| he AMIP simulation from 1979 to 1988 by the UIUC 7-layer tropospheric general circulation model (GCM), using observed sea surface temperatures, did not reproduce the well-organized, intraseasonal oscillations that are observed in the tropics. Because the simulations of the oscillations by many other GCMs also are deficient, we began an investigation of the possible cause and correction. For this investigation we raised the top of the 7-1ayer GCM from 200 mb to 50 mb and added 4 layers. We then focused our investigation with the resulting 11-layer GCM on the parameterization of cumulus convection. Three different convection parameterizations have been tested: (1) the UIUC GCM's original cumulus-convection parameterization, which includes a modified version of the Arakawa-Schubert (1974) penetrative-convection parameterization (AS) and a middle-level convection (MLC) parameterization; (2) the parameterization of Kuo (1974); and (3) the moist convective adjustment (MCA) parameterization of Manabe et al. (1965). For each parameterization, a relative-humidity criterion ;The diagnosis of our GCM simulations and our investigation using a one-dimensional model that is identical to the 11-layer UIUC GCM, except that all dynamical processes are ignored, have been carried out to explore explanations for the results based on existing theories. It is found that, among the mechanisms proposed in these theories, the nonlinear dependence of the condensational heating on the large-scale flow, and the phase lag between the heating and the moisture convergence, are responsible for the dependence of the simulated oscillation on... |
