The Time Scale of Shallow Convective Self‐Aggregation in Large‐Eddy Simulations Is Sensitive to Numerics

Abstract

Abstract Numerical simulations of the tropical mesoscales often exhibit a self‐reinforcing feedback between cumulus convection and shallow circulations, which leads to the self‐aggregation of clouds into large clusters. We investigate whether this basic feedback can be adequately captured by large‐eddy simulations (LESs). To do so, we simulate the non‐precipitating, cumulus‐topped boundary layer of the canonical “BOMEX” case over a range of numerical settings in two models. Since the energetic convective scales underpinning the self‐aggregation are only slightly larger than typical LES grid spacings, aggregation timescales do not converge even at rather high resolutions (<100 m). Therefore, high resolutions or improved sub‐filter scale models may be required to faithfully represent certain forms of trade‐wind mesoscale cloud patterns and self‐aggregating deep convection in large‐eddy and cloud‐resolving models, and to understand their significance relative to other processes that organize the tropical mesoscales.