Structure of Tropical Convective Systems in Aqua-Planet Experiments: Radiative-Convective Equilibrium Versus the Earth-Like Experiment

Abstract

A previous study shows that tropical convective systems share a similar structure regardless of horizontal scale: lower-level horizontal convergence precedes maximum precipitation and this convergence rises and tilts over time. We conduct a series of aqua-planet experiments (APE) using the Non-hydrostatic Icosahedral Atmospheric Model (NICAM) to investigate whether this structure is maintained under different conditions with an Earth-like APE (CTL-exp) and a radiative convective equilibrium (RCE-exp) where sea surface temperature is uniform and no planetary rotation is applied. The experiments are conducted with the 56 km mesh size with explicit convective calculation without a cumulus parameterization scheme. CTL-exp shows a well-known multi-scale convective structure where a smaller convective system propagates westward along the equator whereas a larger convective system propagates eastward. In RCE-exp, the simulation also has a multi-scale structure but the larger-scale convective system no longer propagates in a preferred direction. The convective systems in CTL-exp have a similar tilting structure to tropical convective systems regardless of horizontal scale, while the larger scale convective system in RCE-exp show a smaller tilting structure. We speculate that the difference in CTL-exp and RCE-exp structures comes from the propagation speed of the convective systems.