Unstable and Damped Equatorial Modes in Simple Coupled Ocean-Atmosphere Models

Abstract

Abstract Free equatorial modes for several simple coupled ocean-atmosphere models are determined. They are found to include unstable and damped modes of large zonal scale and long period. The influence of ocean thermo-dynamics on unstable modal behavior is systematically explored. The Model I ocean features a local thermal equilibrium. In Model II, linearized temperature advection is the sole ocean thermal process. The Model III ocean features both advective and local thermal processes, while that of Model IV features only local thermal processes. The ocean and atmosphere are each represented by linear shallow water equations on the equatorial β-plane, and are linked by traditional couplings. A finite difference method with variable resolution is used to find eigenvalues and eigenvectors of the coupled systems. Key results are checked via a series method. Ocean modes are influenced most strongly by coupling, and are damped or destabilized depending on the configuration of induced atmospheric motion relati...