Spectral Analysis of Tropical Disturbances Appearing in a GFDL General Circulation Model

Abstract

A space-time cross spectrum analysis is applied to the 11-layer, 2.4° mesh GFDL general circulation model with seasonal variation, extending the work of Manabe et al. A statistical study is made of the model's tropical disturbances during the period July through October with respect to their wave characteristics, three-dimensional structure, energetics, and their role in the general circulation. Four types of equatorial traveling waves are isolated from stationary waves and ultra-long waves extending from middle latitudes. They are identifiable with observed mixed Rossby-gravity waves (Yanai waves), Kelvin waves, equatorial Rossby-type waves, and easterly waves. All these traveling waves are maintained primarily by the conversion of available potential energy generated by condensational heating. This heat is associated with traveling rainfall disturbances localized, in particular, in the western Pacific of the northern summer hemisphere where the sea surface is relatively warm.