Effects of the East Asian subtropical westerly jet on winter persistent heavy pollution in the Beijing–Tianjin–Hebei region

Abstract

Based on the daily average concentration of PM2.5, 15 typical persistent heavy pollution episodes (PHPEs) in the Beijing–Tianjin–Hebei (BTH) region during the winters of 2013–2019 are identified. And then the impact of the intra‐seasonal variations of the 200‐hPa subtropical westerly jet (SWJ) on the PHPEs is investigated. The results show that the SWJ affects the lifecycle of the PHPEs in the BTH region mainly through the meridional shift and intensity variation. In particular, the intensity variation has a closer relationship with the vertical velocity and low‐level meridional wind to affect the PHPEs. In the developing stage of the PHPEs, the SWJ shifts northward and strengthens. The BTH region is on the left side of the entrance of the SWJ and the vertical secondary circulation intensifies the descending motion in situ. As a result, the atmospheric boundary layer is compressed to sink rapidly, a temperature inversion in the lower levels appears and the atmospheric stability is enhanced. Finally, the atmospheric environment is favourable for the rapid accumulation of pollutants and the occurrence of the PHPEs. In the peak stage, the southward withdrawal and weakening of the SWJ favour the anomalous ascending motion and low‐level southerly anomalies over the BTH region. The dominant role of the dynamic descending motion is replaced by the low‐level southerly anomalies to enhance the PHPEs, by transporting more warm‐humid air to the BTH region. In the weakening stage, the SWJ moves northward and intensifies again. The low‐level southerly anomalies weaken to contribute to the dissipation of the pollutants.

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).…”

“…The first EOF mode (EOF1) represents the NAAA (Fig. 1a), which explains a total variance of 44.2 % and is well separated from the other eigenvalues as per the criterion of North et al (1982). To obtain the typical NAAA on the intraseasonal timescale, the NDJ 8-90 d Butterworth bandpass-filtered daily geopotential height anomaly field at 500 hPa in the region 25-55 • N, 100-160 • E is projected onto the EOF1 to obtain a daily principal component (PC) time series.…”

“…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).…”

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).…”