[A-AS03] Large-scale moisture and organized cloud systems

[AAS03-P01] Reexamining the coarser-resolution regime boundary of convective self-aggregation in the radiative-convective equilibrium system

*Keiichi Hashimoto¹, Ching-Shu Hung¹, Hiroaki Miura¹ (1.The University of Tokyo)

Keywords:convective self-aggregation, radiative-convective equilibrium, SCALE-RM

Convective self-aggregation (CSA) observed in radiative-convective equilibrium (RCE) simulations is known to depend on the horizontal grid spacing and the horizontal domain size. Yanase et al. (2020) updated the "RCE Regime Diagram" of Muller and Held (2012) for a wide range of grid spacings and domain sizes and categorized the regime boundary line into three types: I, II, and III. Hung and Miura (2021) performed an ensemble experiment near the line II with the grid spacing of 2 km and the domain size of 384 km by 384 km and reported that the behavior of the system seemed stochastic. In this study, we investigate the behavior of the system when the grid spacing is 4 km. The domain size was increased from a square with a side of 100 km to that of 500 km. In all of the cases, the RCE system commonly shifted to a CSA state in about 20 days after the initiation of the simulation, and then, counterintuitively returned to a scattered state. In the simulations where the CSA was maintained for a longer period, the structures of wavenumber one only in one spatial direction were more stable, and the standard deviation of precipitable water and the characteristic length scale were kept constant for a longer time. The process of disaggregation was examined in detail for a simulation with a domain size of 200 km by 200 km. The transition to a scattered state appeared to be caused by the inflow of water vapor near the surface into the region of a dry patch.