Thursday, 2 August 2001
The influence of electrification on microphysical and dynamical processes inside thunderstorms
A new three-dimensional dynamics and electrification coupled model has been developed for investigating the influence of electrification on microphysical and dynamical processes inside thunderstorms. This model, modified from a three-dimensional, time-dependent cloud model, includes forty-two microphysical processes and five electrification mechanisms. Parameterization of intracloud discharge process is also included. The part of investigation in this work examines the comparison between the model results and the observations with respect to both electrical and microphysical aspects as well as dynamical aspect. The model appears to do a good job in reproducing many of the observed characteristics of thunderstorms. The electrical structure deduced from the model shows a general agreement with the observed. Effect of electrification on microphysical and dynamical processes are investigated by performing two different numerical experiments, one with electrification processes and the other without electrification processes. Simulations show that the mass of hydrometeors transferred in microphysical processes, especially to collection and coalescence processes, is considerably changed by electrification in thunderstorms as a result of significant modification of terminal fall speed of large precipitation particles. Change of the mass transferred in microphysics inevitably alters the buoyancy of the cloud by changing its water loading and increases latent heat release in the middle part of thunderstorms. Electrification processes, therefore, subsequently enhance the convection in the cloud to some limited extent. Reinforced updraft sustains large precipitation particles and prevents particles from falling out of cloud earlier. Consequently, either amount of solid precipitation or diameter of solid precipitation particles on the surface is increased.