SIMULATION OF A MATURE MESOSCALE CONVECTIVE SYSTEM USING A NONLINEAR BALANCE MODEL

The authors have made a number of calculations with a nonlinear balanc e model to test the hypothesis that the mesoscale lifting observed in the mature phase of a mesoscale convective system (MCS) can be explain ed as a moist, quasi-balanced process. A potential vorticity distribut ion like that seen in a mature MCS is produced by imposing a heat sour ce of realistic size and magnitude for 40 ks (approximately 11 h) on a sheared environment that is slightly stable to moist slantwise convec tion. 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 falling out of upd raft regions. Mass fluxes and rainfall rates in the second half of the simulation compare well with observed values. Energetically, the syst em simulated becomes more and more like a small, moist baroclinic dist urbance with time. Latent heat release in the mesoscale updraft is ess ential to the simulated MCS's evolution.