LAUSR

In this study, the authors conduct a detailed analysis of a prolonged fog and haze (FAH) event in the megacities of central and eastern China in January 2013. The persistence and intensification mechanisms of high impact FAH weather are analyzed using surface and sounding data from national meteorological observation stations and national environmental pollutant observations. The large-scale circulation was characterized by the weak and stable polar vortex in Eurasia, a zonally elongated circulation spanning from the midlatitudes to high latitudes at 500 hPa, and the West Pacific Subtropical High extending further westward. At the surface, the FAH regions were under control by a weak easterly and southeasterly at the back or bottom of the surface high-pressure system, which was favorable for the accumulation of high aerosol pollutant concentrations. The formation and intensification of the FAH have an apparent correlation with the variation in meteorological variables and aerosols. The strengthening of the extreme fog was due to a combination of advection and radiation effects, among which alternative temperature advection played the key role in the maintenance and deterioration of FAH. The boundary layer height indicated the strengthening and weakening of the FAH. The persistence of weak vertical wind shear in the middle-lower layer and weak vertical motion were favorable dynamic factors for the FAH.