The Effects of a Remote Atoll and Lagoon on the Marine Boundary Layer

The presence of an island is known to affect the marine environment in multiple ways depending on the size, shape, and particularly the topography of the island. The dominant effect is seen in the atmospheric boundary layer through the significant change in surface roughness and land surface heating, while steep topography on a small island may affect large scale systems such as tropical cyclones. In this study, we investigate the role of a small remote coral atoll, Diego Garcia, in the Indian Ocean in modifying the marine environment. Dropsonde measurements made near the island were used to identify the effects of Diego Garcia in wind reduction and moisture enhancement. A case analysis was made using measurements from 04 December 2011 to quantify horizontal and vertical extent and the magnitude of the effects. Additionally, high-resolution COAMPS simulations were used to examine the potential of using mesoscale model to quantify flow modifications by small islands. COAMPS was able to simulate the wind reduction by the island, but could not quantify its effect on low-level moisture. Finally, a comparison between the dropsonde nearby and rawinsonde measurements from the island reveals the deficiency of the island-based rawinsonde measurements in representing the marine environment.