Possible Dynamic Mechanisms of High- and Low-Latitude Wave Trains Over Eurasia and Their Impacts on Air Pollution Over the North China Plain in Early Winter

The Rossby wave train in boreal winter sometimes bifurcates into two branches near the Mediterranean, sometimes not. However, causes for bifurcating of the wave train are still being debated. Additionally, discussions about the differences in the deterioration ability of these wave trains on air pollution are also insufficient. This study uses the empirical orthogonal function (EOF) to obtain two dominant modes of the November-January season wave trains over Eurasia and discusses their different influences on air pollution over the North China Plain (NCP). From the EOF1 mode, bifurcation of the wave train appears to stem from the Rossby wave reflection near the Mediterranean because the Rossby wave source is located outside of a strong absolute vorticity gradient. From the EOF2 mode, the wave train propagates only along the subtropical westerly jet because the Rossby wave source is located inside of a strong absolute vorticity gradient, so that the wave train tends to be refracted near the Mediterranean. In addition, the wave train associated with the EOF1 is suggested to be related to the eastern Pacific El Nino. The eastern Pacific El Nino tends to force a wave train propagating into East Asia under the charger effect from positive feedback of air-sea coupling near the far eastern Atlantic and Mediterranean, while the wave train associated with the EOF2 is suggested to be mainly induced by natural internal variability. Furthermore, the results indicate that the bifurcation type wave train tends to cause higher PM2.5 concentrations over the NCP through a strengthened Northeast Asia anomalous anticyclone.

Automated summary

This study uses the empirical orthogonal function (EOF) to analyze the wave trains over Eurasia in boreal winter. It finds that the bifurcation of the wave train is related to the Rossby wave reflection near the Mediterranean, while the non-bifurcated wave train is mainly influenced by natural internal variability. The wave train associated with the EOF1 mode is suggested to be related to the eastern Pacific El Nino, while the wave train associated with the EOF2 mode is mainly induced by natural internal variability. The bifurcation type wave train tends to cause higher PM2.5 concentrations over the North China Plain.