Atmospheric Circulation And Forecast Related To The Change Of Haze Days In December And January In The Yangtze River Delta

The haze pollution in the Yangtze River Delta is serious,which has a significant impact on the society.In this paper,by utilizing statistical methods,the characteristics of haze in the Yangtze River Delta(YRD)in December and January are discussed,and the associated atmospheric circulation and local meteorological conditions anomalies are analyzed and compared with those in North China(NC).Finally,the meteorological conditions from the second version Climate Forecast System(CFSv2)are improved to predict the haze days in the YRD.The conclusions are as follows:(1)Haze pollution is more serious in the north of the YRD,and the regions with large interannual variations of haze pollution are consistent with the regions with serious haze pollution.From the perspective of the background field,in December,the northern part of the YRD shows weak subsidence;the YRD is located in the turning area of wind direction;the average temperature is above the zero degree;the precipitation in the south is larger than that in the north,which is consistent with the distribution of relative humidity.In January,the subsidence of the north of the YRD weakens;the relative humidity increases compared with that of last month;the temperature near the ground is still colder in the upper atmosphere and warmer in the lower atmosphere,but the temperature difference is decreasing;the height of planetary boundary layer is slightly higher;the precipitation increases compared with that of last month,which is consistent with the increase of relative humidity in this month.(2)In December,the haze pollution in the YRD is mainly modulated by Scandinavian teleconnection pattern,while the influence of this mode is weak in January.The adverse weather conditions in December and January limit the vertical and horizontal diffusion of haze pollution in the YRD,respectively.Compared with last month,the inverse correlation between precipitation anomaly and haze pollution is more stable in January.East Asian monsoon in December and January has a negative contribution to the haze pollution in the YRD,but the control power is weak.In contrast,the December haze pollution in NC is mainly modulated by the teleconnection pattern of East Atlantic/West Russia,while the influence of circulation mode in January is weak.The local conditions affecting haze pollution in December and January in NC are similar,and only the precipitation anomaly corresponding to the abnormal ascending movement in January has a positive contribution to haze days.(3)The meteorological factors from the CFSv2 of the United States are revised.These meteorological factors can significantly affect the diffusion conditions of haze pollution in the YRD.The sea surface temperature and the meteorological factors predicted in the model are used as the correction factors.The correlation coefficient between the corrected meteorological factors and the observed values is good.Using the improved anomalous anticyclone index,temperature difference between the north and the south index,precipitation index to fit the haze days in the YRD in December(January),it is found that the model using the revised indices is better than the model using the non-revised indices,and their correlation coefficients with the observed haze days are 0.66 and 0.63(0.70 and 0.66),respectively.It is proved that the revised meteorological indices can better improve the predictive performance of the haze days in the YRD.