山崎一哉さんと三浦裕亮さんの論文２編がアメリカ地球物理学連合（AGU）の論文誌Journal of Advances in Modeling Earth Systemsに掲載されました

山崎一哉さんと三浦裕亮さんの論文２編（Part I, Part II）がアメリカ地球物理学連合（AGU）の論文誌Journal of Advances in Modeling Earth Systemsに掲載されました。

Part I

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

概要：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.

Part II

タイトル：Reproducibility of Equatorial Kelvin Waves in a Super-Parameterized MIROC: 2. Linear Stability Analysis of In-Model Kelvin Waves

概要：While low-resolution climate models at present struggle to appropriately simulate convectively coupled large-scale atmospheric disturbances such as equatorial Kelvin waves (EKWs), superparameterization helps better reproduce such phenomena. To evaluate such model differences based on physical mechanisms, a linearized theoretical framework of convectively coupled EKWs was developed in a form readily applicable to model evaluation by allowing background stability and diabatic heating to have arbitrary vertical profiles rather than assuming simplified ones. A system of linearized equations of convection-coupled gravity waves was derived as a two-dimensional model of the convectively coupled EKWs. In this work, the basic states are taken from observations, CTL-MIROC and SP-MIROC experiments introduced in Part 1. The tendency of convectively coupled gravity waves to grow faster under top-heavy heating is confirmed for realistic stratification profiles, as found in previous studies under constant stratifications. A comparison of linear unstable solutions with basic states taken from SP-MIROC and CTL-MIROC shows that the top-heavy heating profile in SP-MIROC largely contributes to the enhancement of the EKW-like unstable modes, while subtle differences of stratification profiles considerably affect EKW behaviors. The bottom-heavy heating bias in the CTL-MIROC likely originates from insufficient modeling of subgrid stratiform precipitation in tropical organized systems. It is desirable to incorporate such stratiform components in cumulus parameterizations to achieve better EKW reproducibility.