Influences of atmospheric intraseasonal oscillation in mid-high latitudes on winter haze pollution over the Beijing-Tianjin-Hebei region

This paper analyses the intraseasonal evolution of the winter haze pollution over the Beijing-Tianjin-Hebei (BTH) region in China between 1979 and 2013, and the influences of the atmospheric intraseasonal oscillations (ISOs) in mid-high latitudes. Two significant ISO signals of 10-20-day and 20-40-day are identified from the winter haze pollution over the BTH region, and their superposition notably contributes to the occurrence of haze pollution. On the 10-20-day timescale, the haze pollution is intimately associated with a mid-high-level southeastward propagating wave train that originates from the North Atlantic. With the wave evolution, an anomalous anticyclone reaches the Korean Peninsula-Japan, leading to strong descents and anomalous southerly winds over the BTH region, favourable for haze pollution. On the 20-40-day timescale, the atmospheric wave train originates from the eastern North America, propagates eastward to the northwestern Lake Baikal, and then turns southward to the northeastern China-Japan. The peak stage of the haze pollution is related to the resultant zonal dipole, with the anomalous cyclone over the northwestern Lake Baikal and the anomalous anticyclone over the northeastern China-Japan. The dominance of the mid-upper tropospheric anticyclone over the BTH region suppresses the development of convection, thus hindering the vertical diffusion and wet deposition of pollutants. Moreover, the anomalous westerly winds between the dipole weaken the incursion of cold mass from higher latitudes, thus further contributing to the peak of haze pollution.