A. A. Few

An Unusual Lightning Flash at Kennedy Space Center

A lightning flash that struck the 150-meter weather tower at Kennedy Space Center was studied by several research groups using varioul techniques. The flash had unusually large peak currents and a stepped leader of relatively short duration. The charged regions neutralized by the three return strokes were located within a horizontal layer between heights of about 6 and 8 kilometers, where environmental temperatures were about –10� to –20�C. The charge source for the first return stroke coincided with a vertical shaft of precipitation inferred to have been graupel or hail. Charge sources for subsequent strokes were near the edge of the detectable precipitation echo. The overall channel length was about 10 kilometers. A Vertically oriented intracloud discharge occurred after the three return strokes.

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.

Advances in a Decade of Thunder Research

Techniques have been developed during the past decade that use the analysis of thunder for the investigation of lightning processes. Because the thunder signal propagates through the cloud without significant loss of information, these acoustic techniques will be as important to the study of intracloud lightning as photography has been to the study of the visible lightning.