Simulation of a Mature Mesoscale Convective System Using a Nonlinear Balance Model

Abstract

The authors have made a number of calculations with a nonlinear balance model to test the hypothesis that the mesoscale lifting observed in the mature phase of a mesoscale convective system (MCS) can be explained as a moist, quasi-balanced process. A potential vorticity distribution like that seen in a mature MCS is produced by imposing a heat source of realistic size and magnitude for 40 ks (approximately 11 h) on a sheared environment that is slightly stable to moist slantwise convection. The subsequent evolution of the system for another 40 ks is then computed assuming that updrafts ascend moist adiabatically. Diabatic cooling comes from the evaporation of precipitation failing out of updraft regions. Mass fluxes and rainfall rates in the second half of the simulation compare well with observed values. Energetically, the system simulated becomes more and more like a small, moist baroclinic disturbance with time. Latent heat release in the mesoscale updraft is essential to the simulated MCS's evolution.