资源环境科技发展态势分析平台

Convection is highly active on tropical islands. Based on a 3-year radar climatology over Hainan Island, a mountainous tropical island in South China, we identified a distinct spatial dependence of convection initiation (CI) on the speed of the large-scale low-level flow. Convection initiates most prominently over the lee-side plains in high-wind conditions while over mountains in low-wind conditions. Quasi-idealized numerical simulations suggest that mountain ridges stimulate the formation and growth of horizontal convective rolls (HCRs) over the lee-side plains in high-wind conditions. These HCRs subsequently intersect with sea-breeze fronts, which enhances the low-level convergence favoring CI on the lee-side plains of the island. During low-wind conditions, thermally-driven circulations control and favor CI over the mountains during the day. The findings highlight that the response of local circulations to the lower-troposphere ambient flow and diurnal thermal heating is an important aspect of convection initiation on the island.