GROUND-BASED INSTRUMENTATION FOR MEASUREMENTS OF ATMOSPHERIC CONDUCTION CURRENT AND ELECTRIC-FIELD AT THE SOUTH-POLE

We have constructed instruments to measure the atmospheric conduction current and the atmospheric electric field: two fundamental parameters of the global-electric circuit. The instruments were deployed at the Amundsen-Scott South Pole Station in January 1991 and are designed to operate continuously for up to one year without operator intervention. The atmospheric current is measured by a sensor that uses a split-hemispheric conducting shell of 17.8-cm radius, separated by a thin Teflon insulating disk. The detection electronics are inside the sphere. In principle, the atmospheric current flows into one hemisphere, through the electronics where it is measured, and out the other hemisphere. The electric field is measured by a field mill of the rotating dipole type. The electric field sensing elements are two 30-cm-long antennas, driven to rotate in the vertical plane at 1800 rotations per minute. Two arrays of identical instruments have been deployed, separated by 600 m, in order to distinguish between atmospheric electrical signals of local and global origin. The separation distance of the arrays was determined by the climatology of the Antarctic plateau. Sample data from the first days of operation at the South Pole indicate variations in the global circuit over time scales from minutes, to hours, to days.