-1. During the advection fog period, the wind speed was 4 to 6 m·s-1 due to the influence of easterly wind. (3) In the frontal fog stage, the water vapour convergence centre was located from the South bank of the Qiongzhou Strait to the northeast land of Hainan Island, and the fog began to develop on the land. In the advection fog stage, the water vapour convergence centre was located from the North bank of the Qiongzhou Strait to the east of Hainan Island, and the fog developed from the sea. (4) In the frontal fog stage, the inversion layer developed at the height of about 950 hPa, which was an advection configuration of cold in the lower part and warm in the upper part. In the advection fog stage, warm advection occurred below 950 hPa, and the inversion layer developed from the ground. The development of two kinds of fogs with different properties, frontal fog and advection fog, maintained the fog for a long time."/>