Idealized large-eddy simulation sensitivity studies of sea and lake breezes

Numerical studies of sea and lake breezes are reviewed and gaps in our current understanding of these thermally-driven circulations are discussed. A numerical sensitivity study is conducted using large-eddy simulations to determine the dependence of sea- and lake-breeze speed and length scales to variations in the land-surface sensible heat flux, offshore background wind, initial atmospheric stability, and lake diameter. This study is the first to test the dependence of sea- and lake-breeze characteristics to variations in these geophysical variables using a three-dimensional large-eddy simulation capable of explicitly resolving boundary-layer turbulence and vertical motion near the sea-breeze front. This study provides new understanding on the sensitivity of sea and lake breezes to variations in the land-surface sensible heat flux, opposing background wind, and lake diameter as well as the complex interactions that occur among these geophysical variables. For the first time, the daytime life cycle of sea and lake breezes in the presence of variations in these variables is simulated, in contrast to many earlier studies that focused primarily on the mature midafternoon sea-breeze circulation. Significant spatial variability in the intensity and vertical structure of lake and sea breezes is noted in the large-eddy simulations. The critical value of an opposing wind at which a sea or lake breeze is destroyed by synoptic-scale pressure gradients is approximately 20% lower in this study than that documented in earlier numerical studies. The depth of sea and lake breezes has also been found to be highly sensitive to the magnitude of the opposing background wind. Finally, the results of this study show that lake breezes for small and medium-sized lakes evolve much differently than sea breezes during the afternoon due to a limited quantity of cool air over the lake.