Parameterization of thunderstorm charging including the cloud saturation effect

The effect of supersaturation on charge density in the updraft of a simulated thunderstorm is tested. Based on theoretical and statistical analyses, a parameterization of the effect of cloud saturation on the charge sign reversal line is proposed. Numerical simulations of three cloud cases with a 1D-cloud model show that the effect of the saturation ratio on the simulated cloud charge structure is strongly dependent on the cloud microphysics and dynamics. The inclusion of the saturation effect on the charge sign reversal line in the updraft of thunderstorms in general leads to an extension of the positively charged region at the expense of the negatively charged one. The effect is more pronounced in clouds with higher maximum updraft velocity and higher ice particle (crystals and graupel) content that are located in the cloud region with conditions close to those of the charge sign reversal line. In clouds with warmer cloud base, the inclusion of the saturation effect in the determination of the charge sign reversal line can lead to a considerable change of the updraft charge structure.