Simple Model Prediction of Horizontal Temperature Fields in the Subtropical–Subpolar System Caused by Sudden Change in Wind Stress Curl

Abstract

Abstract A four-level numerical model, which is driven by wind stress and surface heat flux, is used to study responses of horizontal temperature fields in the subtropical–subpolar system to a sudden change in the magnitude of the wind stress curl. Weakly nonlinear responses to O(1) change in the wind stress curl are examined, according to the effects on the Ekman pumping, convection, westward baroclinic wave, and advection. For this purpose, a quasi-analytical method, that is, characteristics associated with effects of both wave propagation and advection, is constructed based on a planetary geostrophic model with four-level geometry. Characteristics obtained for the first and second baroclinic modes are used to diagnose steady-state and time-dependent solutions. One feature of time-dependent motions predicted by the model is a westward propagation of the first baroclinic mode with a significantly higher speed than the combined speed of the nondispersive first-mode baroclinic Rossby wave and barotropic ci...