On the Benefits of Tower-mounted Measurement of Near-surface Quasistatic Electric Fields

Measurements and analyses of atmospheric electric fields in the frequency range of DC to a few Hz are employed in earth and atmospheric sciences to evaluate cloud electrification, thunderstorm evolution, near-surface sources of charge production and separation, and the global electric circuit (GEC). Most operational and research uses of these data are limited by the difficulty in obtaining measurements that are minimally impacted by nearby low-mobility electrically charged particles (space charge) and near-surface radioactive sources. One such operational use is by US-based space launch facilities in order to avoid lightning strikes to a launch vehicle during ascent. Ground-based electric field measurements are a key part of these rules, with assessments being limited by nearby “noise sources”. Additionally, GEC research is seriously hampered by the difficulty in obtaining low-noise measurements of the fair-weather electric field for individual days. In this work, we discuss our efforts to improve atmospheric electric field observations by placing an electric field mill (EFM) atop a 90 m tower, compensating for the field enhancement produced by this mounting geometry, and comparing its calibrated field measurements to those measured at three nearby ground-mounted EFMs at Kennedy Space Center. The tower installation exhibited only benefits, relative to nearby surface-mounted sites, in the form of reduced sensitivity to wind and near-surface space charge sources, reduced influence of the “sunrise effect”, reduced sensitivity to charged precipitation during warm rain, and insensitivity to nearby vegetation growth. Measurements of electric fields produced by nearby thunderstorms were not compromised by this tower-mounted configuration.