Study On The Role Of External Forcing From Sea Ice And Sea Surface Temperature On The Formation Of Severe Fog And Hazy Event In Winter In China

Based on the fog and haze data set of the National Meteorological Information Center from January 1981 to February 2017,NCEP/NCAR reanalysis data and sea ice and sea temperature data from the Hadley Center during the same period,the relationship between the changes of sea ice in the Karah Sea and Barents Sea and the sea temperature in the early autumn and the characteristics of winter fog and haze days in eastern China is analyzed.Sea ice in the Kara Sea and Barents Sea has an important influence on the mid-high latitudinal circulation in Asia.The low anomaly of sea ice in autumn is one of the reasons for the formation of the mid-high latitudinal anomalous zonal circulation in Asia in winter.In autumn,the sea ice in this area is less,the zonal circulation in mid-high latitudes of Asia is strong in winter,and the East Asian trough is weak,which affects the weakening of the East Asian winter monsoon in eastern China.This provides favorable conditions for the accumulation of atmospheric pollutants in the horizontal direction.At the same time,the troposphere is positive temperature anomaly from the middle to the bottom,and the difference between the troposphere and the surface temperature decreases,which makes the atmosphere more stable,and is not conducive to the vertical diffusion of atmospheric pollutants.The combined function of horizontal and vertical causes haze weather in eastern China.Although sea ice in the Kara Sea and Barents Sea is one of the important factors affecting the occurrence of winter haze in eastern China,it has no significant effect on the number of days of foggy weather in eastern China in winter.Compared with the meridional circulation index,the latitudinal circulation index in Asia can better reflect the change of fog-haze days in winter in eastern China.The stronger the latitudinal circulation in middle and high latitudes of Asia in winter,the more fog-haze days in eastern China.In terms of sea temperature,the SVD decomposition results of fog,haze and SST show that when SST is in the first mode positive phase,there are abnormal southwest wind and south wind transporting warm and wet water vapor to the south of China in the Central South Peninsula and the South China Sea.In the South China Peninsula and the South China Sea,there are abnormal southwesterly winds and southerly winds that transport warm and wet water vapor to southern China.Compared with the abnormal southerly winds in the South China Sea,the stronger abnormal southwesterly winds in the South China Peninsula transport aerosols,which provides conditions for the increase of haze days in southern China.When the SST is in the second mode positive phase,i.e.ENSO and IOD positive phase,the SST in the east-central equatorial Pacific Ocean and the western tropical Indian Ocean is higher,the SST in the tropical Pacific Ocean and the western Pacific Warm Pool is lower,and there are Philippine anomalous anticyclone over the south of the South China Sea and the North of the Philippines transporting water vapor to the south of China.Because the abnormal air flow is mainly warm and humid at sea,and the sea temperature in the South China Sea is low,the humidity in South China is higher than that in North China.The warm and humid air flow makes the haze in South China change to fog,so the number of haze days in South China decreases and the number of fog days increases.These two modes of SST have different effects on fog and haze in eastern China.Regression fitting of the first mode time coefficient of SST is very important for the formation of fog and haze in eastern China.