Contributions of different land and ocean regions to the diurnal variation of the global electric circuit are simulated using the Weather Research and Forecasting model by estimating the ionospheric potential produced by thunderstorms and electrified shower clouds in each grid column. The model predicts that contributions from land regions have maxima at about 14:00–18:00 local time (LT), whereas contributions from oceans have maxima at about 2:00–6:00 LT, and different ocean regions show nearly the same relative diurnal variation. It is remarkable that contributions from ocean regions with many islands (Maritime Continent and Middle America) have maxima at both 14:00–18:00 and 2:00–6:00 LT.
Theoretical estimation of the influence of large-scale conductivity inhomogeneities on the global electric circuit and, in particular, on the ionospheric potential is considered. A well-posed formulation of this problem is presented, on the basis of which an approximate method is developed so as to take account of large-scale conductivity inhomogeneities. Under certain restrictions imposed on the distributions of the conductivity and the external current density, explicit approximate formulas for the ionospheric potential are derived. The approximation developed is shown to be equivalent to that of classical models of atmospheric electricity in which the atmosphere is divided into two or more columns and is replaced by a simple equivalent electric circuit. The effect of conductivity inhomogeneities located inside and outside thunderclouds is discussed and, in particular, it is demonstrated that taking account of the conductivity reduction inside thunderclouds leads to a substantial increase in the ionospheric potential. The results following from the approximate theory are compared with those obtained from direct numerical simulations. It is found that the suggested approximation qualitatively accounts for the dependence of the ionospheric potential on the parameters of the conductivity distribution, although the relative error may be significant, especially in the case of a substantial reduction in the conductivity inside thunderclouds.
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