Motivating Mechanisms of the South Asian Jet Wave Train by Disturbances over the North Atlantic in Winter

Abstract This study investigated the motivation of the South Asian jet wave train (SAJW) and its underlying mechanism, by distinguishing different evolutions of disturbance sources over the North Atlantic. The disturbance sources propagate along the SAJW toward the western North Pacific in the propagating cases, while they are constrained over the North Atlantic and Europe in the interrupted cases. The possible motivating mechanisms are disclosed in the perspectives of energy dispersion and background potential vorticity gradient (PVG) affecting energy attraction. In the propagating cases, wave energy propagates eastward over the North Atlantic and converges into the Mediterranean Sea and Middle East, leading to the amplification and development of the wave train. The enhancement of PVG over south Europe–Mediterranean Sea is a key factor attracting such eastward propagation, which is associated with the positive PV anomaly over north Europe driven by the diabatic heating of precipitation. In the interrupted cases, energy dispersion is more divergent over the North Atlantic because of the weaker PVG, resulting in the failure of the SAJW excitement. The impacts of the SAJW on the temperature and precipitation along its path are evident, with the modulated snow depth agreeing more with temperature rather than precipitation except over the Tibetan Plateau. Hence, understanding the motivating mechanism of the SAJW is essential for improving weather forecasts over subtropical Eurasia by using the disturbances over the North Atlantic.