Abstract
In a series of numerical experiments using a simplified, domain-averaged, coupled air-sea model, some aspects of the low-latitude large-scale interaction between the atmosphere and the ocean are investigated. Experiments are designed with a view toward elucidating basic mechanisms involved in the coupled processes. In this paper, we focus on the response of coupled system to 1) steady forcing, 2) seasonal variations and 3) large perturbations and continuous short-period random forcings.
Results indicated that the sea surface temperature (SST) distribution, which is strongly controlled by the oceanic upwelling, is the primary factor in determining the location and transition of the tropical rainbelt. The strongest convective activities in the ITCZ, however, depend mainly on the moisture supply from horizontal convergence and the static stability of lower atmosphere, and do not necessarily coincide with the occurrence of maximum SST. It is also demonstrated that the positive feedback processes between latent heat release in the ITCZ convection and the Hadley cell are opposed by oceanic upwelling and the concomitant cooling of the mixed layer through a stabilization of the lower atmosphere and a decrease of moisture supply from the tropical oceans. Further, results of the forced oscillation experiment suggest that the statistical effect of a large number of short-term atmospheric disturbances is capable of generating large-scale low-frequency variabilities in the coupled system. The separation in time scale is possibly the manifestation of a red-shifted spectral response in a multi-time-scale coupled climate system.
