Electrification of Stratiform Regions in Mesoscale Convective Systems. Part II: Two-Dimensional Numerical Model Simulations of a Symmetric MCS

Abstract

Model simulations of a symmetric mesoscale convective system (MCS; observations discussed in Part I) were conducted using a 2D, time-dependent numerical model with bulk microphysics. A number of charging mechanisms were considered based on various laboratory studies. The simulations suggest that noninductive ice?ice charge transfer in the low liquid water content regime, characteristic of MCS stratiform regions, is sufficient to account for observed charge density magnitudes, and as much as 70% of the total charge in the stratiform region. The remaining 30% is contributed by charge advection from the convective region. The strong role of in situ charging is consistent with previous water budget studies, which indicate that roughly 70% of the stratiform precipitation results from condensation in the mesoscale updraft. Thus both in situ charging and charge advection (the two previously identified hypotheses) appear to be important contributors to the electrical budget of the stratiform region. The simulations also indicate that once these charge densities are achieved, the sink of charge resulting from particle fallout becomes approximately equal to the rate of charge generation. This result is consistent with the quasi-steady layered structure that is commonly observed in these systems. Two noninductive charging parameterizations are tested and both are found to reproduce some of the observed stratiform charge structures. The evaporation?condensation charging and melting charging mechanisms are also investigated, but found to be insignificant.