New parameterization of non-inductive charge transfer based on previous laboratory experiments

Empirical equations for the sign and magnitude of the separated non-inductive charge during rebounding collisions of ice-crystal and graupel are obtained using discriminant and regression analyses. The original source of data is Takahashiʹs laboratory experiment [Takahashi, T., 1978. Riming electrification as a charge generation mechanism in thunderstorms. J. Atmos. Sci. 35. 1536–1548], who presented measured charge transfer values as isolines, function of cloud temperature and cloud water content. The simulations show that the use of these equations in a numerical cloud model gives similar values for the total charge density in a simulated thundercloud to those obtained using the lookup table of Takahashiʹs data as implemented by many authors. Tests reveal that the use of the proposed equations is computationally more efficient for numerical simulations of thunderstorm electrification comparing to the use of the look-up table. In addition, the results show that the different parameterization schemes for the charge transfer to a graupel particle due to a single ice crystal interaction proposed by Takahashi [Takahashi, T., 1984. Thunderstorm electrification — a numerical study. J. Atmos. Sci., 41. 2541–2558] and Saunders et al. [Saunders, C.P.R., Keith, W.D. and Mitzeva, R.P., 1991. The effect of liquid water on thunderstorm charging. J. Geophys. Res. 96. 11007–11017], may affect significantly the total charge density in the simulated cloud case.