Abstract:Based on the data of automatic weather station, wind profiling radar, ERA5 reanalysis, Himawari 8 high resolution satellite and FM 120 fog droplet spectrometer, we discuss the circulation pattern and microphysical characteristics of an sea fog event that happened in southern coastal area of Fujian Province on 7 April 2019. Circulation analysis shows that this sea fog event occurred under the control of west to northwest flow at 500 hPa trough bottom, while from 700 hPa to surface there was uniform southerly flow. The sounding situation was stable. Before sea fog event, low level wind speed decreased significantly, increasing the thickness of low wind speed. This situation provided stable circulation for sea fog. Himawari 8 satellite images show that the sea fog rapidly formed in the Taiwan Strait first and then advected to coastal area affected by low level southerly airflow. Hydrological analysis indicates that there existed a cold water band and large temperature gradient near the shore. Sea surface temperature (SST) varied between 18 ℃ and 24 ℃. The air and sea temperature difference was between 0 ℃-2 ℃ with sea surface colder than the air above, which contributed to the formation of advective sea fog. Fog droplet spectrum analysis shows that visibility decreased dramatically while particle number concentration (PNC), liquid water content (LWC) and droplet spectrum increased significantly at the same time. During the sea fog process, 5 min average PNC exceeded 200 cm-3 and instantaneously reached 468 cm-3 maximum, and the average PNC during the fog process reached 100 cm-3. The 5 min average LWC reached 0.41 g·m-3 and 1.35 g·m-3 instantaneously. The average LWC during the fog process reached 0.17 g·m-3. Fog droplet size featured double peaks with 4-6 μm and 22-26 μm intervals respectively during the fog process. This indicates that small and big particles both can contribute to the formation of sea fog. 