Are large high-altitude electric fields caused by global thunderstorms?

Using the model of a spherical symmetric atmosphere the large-scale electric fields generated by the global thunderstorms are investigated. Theoretical formulations have been developed to calculate high-altitude electric fields due to global thunderstorms, taking into account the presence of the ionosphere. We make use of the assumption that in the ionosphere the geomagnetic field lines are equipotentials. The calculations indicate that the solution is highly sensitive to the variation of this upper boundary condition.