Abstract/Summary

Convective cloud bands known as “cloud trails” (CTs), are commonly found downwind of small islands (<O(100) km2) throughout the world. They occur primarily in the afternoon, and are known to form in response to land-sea contrasts under the presence of background flow. A set of idealised numerical experiments with 100 m horizontal grid spacing are performed to quantify the relationship between the surface forcing produced by an island and the strength of the resulting CT circulation. These experiments are based on observed environmental conditions for which a CT occurred off Bermuda, a small subtropical island. For these simulations, the CT circulation is found to be controlled by the strength of the integrated excess heating of the flow as it passes over the island. This excess heating is in turn controlled by the strength of the island heat fluxes when the wind speed and the island geometry are kept constant. Our experiments show, all-else-equal, a linear relationship between CT circulation strength and the island surface heat flux.