A fundamental problem in atmospheric electric research has been measurement of the intensity and variation of Earth's electric field, which is proportional to ionospheric potential (Vi). To obtain its magnitude an electric field sounding through the atmosphere is required. Data from the three programs that have measured Vi during the last half century were combined to determine the secular variation of global circuit intensity. The average geoelectric potential (Vi) magnitude has remained relatively constant at about 240 kV, except for a temporary increase of as much as 40% following a period of intense atmospheric nuclear testing in the early 1960s. Experiments were conducted to investigate the affect of temperature on Vi. Continental-scale hourly ground-level air temperature variation modulates the intensity of Vi and there is negative feedback involving cloud development that would stabilize temperature on the diurnal time scale. However, increased temperature-driven convection will increase water vapor in the troposphere and thus provide positive feedback enhancing global warming on longer time scales. Significant differences exist between the intensity of the DC global circuit and the diurnal and annual variations of global lightning frequency. The previously unknown minimum-to-maximum seasonal variation of Earth's electric field is about 15% of the mean with a maximum in late Northern Hemisphere summer and a minimum in winter.

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Airborne Research Associates, Weston, Massachusetts