Electrification of stratiform regions in mesoscale convective systems. Part II: Two-dimensional numerical model simulations of a symmetric MCS

Model simulations of a symmetric mesoscale convective system (MCS; observat ions discussed in Part I) were conducted using a 2D, time-dependent numeric al model with bulk microphysics. A number of charging mechanisms were consi dered based on various laboratory studies. The simulations suggest that non inductive ice-ice charge transfer in the low liquid water content regime, c haracteristic of MCS stratiform regions, is sufficient to account for obser ved charge density magnitudes, and as much as 70% of the total charge in th e stratiform region. The remaining 30% is contributed by charge advection f rom the convective region. The strong role of in situ charging is consisten t with previous water budget studies, which indicate that roughly 70% of th e stratiform precipitation results from condensation in the mesoscale updra ft. Thus both in situ charging and charge advection (the two previously ide ntified hypotheses) appear to be important contributors to the electrical b udget of the stratiform region. The simulations also indicate that once the se charge densities are achieved, the sink of charge resulting from particl e fallout becomes approximately equal to the rate of charge generation. Thi s result is consistent with the quasi-steady layered structure that is comm only observed in these systems. Two noninductive charging parameterizations are rested and both are found to reproduce some of the observed stratiform charge structures. The evaporation-condensation charging and melting charg ing mechanisms are also investigated, but found to be insignificant.