Abstract
The global atmospheric electric circuit, which links the space environment with terrestrial weather, has mostly been investigated using fair-weather surface atmospheric electricity measurements. Retrieving global circuit information, however, requires the selection of “fair weather” data, to avoid local meteorological disturbances. The research results presented here challenge the applicability of long-standing definitions of electrically fair weather atmospheric conditions. From detailed new measurements and theory, three improved requirements (FW1 to FW3) for fair weather atmospheric electricity conditions are described. These are: (FW1) absence of hydrometeors, aerosol and haze, as apparent through the visual range exceeding 2 km, (FW2) negligible cumuliform cloud and no extensive stratus cloud with cloud base below 1500 m, and (FW3) surface wind speed between 1 m s−1 and 8 m s−1. Automatic and manual measurement approaches to identifying these requirements are given. Through applying these criteria at the many measurements sites now operating, the noise from meteorological variability will be reduced, leading to data more representative of the global electric circuit.
Highlights
IntroductionTypically those of the vertical electric field and the vertical current density have been made during the past 150 years, and are often undertaken to obtain information on the global atmospheric electric circuit
Surface atmospheric electricity measurements, typically those of the vertical electric field and the vertical current density have been made during the past 150 years, and are often undertaken to obtain information on the global atmospheric electric circuit
The GLOCAEM (GLObal Coordination of Atmospheric Electricity Measurements) project1 is intended to bring together many of the disparate sets of near surface atmospheric electricity measurements, as the lack of such data has been a major limitation for research in fair weather atmospheric electricity
Summary
Typically those of the vertical electric field and the vertical current density have been made during the past 150 years, and are often undertaken to obtain information on the global atmospheric electric circuit. Some global circuit quantities are less sensitive to local effects than others, such as the positive potential at about 10 km above the surface (Markson, 2007). 2 For a vertical component of the electric field Ez, the potential gradient F is given by F = -Ez This sign convention is adopted so that, in locally undisturbed (fair weather) atmospheric electrical conditions, F is positive. Before considering the perturbing effect of local conditions, it is important to point out that the absolute value of PG from a field mill, radioactive probe or Kelvin water dropper is affected both by the physical environment around the sensor as well as by the calibration of the sensor itself.
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