Sea Fog under the North Wind with the Influence of Foehn Wind in the Okhotsk Sea

The Okhotsk Sea is renowned as one of the world's most foggy regions. Previous studies have identified that sea fog occurring under south winds is mainly advection fog. However, the formation mechanism of sea fog under north winds remains unclear. On August 21, 2019, the research vessel "Xiangyanghong 01" observed a phenomenon where low clouds transformed into sea fog in the waters north of the Kuril Islands under north wind . Analysis of shipborne observations, reanalysis data, and simulation results show that during this sea fog event, the upper-level atmospheric circulation over the Pacific was characterized by a cut-off low and blocking high. The stable circulation provided favorable conditions for the sea fog within the Okhotsk Sea. From August 19 to 21, influenced by east winds between tropospheric systems, the east-west mountain flow over the Kamchatka Peninsula intensified continuously. The Foehn effect on the western coast of the peninsula led to a significant increase in air temperature, enhancing the advection of warm air from land to sea, particularly between 925 hPa and 950 hPa. As this warm dry air ascended above the moist air mass over the sea, it strengthened the temperature inversion and lowered the inversion layer base, thereby promoting cloud descent and the formation of sea fog. Furthermore, under north winds, the subcloud air mass experienced evaporation of warm sea surface and cooling of cold sea surface of the eastern Okhotsk Sea. The subcloud air mass became saturated with moisture, leading the downward development of the cloud layer into sea fog.