Island Precipitation Enhancement in Radiative-Convective Equilibrium: Impacts on Large-Scale Circulation

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. Since rainfall over the islands of the Maritime Continent is 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. Previous idealized simulations with a cloud-system resolving model in small square domains have shown that small islands can affect both the spatial distribution of precipitation and the domain-average temperature of the troposphere. Here we seek to explore the impacts of islands on the large-scale circulation. We conduct simulations with the System for Atmospheric Modeling cloud-resolving model, where the domain is a highly elongated 3D channel, which has planetary scale in one horizontal dimension and cloud-system scale in the other. We find organization into a small number of large convectively active and suppressed regions, and discuss the simulated diurnal cycles of precipitation and clouds over land and ocean. Preliminary results suggest that an island that occupies only a few percent of the domain can substantially influence the location of large-scale convectively active and suppressed regions, analogs of ascending and descending branches of the Walker Circulation.