A new approach is taken to formulate a scheme of cumulus parameterization. The present　work represents a result of continuing effort to improve the hurricane intensity prediction, although it can be applied to numerical modeling of climate systems and mesoscale　dynamics if effects of convection are incorporated in the models through parameterization methods. The framework of the new scheme is presented.

In the proposed scheme, cumulus convection is initiated in a numerical model when thermodynamical state of the grid scale field, after the large-scale condensation, is unstable for a hypothetical cloud to develop with entrainment effect included. The fractional coverage of convection is determined.

It is assumed that convection consists of subcloud scale elements. Those elements　possess a mass of saturated updraft and the equal mass of sinking part containing　evaporating droplets. The vertical velocity, heat budget and moisture budget in upraft are determined to estimate ensemble effect of the elements on the　condensation process and the vertical transport of heat and moisture.

Substances in various phases formed following the condensation of water vapor will　be treated by a simple two-bin method.

Effects of convection are blended into the grid scale. In the proposed scheme, an adjusted or final target state of the grid scale is not presumed. In this sense, the scheme is prognostic.