Different configurations of the Eurasian pattern and South Asian jet wave train and their impacts on the winter climate over East Asia

Wave trains propagating across Eurasia at both high and low latitudes in winter are key to the climate variation over East Asia via modulating the cold surge and moisture supply, with different configurations inducing diverse impacts. In this study, the combined impacts of the Eurasian (EU) pattern and South Asian jet wave train (SAJW) at a 10-30-day timescale are compared when they work in phase (indices of same signs) and out of phase (indices of opposite signs). Different configuration is defined by considering whether they induce a concurrent or reversing center of action over East Asia-Japan. The in-phase configuration induces a strong outbreak of the East Asian winter monsoon by intensifying the East Asian trough. In contrast, the out-of-phase configuration restricts the cold air over North China and enhances the moisture supply from the low latitudes by intensifying the India-Burma (now Myanmar) trough and an anomalous anticyclone over East Asia-the western North Pacific, inducing abnormal precipitation over Southwest and North China. In in-phase configuration, the EU pattern and SAJW are excited by abnormal disturbances over the western North Atlantic. The disturbance energy splits over Europe and joins over East Asia, intensifying the East Asian trough concurrently. In out-of-phase configuration, the two teleconnections do not share a common upstream source; they develop individually over the eastern North Atlantic in high and subtropical latitudes. They join north of the Bay of Bengal, resulting in a deepened India-Burma trough and an onward western North Pacific anticyclone anomaly. Both the EU pattern and SAJW influence the East Asian trough and the India-Burma trough in different configurations mainly via the advection of abnormal vorticity along wave trains by the subtropical westerly jet stream, with the anticyclonic Rossby wave source and Beta effect playing a negative role.