A GLOBAL-MODEL OF THUNDERSTORM ELECTRICITY

An axisymmetric numerical model in an Earth-centered spherical coordin ate system is created to calculate the electric field distribution and current distribution from a thunderstorm source in the global electri cal circuit. The model includes a hemisphere in which the thunderstorm is located, an atmosphere and ionosphere with anisotropic height-vari able conductivities, and a passive magnetic conjugate hemisphere. Both single-cell thunderstorms and symmetric multicell thunderstorm comple xes can be modeled. The current output from the thunderstorm spreads o ut in the ionosphere and flows along the magnetic field lines into the conjugate hemisphere. Approximately half of the current that reaches the ionosphere flows into the conjugate hemisphere, and the rest is re directed to the fair-weather portion of the storm hemisphere. Two exam ples of this general model are discussed, a single-cell severe storm a nd a multicell severe storm. Results of this study show that it is imp ortant to include a realistic model of the ionosphere to evaluate the spread of current in the ionosphere and the mechanism of thunderstorm charging of the global electric circuit.