Response of early winter haze in the North China Plain to autumn Beaufort sea ice
Recently, early winter haze pollution in the North China Plain has been serious and disastrous, dramatically damaging human health and the social economy. In this study, we emphasized the close connection between the number of haze days in early winter in the North China Plain and the September–October sea ice in the west of the Beaufort Sea (R=0.51) via both observational analyses and numerical experiments. Due to efficient radiative cooling, the responses of atmospheric circulations partially manifested as reductions of surface wind speed over the Beaufort Sea and Gulf of Alaska, resulting in a warmer sea surface in the subsequent November. The sea surface temperature anomalies over the Bering Sea and Gulf of Alaska acted as a bridge. The warmer sea surface efficiently heated the above air and led to suitable atmospheric backgrounds to enhance the potential of haze weather (e.g., a weaker East Asian jet stream and a Rossby wave-like train propagated from North China and the Sea of Japan, through the Bering Sea and Gulf of Alaska, to the Cordillera Mountains). Near the surface, the weakening sea level pressure gradient stimulated anomalous southerlies over the coastal area of China and brought about a calm and moist environment for haze formation. The thermal inversion was also enhanced to restrict the downward transportation of clear and dry upper air. Thus, the horizontal and vertical dispersion were both limited, and the fine particles were apt to accumulate and cause haze pollution.