Atmospheric Electric Measurements during the 1972 Eclipse over Nova Scotia

Abstract

An observing station was set up near Malignant Cove, Nova Scotia, close to the centre line of the 10 July 1972 eclipse. Measurements were made of positive and negative polar conductivity, air-earth current density, space charge density, potentials at 25 cm, 1 m, 2.5 m and 6 m in a vertical array and at 1 m with a fast response probe. Airborne measurements at constant altitude above the exchange layer were made of potential gradient. Also monitored were solar radiation, wind speed and direction.

Totality lasted about 2.5 minutes. The vertical probe array showed nearly simultaneous perturbations of potential dropping to a minimum of about 35% of normal fair weather potential 45 minutes after totality. The fast response probe showed a progressive attenuation of the higher frequency fluctuations during and after the eclipse and then a sudden reversion to the pre-eclipse noise spectrum about 25 minutes after totality. The measurements of conductivity, air-earth current density and space charge also showed interesting changes, some of which are consistent with an overall pattern of events. The airborne readings showed no clearly defined effects.

The area covered by the eclipse may be considered as a moving region of inhibited convection. Mixing dies away from the ground up. Ions move mostly under the influence of the electric field. Removal of the convective component results in an increased total current density bringing excess positive space charge to ground. Radioactive gas from the ground is trapped near the earth, producing a region of high ionization. The development of these phenomena and their behavior on the renewal of convection are used to explain the observed changes in atmospheric electric parameters.