Reproducibility of Equatorial Kelvin Waves in a Superparameterized MIROC: 1. Implementation and Verification of Blockwise-Coupled SP-MIROC

The potential scope of superparameterization (SP) was extended to higher resolutions of the global climate model (GCM) component by devising a technique called blockwise coupling. In this method, a horizontal average of multiple GCM columns, instead of one, is coupled to a cloud-resolving model (CRM) domain. This enables SP-GCMs to reduce the computational cost drastically, enabling higher-resolution GCMs to be superparameterized. A blockwise-coupled SP-GCM called SP-MIROC was implemented by coupling the climate model MIROC6 to the CRM SCALE-RM. The 4 × 4-bundled SP-MIROC successfully reproduced horizontal patterns and frequency distributions of precipitation and realistic amplitudes of equatorial Kelvin waves (EKWs), which were underestimated in the standard MIROC6. As discussed in Yamazaki and Miura (2024b, https://doi.org/10.1029/2023MS003837) of this study, the amplitude boost of EKWs was enabled by a top-heavy heating in SP-MIROC. Comparison of power spectra between the 4 × 4-bundled SP-MIROC and nonbundled SP-MIROC indicated that the effective resolution of dynamic variables was not degraded by the blockwise technique. Rather, spectra in the 4 × 4-bundled SP-MIROC were more realistic than those in the nonbundled SP-MIROC. Although the 4 × 4-bundling limits convective coupling in the smallest GCM scale, it could offer the best match of resolutions between the GCM-handled dynamics and SP-derived physics because the effective resolution of the dynamics is lower than the nominal grid spacing.