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, 30–40.5∘ N, 112–121.5∘ E) 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 related to 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 two Rossby wave trains, in conjunction with the north–south circulation system, 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 simulation reproduced the observed north–south circulation system reasonably well and supports the diagnostic analysis. Quasi-geostrophic vertical pressure velocity diagnostics were used to quantify the contributions to the north–south circulation system made by large-scale adiabatic forcing and diabatic heating (Q). The results indicated that the north–south circulation system 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.

Possible Dynamic Mechanisms of High‐ and Low‐Latitude Wave Trains Over Eurasia and Their Impacts on Air Pollution Over the North China Plain in Early Winter

“…As shown in Figure 11a, there is a bulky anticyclonic anomaly at 500 hPa over Northeast Asia, which is accompanied by anomalous southeasterly winds at 850 hPa in the NCP. According to previous studies, wave trains related to El Niño can influence the anticyclonic anomaly over Northeast Asia in early winter (An, Sheng et al., 2022; An, Wang et al., 2022; Hu et al., 2018; Yu & Sun, 2018, 2020; Zhao et al., 2021 which supports our previous view, namely EOF1‐related wave train might be induced by the eastern Pacific El Niño. Under the control of this anticyclonic anomaly, the atmospheric boundary layer is shallow and surface convergence is strong (Figure 11c), which are conducive to the accumulation of pollutants and thus lead to higher PM 2.5 concentrations over the NCP (Figure 12e).…”

“…In addition, An et al. (2020, 2021) found that a local south‐north vertical circulation (c.f., Figure 1 of An, Sheng et al., 2022; An, Wang et al., 2022) due to heavy rainfall in southern China is also in favor of air pollution over the NCP. To further check these findings in this study, we show regression maps of precipitation in southern China and the local vertical circulation in Figure 12a−12d.…”

“…In addition, many previous studies suggested that the wave train along the polar front jet, the subtropical westerly jet wave train, or a combination of the two plays an important role in air pollution (or haze) over the North China Plain (NCP, 32°N−42°N, and 110°E−120°E) in autumn and winter (e.g., Li, Zheng et al., 2019; Li, Sheng et al., 2019; Wang et al., 2019; Chen et al., 2019; An et al., 2020, An, Sheng, et al., 2022). An et al.…”

Intraseasonal variation of the northeast Asian anomalous anticyclone and its impacts on PM<sub>2.5</sub> pollution in the North China Plain in early winter

“…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, , 2022, which is not only conducive to the wet removal of aerosol in the NCP but usually deteriorates air quality in the NCP via a local northsouth circulation (not shown) (An et al, 2020(An et al, , 2022Mei et al, 2021).…”

“…Specific to air pollution in the NCP, previous studies have found many influence factors, including El Niño (Chang et al, 2016;Jeong et al, 2018;Yu et al, 2020;Zeng et al, 2021), Arctic sea-ice (Wang et al, 2015;Zou et al, 2020), Eurasian snow cover and soil (Zou et al, 2017;Yin and Wang, 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, , 2022Mei et al, 2021), etc. Studies also revealed that the aerosol pollution over the NCP during coronavirus disease 2019 was related to the northeast Asian anomalous anticyclone (NAAA) (Ren et al, 2021).…”