Weak cooling of the troposphere by tropical islands in simulations of the radiative‐convective equilibrium

Abstract

AbstractWe assess whether tropical islands tend to warm or cool the troposphere. To this end, we use idealized simulations of the radiative‐convective equilibrium employing a simulation domain that contains flat tropical islands represented by a land surface scheme. Results show more frequent precipitation over land as coastal breezes establish, and gravity waves triggered by afternoon convection propagating away from the islands. These waves horizontally homogenize density and in doing so communicate convectively induced temperature anomalies from the islands onto the ocean. What is the influence of the islands on tropospheric temperature? The diurnal surface warming of the islands tends to push the afternoon convection over land towards a warmer moist adiabat and, along with it, the temperature profile of the troposphere. However, at the same time, drying of the land surface pulls it towards a colder moist adiabat. All in all, we find that islands cool rather than warm the troposphere. More specifically, we obtain a weakly colder domain‐mean troposphere during episodes with a larger share of precipitation over land, or when the prescribed land fraction is increased. In particular, we find that the cooling becomes more pronounced over large islands. Overall, the results indicate that the inability of evaporation to keep up with the daytime surface warming over land, in contrast to the ocean, is of key relevance for understanding land effects on the mean climate.