A large-eddy simulation study of deep-convection initiation through the collision of two sea-breeze fronts

Abstract

Abstract. Large-eddy simulations are performed to investigate the process of deep-convection initiation (DCI) over a peninsula. In each simulation, two sea-breeze circulations develop over the two coasts. The two sea-breeze fronts move inland and collide, producing strong instability and strong updrafts near the centerline of the domain, and consequently leading to DCI. In the simulation with a maximum total heat flux over land of 700 or 500 W m−2, DCI is accomplished through the development of three generations of convection. The first generation of convection is randomly produced through the collision of the sea-breeze fronts. The second generation of convection is produced mainly through the collision of the sea-breeze fronts, but only develops in regions where no strong downdrafts are produced by the first generation of convection. The third generation of convection mainly develops from the intersection points of the cold pools produced by the second generation of convection, and is produced through the collision between gust fronts and sea-breeze fronts. As the maximum total heat flux decreases from 700 to 500 W m−2, both the height and strength of the sea breezes are reduced, inhibiting the forcing of the first two generations of convection. These two generations of convection therefore become weaker. The weaker second generation of convection produces shallower cold pools, reducing the forcing of the third generation, and consequently weakening the third generation of convection. As the maximum total heat flux further decreases to 300 W m−2, only one generation of shallow convection is produced.