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Effects of the East Asian subtropical westerly jet on winter persistent heavy pollution in the Beijing–Tianjin–Hebei region
Author(s) -
Mei Mei,
Ding Yihui,
Wang Zunya,
Liu Yanju,
Zhang Yingxian
Publication year - 2022
Publication title -
international journal of climatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.58
H-Index - 166
eISSN - 1097-0088
pISSN - 0899-8418
DOI - 10.1002/joc.7400
Subject(s) - subtropical ridge , siberian high , climatology , environmental science , atmospheric sciences , westerlies , sink (geography) , zonal and meridional , subtropics , atmospheric instability , beijing , east asia , geology , wind speed , meteorology , precipitation , geography , oceanography , cartography , archaeology , fishery , china , biology
Based on the daily average concentration of PM 2.5 , 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.