Conductivity measurements near the ground

Abstract

Conductivity measurements in the lowest few metres of the atmosphere have been the subject of investigation of relatively few workers. Their results appear to be confusing especially where the electrode effect is concerned. The present work was undertaken as a further contribution to the understanding of conduction in the lowest metre of the atmosphere, simultaneous measurements of the polar conductivities of opposite sign at ground level as well as conductivities of either sign at 20 cm. and 100 cm. above the ground were made together with the potential gradient at ground level. A mean value for the wind speed, and the wind direction during a period of recording could be obtained from the records of the Durham University Observatory where the work was undertaken. The conductivities were measured using two cylindrical condensers of the Gerdien type housed in a pit underground with their intakes flush with the surface. Air from the required height was drawn through a cardboard tube of that height slipped over the outer tube of the Gerdien condenser. To minimise the distortion to the lines of force resulting from the introduction of the cardboard tube in this manner, the intake of the cardboard tube was surrounded by a narrow aluminium band continuously maintained at the right potential of the surroundings, by utilising the output of the field mill at ground and a "continuous balance circuit" of a Honeywell Brown recorder. Results have shown that both positive and negative conductivities decrease with height in the lowest metre from ground, due to the effect of the radioactivity of the soil. The variation of the radioactive emanation in the air is directly affected by the role which the wind plays in the mixing of the air. It is suggested that in post conditions overland these factors combine against the enhancement of the electrode effect.