A GENERAL FRAMEWORK FOR CONVECTIVE TRIGGER FUNCTIONS

A general framework for the trigger function used in convective parame terization routines in mesoscale models is proposed. The Framework is based on the diagnosis of the accessibility of potential buoyant energ y. Specifically, the trigger function 1) estimates the magnitude of th e largest vertical velocity perturbation from a source layer and 2) ca lculates the total amount of inhibition between the source layer and t he level of free convection. The calculation of perturbation magnitude accounts for such factors as subgrid-scale inhomogeneities, a convect ive boundary layer, and convergence within the source layer. Specific formulations to quantify these factors are proposed. The trigger is te sted in a simulation using the PSU-NCAR mesoscale model MM5. The event chosen for simulation is a summertime case exhibiting a variety of en vironments. The results of this simulation are compared with a simulat ion using the Fritsch-Chappell (FC) trigger function. It is found that decisions made by the new trigger function are more physically consis tent with the local environment than decisions made by the FC trigger.