Atmospheric electric conduction and convection currents near the earth's surface

Abstract

Fine weather ionic conduction and convection currents near the Earth's surface have been studied. Air-earth current density, potential gradient, electric space char^ density, number density of ions of either sign have been measured. It has been confirmed that raised earthed antennas can also be used for air-earth current measurements. Air-earth current measurements with a wire and a plate antenna, show- that within the first few metres of the atmosphere the transfer of electric space charge by moving air masses produces currents comparable to the conduction current. The term 'advection current' has been used to denote those currents produced by the horizontal movements of air masses containing electric space charge. An experiment performed in a low-speed wind tunnel shows that ions in moving air streams are not likely to be controlled by potential gradients less than 1000 V m" space charge measurements show pulses lasting about a-5minute. They usually lie between 10 and 20 pCm(^-3). A qualitative explanation is given by solving the continuity equation. A theoretical account of the movement of ions in the atmosphere is also given. Analysis of the measured parameters using a computer programme suggests the existence of a layer of positive space charge, a few millimetres thick, close to the Earth's surface. Occurrence of extensive air showers has been recorded to see if there is any unobserved relationship with atmospheric electric elements. Measurements did not show much evidence; however, these are by no means conclusive. Simple calculation shows that only showers corresponding to primary energies of 10(^19)eV or 10(^20) eV can give measurable changes in the air-earth current density. The difficulties of measuring separately the two components of the conduction current by the direct method at any point above the Earth's surface is also discussed.