Interannual variation in the number and severity of autumnal haze days in the Beijing-Tianjin-Hebei region and associated atmospheric circulation anomalies

In contrast with the considerable number of studies on the variability of winter haze pollution over eastern China, there have been few studies of autumnal haze in this region. The interannual variability of autumnal (September-November) haze days in the Beijing-Tianjin-Hebei region (AHD(BTH)) is significantly correlated with the Scandinavia-central Siberia-Western Pacific (SCSWP) teleconnection pattern, a quasi-barotropic atmospheric circulation anomaly. The SCSWP teleconnection pattern may therefore be a useful indicator for forecasting AHD(BTH). The positive phase of the SCSWP teleconnection pattern enhances the anomalous anticyclonic circulation centered over the Western Pacific via the southeastward propagating Rossby wave train emanating from Scandinavia. The positive SCSWP teleconnection pattern, together with the northward shift of the East Asian jet stream induced by low-level atmospheric baroclinicity, could provide the favorable local meteorological circumstances (i.e., suppressed cold air activity, higher surface temperatures and low-level atmospheric inversion, and lower planetary boundary layer height and decreased surface wind speed) required to explain the recent increased incidence of AHD(BTH).