The Linkage between Upper-Level Jet Streams over East Asia and East Asian Winter Monsoon Variability

Abstract

This study investigates the linkage between East Asian winter monsoon (EAWM) variability and upper-level jets, with particular focus on the East Asian polar front jet (PJ) and its concurrent variation with the subtropical jet located to the south of the Tibetan Plateau (TSJ). The winter upper-level zonal wind variations over the Asian landmass (70°–120°E) are dominated by two principal modes (i.e., meridional displacement of the PJ and out-of-phase variation in the intensity of the TSJ and PJ) and they are closely linked to the EAWM northern mode and southern mode, respectively. Southward shifting of the PJ concurs with northwestward displacement of the Siberian high (SH), an enhanced northern East Asian trough, leading to cold winter in northern East Asia. Meanwhile the simultaneous TSJ intensification and PJ weakening is linked to an amplified SH, a southward shift of the Aleutian low (AL), a strengthened southern East Asian trough, and a wavelike anomaly pattern extending from western Barents Sea downstream to East Asia at the 500-hPa level. Equatorward shift of the PJ is associated with La Niña conditions in the tropics and sea ice anomalies over the Arctic. An intensified TSJ and weakened PJ are preceded by autumn warming over the central and eastern Pacific Ocean and are linked to circulation anomalies induced by the extensions of stationary Rossby waves, as well as synoptic-scale transient eddy activity anomalies. Therefore, a combination of external forcing and internal atmospheric dynamics plays a role in driving the variations of two leading EOFs, and there is potential for seasonal forecasting of both modes.

Anthropogenic aerosol effects on East Asian winter monsoon: The role of black carbon‐induced Tibetan Plateau warming

“…In previous studies, the strengthening of the EAWM northern mode is found to be correlated to the diminished sea ice of Arctic regions [ Luo and Zhang, ; Inoue et al, ] in recent decades. A decrease of the sea ice (warming in Arctic) tends to weaken the baroclinicity in subarctic areas and favors the cold air outbreak in northern Siberia.…”

“…Our model results suggest that the BC‐induced TP warming can be an alternative mechanism responsible for the strengthening of the EAWM northern mode. Recent observational studies have detected both the TP warming trend [ Duan and Xiao , ] and the intensification of the EAWM northern mode in recent decades [ Luo and Zhang, ]. These observation facts provide a support for the dynamical relationship between the TP warming and the intensification of EWAM northern mode, as identified from this study.…”

“…The relationship between these two modes and the EAWM circulation is also noticed. The northern mode is associated with the westward shift of the East Asian major trough and with the northward shift of subtropical jet stream [ Luo and Zhang , ]. The southern mode, however, is associated with a typical stronger EAWM, which is characterized by the deepening East Asian major trough and the strengthening of subtropical jet stream.…”

A Model Investigation of Aerosol‐Induced Changes in the East Asian Winter Monsoon

“…To the northern flank of the subtropical jet, the East Asian trough remarkably deepens, characterized by an elongated belt with negative 500‐hPa geopotential height anomalies extending from central Asia to the central Pacific (Figure c). The mid‐upper tropospheric circulation anomalies favor the occurrence of cold air intrusions and, thus, an intensified EAWM circulation (Chen et al, ; Luo & Zhang, ; Zhang et al, ).…”

Variability in zonal location of winter East Asian jet stream

“…Previous studies have shown that the winter EAJS is associated with many synoptic-scale phenomena such as cyclogenesis, frontogenesis, blocking, storm track activity, severe snow storm, and freezing rain (Palmén and Newton, 1969;Zeng, 1979;Kung and Chan, 1981;Dole and Black, 1990;Gao and Tao, 1991;Mao et al, 2007;Liao and Zhang, 2013;Zhang and Zhang, 2013). Much effort has been devoted to the study of the intensity variability of the EAJS and its association with the East Asian winter monsoon (EAWM) in seasonal and long timescales (Yang et al, 2002;Jhun and Lee, 2004;Ding, 2005;Li and Yang, 2010;Zhang and Huang, 2011;Luo and Zhang, 2015).…”