Analysis of a Heavy Fog Weather Process along Coast of Southern Fujian and Xiamen Airport Based on Multi-Source Observation Data
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Abstract:
Using the data from ground automatic stations, the Kuihua 8 satellite, radiosonde, wind profile radar, microwave radiometer, automatic observation system minute-by-minute observation, and ERA5 reanalysis, the generation and dissipation mechanism of a thick fog process on 6 March 2024 along the coast of southern Fujian and Xiamen Airport is analysed. The results show that during the formation of the fog, the surface was under a weak pressure field ahead of the cold front, with unified southwest warm and moist air currents prevailing in the middle and lower atmospheric levels. The heavy fog first appeared on the eastern sea surface, and there was a cold water zone in the Taiwan Strait. At 1000 hPa, there was strong warm advection in the Taiwan Strait, which was superimposed on the cold water zone to produce advection cooling fog. The temperature difference between the sea and air near the sea was between 0 and 3.2 ℃. After its formation, the sea fog spread westward to the land at night, showing a good spatiotemporal coupling relationship with the westward advance of the 1000 hPa warm advection. The formation of a nocturnal surface inversion and the increase in the thickness of the weak wind layer provided stable stratification conditions for the generation and development of the fog, while the long-term water vapour saturation at the surface provided sufficient moisture conditions for the generation and development of the fog. High-resolution satellite data monitored the evolutionary process where the sea fog spread from Kinmen and Xiang’an to Xiamen Airport at night, after which the fog in Xiamen Airport and its nearby small area dissipated while the sea fog persisted. Xiamen Airport experienced heavy fog from 03:22 to 04:47 (Beijing Time) on the 6th, lasting approximately 1.5 hours. With rapid onset and dissipation, it was classified as an explosive heavy fog event. The short-term sudden changes in surface wind direction and the sudden increase in wind speed at Xiamen Airport enhanced the local cold advection transport, introducing cold air from Tong’an Bay on the northeast side into the airport, accelerating the condensation of water vapour in the near-surface layer of the airport, which was an important thermal factor for the explosive formation of the heavy fog. The enhanced long-wave radiation before the fog was another thermal cooling factor. Analysis shows that the diffusion of the fog mass in Tong’an Bay combined with the “trumpet-shaped” terrain caused passive adjustment of the wind direction at the airport, and the propagation of fluctuations from the upstream cold air southward led to short-term changes in the wind at Xiamen Airport.