The Use of Large-Scale Budgets for Convective Parameterization

Abstract

Synoptic-scale mass and moisture budgets are objectively computed by kinematic techniques and compared to the mass and moisture budgets of a tornado-producing Oklahoma squall line. The rate of consumption of water vapor by the squall line is found to be significantly larger than the synoptic-scale moisture convergence; similarly, the mass processed by the squall line exceeds the synoptic-scale budget. This implies that additional vertical circulations must exist on a scale smaller than synoptic, probably a reflection of organized convective lifting and compensating downdrafts. Consequently, parameterization of mid-latitude organized convection, using synoptic-scale mass or moisture convergence to estimate cloud fluxes, will likely underestimate the amount of convective precipitation, the total vertical mass exchange and, therefore, the magnitudes of the thermodynamic stabilization and vertical momentum exchange as well.