Abstract:Using observation data from automatic weather station (AWS), ERA5 reanalysis data, Himawari 8 satellite data and multi-source observation data at Xiangan Station, We analysis the circulation situation, Evolution characteristics and microphysical structure of a sea fog event in Southern Fujian Coastal Area(SFCA) on April 1th, 2021. Result shows this is a typical advection fog event. Multiple weather conditions providing the stable circulation situation and abundant water vapor conditions for the occurrence and development of sea fog, which were the west-southwest airflow at 500hPa, the low layer was controlled by consistent southwest airflow and anti-cyclonic sinking airflow, the temperature inversion layer derived from sounding. Low level cloud and sea fog change into each other during the whole event. Daytime was dominated by low level cloud while after sunset, low level cloud changes into fog with temperature dropping and wind blast. Fog changes into low level cloud while west wind dominates. Micro physical analysis shows that average fog droplet number concentration(N) was 52.4 cm-3, the average fog droplet liquid water content(LWC) was 0.084 g·m-3, the mean diameter(MD) was 9.4 μm during this event. The maximum of the average N per minute and the average LWC per minute were 132.6 cm-3 and 0.7321 g·m3. Spectrum of N and LWC at different stages exhibits quite different characteristics, which the size distribution of N was mainly a unimodal structure with the peak diameter at 4~6 μm in the preliminary, development and dissipation stages, and it was a bimodal structure with the main peak at 4~5 μm and the secondary peak at 24~26 μm of the maturity stage. In parallel to LWC, the size distribution characteristics are reversed, with the main peak at 24~26 μm and the secondary peak at 5~6 μm. It reveals that the N should dominantly influenced by small particles, the greatest influence to LWC is fog droplets of 20~30 μm. Comparative analysis of size distribution at the development and maturity stages shows that the main reason for the further deterioration of visibility should be the significant increase in LWC which led by the increase in the particle at 20~30 μm.