Some Recent Key Aspects of the DC Global Electric Circuit

The DC global electric circuit, GEC, was conceived by C.T.R. Wilson more than a century ago. Powered by thunderstorms and electrified shower clouds, an electric current I similar to 1 kA flows up into the ionosphere, maintaining the ionospheric potential V similar to 250 kV with respect to the Earth's surface. The circuit is formed by the current I, flowing through the ionosphere all around the world, down through the atmosphere remote from the current sources (J similar to 2 pA/m(2) through a resistance R similar to 250 Omega), through the land and sea surface, and up to the thunderstorms as point discharge currents. This maintains a downward electric field E of magnitude similar to 130 V/m at the Earth's surface away from thunderstorms and a charge Q similar to-6.10(5) C on the Earth's surface. The theoretical modelling of ionospheric currents and the miniscule geomagnetic field perturbations (Delta B similar to 0.1 nT) which they cause, as derived by Denisenko and colleagues in recent years, are reviewed. The time constant of the GEC, tau = RC, where C is the capacitance of the global circuit capacitor, is estimated via three different methods to be similar to 7 to 12 min. The influence of stratus clouds in determining the value of tau is shown to be significant. Sudden excitations of the GEC by volcanic lightning in Iceland in 2011 and near the Tonga eruption in 2022 enable tau to be determined, from experimental observations, as similar to 10 min and 8 min, respectively. It has been suggested that seismic activity, or earthquake precursors, could produce large enough electric fields in the ionosphere to cause detectable effects, either by enhanced radon emission or by enhanced thermal emission from the earthquake region; a review of the quantitative estimates of these mechanisms shows that they are unlikely to produce sufficiently large effects to be detectable. Finally, some possible links between the topics discussed and human health are considered briefly.