Variation Characteristics And Causes Of Foggy Days In South China In Winter

In recent years,the fog damage occurs in southern China frequently.Previous studies indicate that El Ni(?)o-Southern Oscillation(ENSO)have a prominent effect on the winter fog days over eastern China,but no definite answer was founded on the relationship between fog days over southern China and ENSO.Also,it is still an unsolved-problem whether the ENSO-fog days relationship will change in different decades.Therefore,based on the observed daily fog data from 52 meteorological stations in southern China and ERA5reanalysis data from 1979 to 2016,the characteristics in spatial-temporal distribution of winter fog days over southern China(WFDSC)are investigated using the EOF analysis and other statistical methods.The possible ENSO-WFDSC relationship and also its interdecadal characteristics are further analyzed in this paper.Results are shown as follows:(1)The fog days over southern China mainly appears in winter,exhibiting a whole-region consistent pattern and displaying significant increasing trend and evident interannual variability.The interannual variation of WFDSC is closely related to the weakened northerly wind,more stable atmosphere and the decreasing T-T_dnear surface,which implies that the water vapor in air is increasing,providing favorable meteorological background fields for the maintenance and development of fog over southern China.(2)There is a close relationship between the interannual variability of WFDSC and ENSO,which mainly depends on heavy fog days rather than light fog days.During El Ni(?)o winters,an anomalous anticyclone tends to occur over the Philippine Sea,and the warm moist anomaly southwesterlies on the western flank of this anticyclone brings abundant water vapor to southern China,conducive to the fog formation.Roughly opposite changes of fog days occur during La Ni(?)a winters.(3)Modulating by the Atlantic Multidecadal Oscillation(AMO),the interannual ENSO-WFDSC relationship exhibits an obvious interdecadal change,that is,a significant positive correlation between the interannual variability of WFDSC and ENSO appears during the positive phase of AMO(before 1996),while no significant interannual ENSO-WFDSC relationship is founded during negative AMO phase(after 1996).We suggest that AMO could influence the interannual ENSO-WFDSC relationship by modulating the SST anomalies over western north Pacific and tropical Indian Ocean,which is the critical reason for the intensity and spatial extent of the anomalous anticyclone and cyclone over the Philippine Sea that affect the local maintenance of WFDSC during ENSO events.(4)The long-term variation of WFDSC shows a spatial difference,which means,the heavy fog days over most part of Guangxi province and the light fog days over the whole southern China display significant increasing trend,while the linear trend of the heavy fog days over Guangdong province and Hainan province are not significant.Further analysis shows that the long-term variation of WFDSC might be influenced by the variation of aerosol.