Abstract
Employing an implicit representation scheme for cumulus convection (Yamasaki, 1986), numerical experiments are performed to study tropical cyclone formation in the intertropical convergence zone. Fine resolution grid of 40km is used in the tonal belt where the sea surface temperature is relatively high while two areas having a coarse grid resolution of 120km are located to the north and the south. Cyclic conditions are imposed in the tonal direction. Initially, buoyancy perturbations are added to a resting atmosphere or an easterly flow having a horizontal shear is applied so that vertical motion (and convection) may be initiated. No external disturbances such as subtropical highs are taken into account.
Results of the numerical experiments indicate that convection and larger-scale circulations such as tropical disturbances and meridional Hadley circulations interact in a cooperative way. As a result, they are maintained or formed repeatedly over a long period of time. Some weak disturbances or vortices which are created by convective activity develop to become tropical depressions and tropical cyclones. In many respects results obtained in this study are consistent with those from the model of explicit cumulus convection (Yamasaki, 1983, 84).
