Effect of rainfall-induced diabatic heating over southern China on the formation of wintertime haze on the North China Plain

Abstract

Abstract. During the winters (December–February) between 1985 and 2015, the North China Plain (NCP) suffered many periods of heavy haze, and these episodes were contemporaneous with extreme rainfall over southern China; i.e., South Rainfall−North Haze events. The formation of such haze events depends on meteorological conditions, which are controlled by the atmospheric circulation associated with rainfall over southern China, but the underlying physical mechanism remains unclear. This study uses observations and model simulations to demonstrate that haze over the NCP is modulated by anomalous anticyclonic circulation caused by the Rossby wave train, in conjunction with the north−south circulation system (NSC), which ascends over southern China, moves north into northern China near 200–250 hPa, and then descends in the study area. Moreover, in response to rainfall heating, southern China is an obvious Rossby wave source, supporting waves along the subtropical westerly jet waveguide and finally strengthening anticyclonic circulation over the NCP. Composite analysis indicates that these changes lead to a stronger descending motion, higher relative humidity, and a weaker northerly wind, which favors the production and accumulation of haze over the NCP. A linear baroclinic model (LBM) simulation reproduced the observed NSC reasonably well and supports the diagnostic analysis. Quasi-geostrophic (QG) vertical pressure velocity (ω) diagnostics were used to quantify the contributions to the NSC made by large-scale adiabatic forcing and diabatic heating. The results indicated that the NSC is induced mainly by diabatic heating related to precipitation over southern China, and the effect of large-scale circulation is negligible. These results provide the basis for a more comprehensive understanding of the mechanisms that drive the formation of haze over the NCP.

Intraseasonal variation of the northeast Asian anomalous anticyclone and its impacts on air pollution in the North China Plain in early winter

“…In addition, it is well known that the wet deposition through scavenging by rainfall is an effective way to remove atmospheric aerosols and soluble gases (e.g., Atlas and Giam, 1988). When the NAAA appears, southern China tends to experience heavy rainfall and vice versa in the NCP (not shown) (e.g., Ma et al, 2018;An et al, 2020An et al, , 2021, which is only not conducive to the wet removal of aerosol in the NCP, but usually deteriorates air quality in the NCP via a local north−south circulation (not shown) (An et al, 2020(An et al, , 2021Mei et al, 2021).…”

“…Moreover, Cai et al (2017) found that global warming will further increase the incidence of haze days in China by reducing the wind strength. Specific to air pollution in the NCP, previous studies have found many influence factors, including sea surface temperature (Chang et al, 2016;Jeong et al, 2018;Yu et al, 2020), Arctic sea-ice (Wang et al, 2015, Zou et al, 2020, Eurasian snow cover and soil (Zou et al, 2017;Yin et al, 2018) and climate internal variability including the Eurasian Teleconnection (Li et al, 2019) and subtropical westerly jet waveguide (An et al, 2020(An et al, , 2021Mei et al, 2021), and so on. As a matter of fact, the northeast Asian anomalous anticyclone (NAAA) is directly related to air pollution in the NCP Callahan and Mankin, 2020).…”