Sensitivity of the Horizontal Scale of Convective Self-Aggregation to Sea Surface Temperature in Radiative Convective Equilibrium Experiments Using a Global Nonhydrostatic Model

Abstract

We conduct radiative convection equilibrium experiments using a global nonhydrostatic model to investigate the dependence of convective self-aggregation (CSA) on domain size and sea surface temperature (SST). We use a spherical domain with radii varying from 1 to 1/16 of Earth's radius, as well as SSTs between 290 and 310 K. A single aggregation occurs at small domain sizes, whereas multiple aggregations emerge at sufficiently large domain sizes. Domain-averaged atmospheric temperature and humidity gradually increase with domain size until they reach convergence in cases of multiple aggregations. As domain size increases, surface wind speed increases, and the boundary layer becomes more humid. Because the radiative cooling in the free atmosphere also converges in cases of multiple aggregations, the surface evaporation must be limited due to the constraint of the energy balance. Thus, the convective region shifts from single to multiple aggregations to avoid increasing the surface wind speed. Our results show that the dependence of the horizontal scale of CSA on SST is not monotonic. This dependency is closely related to changes in the structure of the detrainment from the convective region at the melting level, resulting in enhanced radiative cooling at the top of the boundary layer near the convective region for cooler and warmer SSTs. This change in the circulation structure leads to increased surface wind speed with increasing domain size. This process affects the non-monotonic dependence of the horizontal scale of CSA on SST.