STRATOSPHERE-TROPOSPHERE EXCHANGE IN A MIDLATITUDE MESOSCALE CONVECTIVE COMPLEX .2. NUMERICAL SIMULATIONS

Mixing across the tropopause due to intense convective events may sign ificantly influence the atmospheric chemical balance. Stratosphere-tro posphere exchange acts as an important natural source of O-3 in the tr oposphere, and a source of H2O, HCs, CFCs, HCFCs, and reactive nitroge n in the stratosphere. The redistribution of atmospheric trace gases p roduces secondary radiative, dynamical and climate effects, influencin g lower stratospheric temperatures and the tropopause height. During t he 1989 North Dakota Thunderstorm Project, a severe storm which evolve d into a mesoscale convective complex (MCC) on June 28-29 showed the u nusual feature of an anvil formed well within the stratosphere and pro duced strong vertical mixing of atmospheric trace gases including H2O, CO O-3, and NOy as discussed by Poulida et al. [this issue] in Part 1 of this paper. In this paper the two-dimensional NASA Goddard Cumulus Ensemble (GCE) model was employed to simulate this convective storm u sing observed initial and boundary conditions. The sensitivity to the domain size, initial and boundary conditions, stability, and time reso lution are evaluated. Synoptic-scale moisture convergence, simulated b y moist boundary inflow, influences significantly the storm intensity, spatial structure, and trace gas transport, and produces a storm that reintensifies after the initial decay, mimicking the observed behavio r of the MCC. The deformation of the tropopause documented with aircra ft observations was qualitatively reproduced along with transport of s tratospheric ozone downward into the troposphere, and the transport of trace species from the boundary layer upward into the stratosphere. I f the chemistry and dynamics of this storm are typical of the roughly 100 MCCs occurring annually over midlatitudes, then this mechanism pla ys an important role in CO, NOy, and O-3 budgets and could be the domi nant source of H2O in the lower stratosphere and upper troposphere ove r midlatitudes.