Title: Island Rainfall in Radiative-Convective Equilibrium: Idealized Modeling and Theory

Abstract: Tropical islands are observed to be rainier than nearby ocean areas, and precipitation over the islands of the Maritime Continent plays an important role in the atmospheric general circulation. Rainfall over tropical islands is also strongly modulated by the diurnal cycle of solar insolation and surface enthalpy fluxes, so the poor representation of the diurnal cycle of convection in climate models may be a significant source of model biases, both locally and remotely. Since rainfall over the islands of the Maritime Continent is also strongly correlated with ENSO, it is possible that changes in island areal extent in the region over geologic timescales has had a significant effect on the strength of the Walker Circulation and the distribution of tropical rainfall.

To explore these issues, I have conducted simulations of radiative-convective equilibrium with the SAM cloud system resolving model, where a highly idealized circular island is embedded in a slab-ocean domain. I find that the precipitation rate over the island can be more than double the domain average value, with island rainfall occurring primarily in an intense, regular thunderstorm system that occurs in the afternoon to early evening each day. Island size affects the magnitude of simulated island rainfall enhancement, the intensity of the convection, and the timing of the rainfall maximum relative to solar noon. I discuss both dynamic and thermodynamic mechanisms for the enhancement of island rainfall, including the important finding that that the upper troposphere typically warms with the inclusion of an island, which may have implications for large-scale overturning circulations in the tropics. I also attempt to use and extend the linear theory of the land-sea breeze as a tool for understanding my results.