Abstract:

Using encrypted automatic stations, reanalysis data and satellite fog retrieval data, the spatial and temporal distribution characteristics of sea and land fog on the west coast of Bohai Sea from 2015 to 2020 were analyzed, and a typical case was selected to carry out sensitivity numerical experiments.The results show that the number of land fog is greater than that of the sea fog in autumn and winter on the west coast of Bohai Sea.The opposite results are true in spring and summer.Although the amount of sea fog and land fog in winter are the largest and the variation trend is the same, the distribution of land and sea fog still have significant local characteristics.The probability of fog bounded by the coastline on the west coast of Bohai Sea is more than 53%, most of them occur at the night, and the duration time is less than 12 h.The case analysis shows that the sea and land wind circulation transport the warm and humid air from the sea to the low altitude of the inland, the humidity increases rapidly to near saturation, and the weak cold air intrusion and the cooling due to the long wave radiation at night work together, leading to the formation of the inland fog.However, the sea fog is difficult to form due to high sea surface temperature (SST) and slow cooling of ocean atmosphere.The results of the SST sensitivity test also show that when the SST increases by 5%, the fog area that slightly enters the offshore area in the control experiment basically rewinds to the west of the coastline, and when the SST decreases by 5%, the land fog spreads to the whole Bohai Sea and maintains.High SST is the key factor that the land fog does not expand into the sea.

Key words: Sea fog, Land fog, Sea and land wind, Vertical circulation, Sea surface temperature (SST)