Interannual relationship between displacement and intensity of East Asian jet stream and haze over eastern China in winter

Abstract

A recent case study indicated that the weakening of the East Asian subtropical jet was an important cause of the severe haze in North China in the winter of 2015. However, the interannual relationship between two key features, the displacement and the intensity of the East Asian jet stream (EAJS) and the haze days over eastern China (HD_EC), remains unclear. Observed data, ERA-Interim reanalysis, and Community Earth System Model Large Ensemble Numerical Simulation(CESM-LENS) were used to investigate the interannual relationship between the EAJS and HD_EC during the winter season from 1980 to 2017 and its possible associated atmospheric mechanisms. The results show that the northward movement of the EAJS is conducive to more HD_EC by weakening synoptic-scale transient eddy activities (STEA) and baroclinicity, forming an upper-level anticyclonic anomaly over eastern China (EC). The local meteorological conditions (e.g., stronger temperature inversion potential, higher relative humidity, descending motion) are favorable for the accumulation of HD_EC, showing consistent variations in more haze in the entire region of EC. The southward movement of the EAJS has the opposite effect. The strong East Asian subtropical jet (weak polar-front jet) could result in the distribution of the meridional dipole with less haze in north EC and more haze in south EC. The mean flow loses energy to the STEA over north EC and increases the baroclinicity, which is favorable for dispersing HD_EC. However, the configuration of upper-level cyclonic and low-level southwest wind anomalies that appeared in south EC weakened the STEA, which favored the accumulation of HD_EC. The observed results were further verified by CESM-LENS.

Keywords: CESM-LENS; East Asian jet stream; Eastern China; Haze days.