A numerical study of the convection triggering and propagation associated with sea breeze circulation over Hainan Island

摘要

Based on high-resolution numerical simulations, the effects of sea breeze circulation (SBC) on associated convective initiation and propagation over Hainan Island are investigated. The results show that the blocking of synoptic wind on the windward side of the mountains inhibits the occurrence of windwardside valley breeze and sea breeze. In the context of low mountains, weak synoptic wind not only favors the combination of the SBC with the valley breeze circulation on the leeward side of the mountains but also makes the convergence zone between the synoptic wind and the leeward-side combined circulation stay near the tops of the mountains, leading to the accumulation of large quantities of water vapor taking place over the mountaintops. The combined effect of enhanced water vapor and high temperatures over the mountaintops can result in the generation of much larger convective available potential energy (CAPE) than the surrounding areas. The coupling of the large CAPE with the considerable converging ascending motion and abundant water vapor near the tops of the mountains promotes the occurrence of a strong convection band (CB) over the mountaintops. During the CB propagation under the steering of synoptic wind, the flow across the CB continuously and strongly opposes the SBC front and the fronts of the Kelvin-Helmholtz billows behind, resulting in successive and strong lifting motion as well as large quantities of water vapor and high CAPE near these fronts. These lead to an apparent downstream wave-like propagation of the CB.