscillation. Analyses of related thermal-dynamical processes indicate that the increased (decreased) diabatic heating and horizontal heat transport lead to a larger (smaller) meridional temperature gradient over the EASJ/EAPJ regions, which subsequently intensifies (weakens) the East Asian jets. Severe (weak) convective activities accompanied with warmer (colder) SST in the tropics also contribute to the intensification (weakening) of the EASJ and EAPJ. Dynamically, the strong (weak) divergence of the eddy vorticity flux along the northern Tibetan Plateau and that of the Eliassen–Palm flux of the synoptic-scale stationary waves are favorable for the intensification (weakening) of zonal winds through the wave-mean flow interactions. As a result, the EASJ and EAPJ are intensified (weakened).