Numerical modelling of the offshore extent of sea breezes

Two‐ and three‐dimensional versions of a nonlinear atmospheric model were used to investigate environmental controls on the offshore influence of sea‐breeze circulations. The temperature of the water surface relative to the atmospheric temperature had a small effect when the water was colder than the overlying air, and a greater effect when the water temperature was high enough to create convective mixing in the planetary boundary layer over the water. Ambient thermal stratification, including elevated inversions with thermal stratification similar to trade wind inversions, had a small influence. The predicted offshore extent of the sea breeze was substantially affected by latitude. The effects of both ambient stratification and latitude were generally consistent with predictions of linear theory. Prevailing synoptic winds were also found to have a significant effect on the sea breeze offshore, with offshore influence greatly suppressed by onshore large‐scale flow. Curvature of the coastline produces slightly stronger winds offshore for a concave coast than for a convex coast. The subsidence offshore also extends further over the water for a concave coast than for a convex coast. The model predictions were compared with previous investigations which used linear theory. It was found that the present results agreed with the linear theory of R. Rotunno with regard to the effects of latitude and ambient thermal stability. Linear theory is less suitable for explaining the effects of water temperature, owing to the simplified treatment of turbulent exchange necessary for a tractable linear model.