Charge density in the updraughts of thunderstorms: a numerical study in the frame of a Lagrangian model

A one-dimensional numerical model is used to study the charge density developed by the non-inductive crystal/graupel collision process along the path of rising thermals in convective clouds. The model employs the concept of successive thermals rising through the same volume with two regions identified: (i) an updraught simulated by successive ascending thermals and (ii) a non-active cloud mass formed from the debris of previously risen and stopped thermals. The microphysical processes utilise bulk parameterisation, while the charge transfer sign and magnitudes are based on laboratory studies. del results show multilayered charge distributions, the exact distribution being sensitive to updraught velocity and details of the cloud microphysics. The study demonstrates that the cloud particle collisional charge transfer mechanism is able to account for the detection of more than three vertically distributed cloud layers with alternating polarity, as noted by Stolzenburg et al. [J. Geophys. Res. 103 (1998) 14059; J. Geophys. Res. 103 (1998) 14079; J. Geophys. Res. 103 (1998) 14097] and others during balloon ascents through thunderstorms. The analysis also reveals that the data recorded during balloon ascents could be due in some clouds to the relative motion of the balloon with respect to the cloud updraught.