Abstract
Abstract. Severe haze occurred in the North China Plain (NCP) from November to December 2015, with a wide spatial range and long duration. In this paper, the combined effect of the anomalous stationary Rossby waves within two westerly jet waveguides on this haze event in the NCP is investigated based on observational visibility data and NCEP/NCAR reanalysis data. The results show that circulation anomalies in Eurasia caused by the propagation of anomalous stationary Rossby wave energy along two waveguides within the westerly jet originating from the Mediterranean were responsible for haze formation in the NCP. The Rossby waves propagated eastward along the subtropical westerly jet and the polar front jet, causing an anomalous anticyclone over the Sea of Japan and anticyclonic wind shear at 850 hPa over the NCP, which enhanced the anomalous descent in the middle and lower troposphere and subsequently resulted in a stable lower atmosphere. Furthermore, the anomalous stationary Rossby waves propagating along the polar front jet weakened the East Asia trough and Ural ridge and strengthened the anomalous southerly wind at 850 hPa over the coastal areas of eastern China, decelerating the East Asia winter monsoon. The above meteorological conditions modulated haze accumulation in November and December 2015. Meanwhile, continuous rainfall related to ascending motion due to Rossby wave propagation along the waveguide provided by the subtropical westerly jet occurred in a large area of southern China. The associated latent heat release acted as a heat source, intensifying the ascending motion over southern China so that the descending motion over the NCP was strengthened, favoring the maintenance of severe haze. This study elucidates the formation and maintenance mechanism of large-scale haze in the NCP in late fall and boreal winter.
Highlights
Haze is the phenomenon of reduced visibility caused by the increase in aerosols or the hygroscopic growth of aerosols at a high relative humidity (Ma et al, 2014)
Haze was defined as a day when the daily mean visibility and relative humidity were less than 10 km and 80 %, respectively, and no rain, snow, sand and dust storms occurred in accordance with the standards set by the CMA (China Meteorological Administration, 2010)
A period of severe haze pollution occurred in the North China Plain (NCP) in November and December 2015
Summary
Haze is the phenomenon of reduced visibility caused by the increase in aerosols or the hygroscopic growth of aerosols at a high relative humidity (Ma et al, 2014). Fog is a phenomenon of reduced visibility caused by condensation of water vapor in the air near the ground (Wu et al, 2013). When fog and haze appear at the same time, it is called haze fog. In December 2015, the air quality was poor in the North China Plain (NCP), especially in the Beijing–Tianjin–Hebei region Y. Zhang et al, 2016; G.
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