Effects of the East Asian subtropical westerly jet on winter persistent heavy pollution in the Beijing–Tianjin–Hebei region. (19th October 2021)

• Record Type: Journal Article
• Authors: Mei, Mei; Ding, Yihui; Wang, Zunya; Liu, Yanju; Zhang, Yingxian
• Is Part Of: International journal of climatology. Volume 42:Number 5(2022)
• Page Start: 2950
• Page End: 2964
• Publication Date: 2021-10-19
• Subjects: Beijing–Tianjin–Hebei region -- influence mechanism -- intra‐seasonal variation -- persistent heavy pollution episode -- PM2.5 -- subtropical westerly jet; Climatology -- Periodicals; Climat -- Périodiques; Climatologie -- Périodiques; 551.605
• DOI: 10.1002/joc.7400
• Languages: English
• ISSNs: 0899-8418

Abstract

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. Abstract : The meridional displacement and the intensity of SWJ could affect the whole life cycle of the persistent heavy pollution episodes over BTH region, especially the developing and peak stages. Triggered by the changing secondary circulation of SWJ at the entrance, intensive descending motion has established a favourable environment for the accumulation of pollutants in the developing stage. The anomalous southerly wind and moisture transport instead of the descending motion have played important roles in the peak stage.