Comment on “Hy‐wire measurements of atmospheric potential” by R. H. Holzworth

Abstract

Measurement of the temporal variation of the global electrical circuit is becoming of increasing interest to the scientific community. Holzworth (1983) suggests that a tethered balloon at about 500 m over Wallops Island may have recorded variations of the global electrical circuit. This note discussed the general problem of how meteorological processes in the lower atmosphere control the variation of atmospheric potential and thus mask the global signal. It is shown that the reported tethered balloon potential measurements occurred (1) when changes in aerosol number density spectrum would have been expected and (2) when changes in convection may have occurred. These meteorological processes modulate the atmospheric electric field intensity locally. There is no correlation when the curve determined by the UT hourly average of the tethered balloon potentials is correlated with the hourly UT variation of the global circuit as represented by the Carnegie curve. For the abrupt drops in potential that occurred coincident with the breakup of fog or discontinuation of the morning rise in temperature to be due to changes in the global circuit would require more than 50% of the several thousand global thunderstorms to stop abruptly; this is unlikely. Because of the occurrence of fog and convection of hazy air rich in space charge, a coastal region is particularly inappropriate for attempts to measure the global circuit variation. Aside from problems related to location, the excessive voltages reported in the tethered balloon data suggest some problem with the measuring technique itself. These data give potentials at 530 m which are 48% higher than comparable aircraft measurements. Extrapolated to the ionosphere, the tethered balloon potential profiles would generally give ionospheric potentials on the order of 500 kV, which is well beyond the values measured in any other program. Holzworth [1981aHolzworth [ , 1981bHolzworth [ , 1982Holzworth [ , 1984 The factors that cause atmospheric electrical noise come together in such a way as to make a coastal region particularly unsuitable for global circuit measurements. In air masses within a few degrees of saturation there are large abrupt changes in the aerosol number density spectrum which alter conductivity and thus potential gradient. The increase in electric field intensity before the formation of fog--when the temperature-dew point spread becomes small--as well as the decrease in electric field intensity when the temperature-dew 2629

Measurements of Atmospheric Electricity Aloft

“…The maximum potential measured by Willett and Rust (1981) was 195kV, at a height of 5.3km above mean sea level, and 170kV at a height of 0.55km by Holzworth et al (1981). Concerns about the validity of the measurements by Holzworth et al (1981) were expressed by Markson (1984), who pointed out that the potential measurements were unusually large compared to previous aircraft measurements at the same height. Although the tethered balloon technique of measuring V I generally permits higher time resolution measurements than aircraft or free balloon platform, several problems are commonly encountered, including engineering difficulties associated with a 1km long tethered cable, the error incurred by extrapolation to ≈ 65km of the potential measurement from low altitudes, and the influence of local meteorological conditions on the atmospheric electrical parameters, in particular convection currents and aerosol concentration.…”