Possible Influence Of The Variation Of Northern Atlantic Storm Track On The Activity Of China Cold Wave During Winter

On the basis of the daily mean temperature data over 566 stations from National Meteorological Information Center and reanalysis data of the US National Center for Environmental Prediction and the Center for Atmospheric Research (NCEP/NCAR), an analysis is conducted on the spatial-temporal evolution of the cold wave frequency of China (CCWF) and the north Atlantic storm track (NAST) during 50 winters through 1961/1962 to 2010/2011. The influence of NAST on CCWF and its possible mechanism are further discussed. Results are summarized as follows:(1) The result of singular value decomposition analysis (SVD) shows that, on the annual timescale, the position of NAST is closely linked to the cold wave frequency of China in winter, when the NAST moves northeastward (southwestward), the cold wave frequency in most stations decreases (increases) significantly, but the correlation between the intensity of NAST and the cold wave frequency of China is low.(2) There are two ways for the influence of the anomaly of NAST position on CCWF, on the one hand, the change of NAST position may lead to anomalous propagation of the synoptic-scale transient eddy activity (STEA),which could affects the CCWF directly; on the other hand, anomalous STEA could impact the general circulation firstly by feedback effect and then influence the CCWF indirectly. The specific possible influence mechanism is as follows:as the NAST shifts more northeastward,since it is far from the Asian westerly jet, which is unfavorable for the strong STEA over the North Atlantic region directly propagating by this westerly wave guide all the way to China. At the same time, the North American westerly jet shifts more northward (southward) and the index of North Atlantic Oscillation (NAO) is in its positive phase. The downstream STEA by propagating could cause the divergence of horizontal E-P fluxes over high latitudes and the convergence over middle latitudes, which will cause acceleration of westerly over high latitudes and deceleration of westerly over middle latitudes. As a result, the polar vortex will be confined to the polar region so that the cold air will be uneasy to move southward, and then the temperature of the low-level cold mass over the Siberian High will increase. All of the above anomalies occurred in circulation and propagation of STEA may finally contribute to the reduction of cold wave frequency in most stations of China and vice versa.