In order to investigate the behavior of an ensemble of cloud clusters over a tropical ocean with the zonally uniform SST surrounded by the dry continent, numerical experiments have been conducted using a global spectral model. The long time-integrations were performed under the perpetual April SST conditions corresponding to the Northern Hemisphere spring to maintain the north-south symmetry of SST.
The following results have been obtained;
(1) On the equator cloud clusters tend to be located at the eastern end of moist region over the ocean (3000km westward from the eastern boundary). Thus, the location of cloud clusters on the equator is determined by the mutal interaction between cloud clusters and moisture fields. At the eastern boundary of the ocean, evaporation from the ocean is balanced with the westward advection of dry air. At the western boundary, meridional moisture transport also contributes to the moisture budget.
(2) In the subtropics cloud clusters tend to be located in the western part of the ocean. Time-average maximum of the precipitation exists 3000km-6000km off the western coast of the ocean. This is due to the fact that the moisture flux convergence is enhanced around the border between the ocean and the dry continent with no moisture supply. It implies that the dry continent influences the activity of cloud clusters over the ocean.