Possible Influence of the Variation of the Northern Atlantic Storm Track on the Activity of Cold Waves in China during Winter

On the basis of daily mean temperature data from 566 National Meteorological Information Center stations and National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data during 1961-2011, an investigation was conducted into the relationship between the variation of the winter North Atlantic Storm Track (NAST) and the frequency of cold waves in China on the annual timescale. The results from singular value decomposition analysis show that, on the annual timescale, the position of the NAST is closely linked to the cold wave frequency in winter: When the NAST moves northeastward (southwestward), the cold wave frequency at most stations decreases (increases) significantly, but the correlation between the intensity of the NAST and the cold wave frequency is low. Further analysis indicates that change in the NAST position may lead to anomalous propagation of the Synoptic-Scale Transient Eddy Activity (STEA). This could not only affect the cold air activity of China directly, but, after first having an impact on the general circulation via feedback, it could also have an indirect influence. The possible mechanism of influence is as follows: As the NAST shifts more northeastward (southwestward), it is far from (close to) the Asian westerly jet, which is unfavorable (favorable) for the direct propagation of strong STEA over the North Atlantic region via this westerly waveguide all the way to China. Meanwhile, the North American westerly jet shifts more northward (southward) and the index of the North Atlantic Oscillation is in its positive (negative) phase. Via propagation, the downstream STEA could cause the divergence (convergence) of horizontal Eliassen-Palm fluxes over high latitudes and the convergence (divergence) over mid-latitudes, which in turn will cause acceleration (deceleration) of the westerly over high latitudes and deceleration (acceleration) of the westerly over mid-latitudes. As a result, the polar vortex will (will not) be confined to the polar region so that the cold air will uneasily (easily) move southward, and then the temperature of the low-level cold mass over the Siberian high will increase (decrease). All of the above anomalies occurring in the circulation and propagation of STEA may ultimately contribute to the reduction (enhancement) of the cold wave frequency at most stations in China.