A quasi-static model of global atmospheric electricity, 1. The lower atmosphere


  • P. B. Hays,

  • R. G. Roble


A model of global atmospheric electricity is constructed and used to examine the electrical coupling between the earth's upper and lower atmospheric regions. The main sources of electric current within the model are thunderstorms, which are considered as dipolar electric generators with a net positive charge at the top of the thundercloud and a net negative charge at the bottom of the cloud. The thunderstorms are assumed to be distributed in geographic areas that are in accordance with the known statistical distribution of thunderstorm frequency at a given universal time. The electric potential at the surface of the earth is assumed to be zero along the earth's orographic surface. Calculations are made with and without the earth's orography. The electrical conductivity increases exponentially with altitude, and electrical effects are eventually coupled into the magnetosphere along geomagnetic field lines. Also, the electrical conductivity is assumed to vary with latitude, simulating the latitudinal variation of known cosmic ray production. The electrostatic model calculates the global distribution of electric potential and current for model conductivities and an assumed spatial distribution of thunderstorm current sources. The results show that large positive electric potentials are generated over thunderstorms and that these perturbations penetrate upward to ionospheric heights. The effect of a thunderstorm region in one hemisphere can be transmitted along geomagnetic field lines into the conjugate hemisphere; however, the potential perturbation in the conjugate hemisphere is damped below stratospheric altitudes. Electric fields over thunderstorm regions may approach 0.25–0.50 mV m−1 at ionospheric heights for nighttime conditions. The return current at the earth’s surface in the fair weather region is greater over mountainous regions than at sea level. The perturbation of the calculated electric potential and current distributions due to an increase in cosmic rays during a solar flare increase and the subsequent Forbush decrease in cosmic ray ionization is also discussed.