A Quasi‐static model of global atmospheric electricity 2. Electrical coupling between the upper and lower atmosphere

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Abstract
A model of global atmospheric electricity is used to examine the influence of upper atmospheric generators, such as the ionospheric dynamo and the high‐latitude generator associated with magnetospheric convection, upon the global electrical circuit. The model for the lower atmosphere has been described in paper 1 (Hays and Roble, 1979). It includes the effects of orography, and it represents thunderstorms as dipole current generators randomly distributed in areas of known thunderstorm frequency. The electrical conductivity in the model increases exponentially with altitude, and electrical effects are coupled with a passive magnetosphere along geomagnetic field lines. The model determines the electric potential on the basis of an assumed spatial distribution of thunderstorm current sources. The large horizontal‐scale potential differences at ionospheric heights that are associated with the ionospheric dynamo and magnetospheric convection during geomagnetic quiet times, map effectively downward into the lower atmosphere, where perturbations of ±20% in the ground electric field and air‐earth currents at high latitudes are superimposed upon the diurnal variation that is established by worldwide thunderstorm activity. During geomagnetic storms and auroral substorms the perturbations are highly variable but are generally greater and occur futher equatorward. Any current imbalance caused by the superimposed ionospheric potential patterns requires a readjustment of the global fair weather potential difference between the ground and ionosphere to maintain the divergence of air‐earth current on a global scale equal to zero. Changes in upper atmospheric conductivity due to solar flares, polar cap absorptions, and Forbush decreases are shown to alter the downward mapping of the high‐latitude potential pattern and the global distribution of fields and currents.