A study of enhanced fair-weather electric fields occurring soon after sunrise

• Published in: Journal of Geophysical Research: Atmospheres 1999-10, Vol.104 (D20), p.24455-24469
• Main Authors: Marshall, Thomas C., Rust, W. David, Stolzenburg, Maribeth, Roeder, William P., Krehbiel, Paul R.
• Format: Article
• Language: English
• Subjects: Atmospheric electricity; Earth, ocean, space; Exact sciences and technology; External geophysics; Meteorology
• ISSN: 0148-0227; 2156-2202
• DOI: 10.1029/1999JD900418

In this paper we describe several series of electric field soundings made in the lowest few hundred meters above the ground on 6 days at Kennedy Space Center in Florida. These soundings are used to determine the charge density and thickness of the charged electrode layer just above the surface of the Earth both before and after sunrise during fair weather. On most of the days considered, there was an anomalous enhancement in the ground‐level electric field that was probably associated with the “sunrise effect” previously described by others. At our tether site we found that the electrode‐layer charge density began increasing at about the same time as the local enhancement in the electric field magnitude at the ground. Shortly before the peak in the local E enhancement, the electrode‐layer charge density decreased while the charge thickness increased; these changes were coincident with a decrease in relative humidity, a shift in the average wind direction, and increases in the fluctuations in relative humidity, wind speed, and wind direction. The typical decrease in charge density was from 0.2 to 0.05 nC m−3, while the charge layer thickness increased from less than 20 m to almost 200 m. Our measurements suggest that enhanced positive electrode layers accumulate before sunrise very close to the surface because there is relatively little radioactivity in the soil or air. Local, upward mixing of the denser, low‐lying, electrode‐layer charge may account for the observed sunrise enhancement in electric field. The larger enhancements observed at some sites may indicate that upward convection is supplemented by advection of denser charge from above water surfaces a few tens of meters (or less) from the measurement sites.