摘要
An upswing in haze weather during autumn and winter has been observed over North and Northeast China in re- cent years, imposing adverse impacts upon local socioeconomic development and human health. However, such an increase in the occurrence of haze events and its association with natural climate variability and climate change are not well understood. To investigate the climatology of the meteorological factors associated with haze events and their natural variability, this study uses a meteorological pollution index called PLAM （Parameter Linking Air-qual- ity to Meteorological conditions） and ERA-Interim reanalysis data. The results suggest that high PLAM values tend to occur over southern parts of northem China, implying the weather conditions over this area are favorable for the occurrence of haze weather. For the period 1979-2014, the regional mean PLAM shows an overall increase across Beijing, Tianjin, and Hebei Province, and parts of Shanxi Province. Also, a periodicity of 28-34 months is found in the temporal variation of PLAM, which implies a potential association of PLAM with the stratospheric Quasi-Bian- nual Oscillation （QBO）. By using the QBO index during the autumn and winter seasons in the preceding year, an in- crease in PLAM is found for the westerly phases of the QBO, relative to the easterly phases. An upper-tropospheric warming is also found in the westerly phases, which can induce a stable stratification that favors the increase in PLAM across the midlatitudes. The modulations of large-scale environmental factors, including moist static stability, vertical velocity, and temperattu＇e advection, also act to enhance PLAM in the westerly phases. However, the baro- clinic term of moist potential vorticity at 700 hPa tends to decrease over the south, and an increase in low-level as- cent is found over the north. These factors can reduce PLAM and possibly limit the statistical significance of the in- creased PLAM in the westerly phases of the QBO.
An upswing in haze weather during autumn and winter has been observed over North and Northeast China in re- cent years, imposing adverse impacts upon local socioeconomic development and human health. However, such an increase in the occurrence of haze events and its association with natural climate variability and climate change are not well understood. To investigate the climatology of the meteorological factors associated with haze events and their natural variability, this study uses a meteorological pollution index called PLAM （Parameter Linking Air-qual- ity to Meteorological conditions） and ERA-Interim reanalysis data. The results suggest that high PLAM values tend to occur over southern parts of northem China, implying the weather conditions over this area are favorable for the occurrence of haze weather. For the period 1979-2014, the regional mean PLAM shows an overall increase across Beijing, Tianjin, and Hebei Province, and parts of Shanxi Province. Also, a periodicity of 28-34 months is found in the temporal variation of PLAM, which implies a potential association of PLAM with the stratospheric Quasi-Bian- nual Oscillation （QBO）. By using the QBO index during the autumn and winter seasons in the preceding year, an in- crease in PLAM is found for the westerly phases of the QBO, relative to the easterly phases. An upper-tropospheric warming is also found in the westerly phases, which can induce a stable stratification that favors the increase in PLAM across the midlatitudes. The modulations of large-scale environmental factors, including moist static stability, vertical velocity, and temperattu＇e advection, also act to enhance PLAM in the westerly phases. However, the baro- clinic term of moist potential vorticity at 700 hPa tends to decrease over the south, and an increase in low-level as- cent is found over the north. These factors can reduce PLAM and possibly limit the statistical significance of the in- creased PLAM in the westerly phases of the QBO.
