The global circuit capacitor and two new ways of deriving the time constant of the global atmospheric electric circuit

Abstract

Temporal smoothing of the electrical impulses generated by lightning and shower clouds occurs through the global atmospheric electric circuit (GEC); smoothing is quantified by the time constant of the GEC. Two new methods for calculating this time constant are presented. They are based a) on a novel global circuit capacitor model, rather than the Earth-ionosphere capacitor model, and b) on the concept of dielectric relaxation time of near-surface poorly conducting air. The new GEC model considers the contributions of stratus clouds and their changes to the electrical conductivity of the air. Using model a), the time constants for the various regions of the atmosphere, over land and oceans, are obtained and the GEC time constant is found to be ∼10 min. This compares very favourably with the time constant derived from recent observations of the effects of sudden volcanic lightning on the GEC. The upper “pseudo-electrode” of the capacitor, the actual value of whose constant potential varies according to the conditions present, is found to be at an altitude of 1.8 km. For model b), the upper pseudo-electrode is placed at the boundary between dielectric and conducting atmospheres, i.e. where the displacement current equals the conduction current. Its altitude is 2.0 km, in the vicinity of stratiform clouds; the GEC time constant is 7.6 min. The vertical profile of air conductivity which best fits both DC GEC and AC (Schumann resonance) considerations is presented. Smoothing from the GEC's time constant provides steady background conditions for stratiform cloud edge charging which may affect their properties in the climate system; the steady conditions are also exploited biologically, e.g., by spiders and their webs. Other connections between atmospheric electricity and various living species are briefly explored.