Relationship between the Early-Spring Low-Temperature Enhancement in North China and Sea Surface Temperature in the North Atlantic since the 1990s

Based on reanalysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF) and sea-surface temperature (SST) data from the Hadley Center (Hadley), in this paper, we present our analyses and determination of the reason for the extreme low-temperature events of the North China’s enhancement in spring since the 1990s, which we verified by numerical simulation. The results indicate a significant correlation between the North Atlantic “Horse Hoof” SST mode and the Eurasian (EU) wave train, which could be a factor in North China’s extreme low-temperature events. The SST mode was also found to be closely correlated with the vertical wave energy in key areas of the North Atlantic after 1997. The 500-hPa circulation mode in the North Atlantic for the same period showed a trend of eastward movement and southward withdrawal. Since 1997, the expansion of the regional scope of positive surface temperature forced by thermal anomalies adjacent to eastern Greenland, as well as increases in the westerly jet stream, could have stimulated the EU pattern and generated warm ridges downstream of the Eurasian continent. The results obtained using the localized multiscale energy and vorticity analysis (MS-EVA) method revealed that the forces of the surface thermal anomalies and the pressure gradient in the key area of eastern Greenland have had a positive effect on the whole troposphere, which have led to an increase and divergence of high-level kinetic energy and a strengthening of the ridge toward the north. Via the EU wave train, the cyclonic anomaly was strengthened downstream from North China, and the Asian polar vortex was both strengthened and maintained. The temperature in North China decreased sharply, which increased the number of extreme low-temperature events. Finally, we used the CAM5.1 model to simulate the effects of the North Atlantic “Horse Hoof” SST mode on the atmospheric circulation anomalies and the extreme low temperatures in North China. We found the simulation results to agree well with the observation results. This further confirms that the SST mode can affect the atmospheric circulation anomalies in Eurasia by stimulating the EU wave train, thereby leading to the intensification of cyclones and meridional circulation, as well as increasing the number of extreme low-temperature events in North China.