Numeral simulation of impacts of sea land breeze on the formation and dissipation of the Bohai Sea fog

Abstract

From 2019 to 2022, there were a total of 34 sea fog events in the Bohai Sea, among which sea land breezes (SLB) occurred 17 times (accounting for 50 %). The duration of fog in the presence of SLB ranged from 24 to 40 h, while fog without SLB lasted between 3 and 7 h. The SLB circulation significantly increased the duration of sea fog. Therefore it's necessity to study the impacts of SLB on fog formation and dissipation of the Bohai Sea. The Weather Research and Forecasting (WRF) model could simulate meteorological elements well, showing good reliability. Sensitivity experiments were carried out using the WRF model on two different types of SLB-fog. The numeral simulation results are showed as follows. Under the influence of land breeze, the vertical cloud liquid water (CLW) content increased 0.016–0.7 g kg⁻¹, the height of the boundary layer reduced 66.7 % ∼ 92.3 %, and temperature inversion layer was formed 0.5 km in the coastal and offshore areas of the Bohai Sea. Thus the sea fog was formed and the coastal fog intensity was enhanced affected by the land breeze. Under the influence of sea breeze, the height of the boundary layer increased 0.5–7 times and the temperature inversion layer disappeared or weakened in coastal cities. The influence of sea breeze on the transportation of CLW content was decreased 0.016–0.358 g kg⁻¹. Under the combined influence of factors such as CLW, temperature inversion, and boundary layer height, the sea breeze caused large-scale dissipation of sea fog in the Bohai Sea or hindered the expansion of the fog area. Numeral simulation of a typical case indicated that the increased CLW content (0.016–0.07 g kg⁻¹) under the influence of land breeze led to the formation of this sea fog. The intensity of the land breeze influenced the size of the fog area. In the near-surface layer of A Platform, the Richardson number (Ri) decreased 0.2–7.2 when affected by the sea breeze, which was conducive to the development of turbulence. The CLW content decreased by up to 0.71 g kg⁻¹. Therefore, the sea fog dissipated over a large area in the Bohai Sea under the influence of sea breeze. These findings suggest that the mesoscale circulation of SLB played an important role when the large-scale meteorological conditions were relatively weak.