1. Reproducibility of Equatorial Kelvin Waves in a Super‐Parameterized MIROC: 2. Linear Stability Analysis of In‐Model Kelvin Waves.
- Author
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Yamazaki, K. and Miura, H.
- Subjects
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OCEAN waves , *CLIMATE change models , *LINEAR statistical models , *GRAVITY waves , *TWO-dimensional models - Abstract
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. Plain Language Summary: Present global climate models (GCMs) cannot resolve small‐scale cumulus convection. Hence, they cannot reproduce sufficient amplitudes of convectively coupled large‐scale atmospheric disturbances such as the equatorial Kelvin wave (EKW). In contrast, high‐resolution models that explicitly simulate cumulus convection can reproduce these disturbances better. In this study, a linearized theoretical framework of the convectively coupled EKW was developed to interpret and evaluate model behavior. Using this framework, EKWs simulated by different models were compared based on their physical mechanisms. The basic states were taken from observations and MIROC simulations introduced in Part 1. The tendency of EKWs to grow under a top‐heavy heating condition was confirmed under realistic stratification profiles as found in previous studies under constant stratifications. A comparison of linear unstable solutions with the basic states taken from the MIROC simulations showed that the heating altitude is the most important factor for enhancing the EKW‐like unstable modes, while stratification profiles can sometimes considerably affect EKW growth. Bottom‐heavy heating bias in the conventional MIROC likely originates from insufficient parameterization of organized precipitating systems in the tropics. It is desirable to incorporate such stratiform components in the cumulus parameterization to achieve better EKW reproducibility. Key Points: A linearized model of the EKW is derived in a form readily applicable to evaluation of numerical simulationsSuperparameterized MIROC enhanced EKW amplitudes through top‐heavy heating profilesTo improve EKW reproducibility, GCMs need better representation of tropical stratiform precipitation [ABSTRACT FROM AUTHOR]
- Published
- 2024
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