Global electric circuit implications of combined aircraft storm electric current measurements and satellite-based diurnal lightning statistics

Abstract

[1] We have combined analyses of high-altitude aircraft observations of electrified clouds with diurnal lightning statistics from the Lightning Imaging Sensor (LIS) and Optical Transient Detector (OTD) that are carried aboard low-Earth-orbiting satellites to reproduce the diurnal variation in the global electric circuit. Using basic assumptions about the mean storm currents as a function of flash rate and location (i.e., land or ocean) and the global electric circuit, our estimate of the current in the global electric circuit matches the Carnegie curve diurnal variation to within 4% for all but two short periods of time, in which the difference was 11% in one time period (0430 UTC) and 6% in the second period (1830 UTC). This excellent agreement with the Carnegie curve was obtained without any tuning or adjustment of the satellite or aircraft data. We assume that (1) the mean values for current and flash rates in the aircraft storm overflight data set (1.7 A and 0.8 flashes min −1 for oceanic thunderstorms, 1.0 A and 2.2 flashes min −1 for land thunderstorms, 0.41 A for oceanic electrified shower clouds (i.e., electrified but no lightning detected), and 0.13 A for land electrified shower clouds) and (2) the diurnal variations in lightning rates over land and ocean found in the satellite data set are universally applicable. Mean contributions to the global electric circuit from land and ocean thunderstorms are 1.1 kA (land) and 0.7 kA (ocean). Contributions to the global electric circuit from electrified shower clouds are 0.22 kA for ocean storms and 0.04 kA for land storms. The mean total conduction current for the global electric circuit is 2.0 kA. The means that for the number of storms contributing to the global electric circuit, 1100 are land storms with lightning, 530 are ocean storms without lightning, 390 are ocean storms with lightning, and 330 are land storms without lightning. A closer fit to the Carnegie curve is possible if the contributions from electrified shower clouds are increased by a factor of 3 or 4.Citation: Mach, D. M., R. J. Blakeslee, and M. G. Bateman (2011), Global electric circuit implications of combined aircraft storm electric current measurements and satellite-based diurnal lightning statistics,

Measurements of Atmospheric Electricity Aloft

“…This led to an estimate that thunderstorms contribute 90%, and electrified clouds contribute 10% to current flow in the GEC. Mach et al (2011) also observed large differences between land and ocean storms, with land storms generating greater lightning rates, but smaller mean conduction currents than ocean storms. Thus most of the observed amplitude variation of the Carnegie curve can be accounted for by correctly including the differences that exist in the mean currents and flash rates between land and ocean thunderstorms.…”

“…Mach et al (2011) concluded that the mean total conduction current is 2.0 kA, where contributions to the GEC from land and ocean thunderstorms are 1.1 kA and 0.7 kA, respectively, and electrified shower clouds contribute 0.04 kA and 0.22 kA for land and ocean storms, respectively. Measurements such as these are essential to our understanding of the GEC and will aid in the development of future GEC models.…”

“…The aircraft measurements of Mach et al (2011) have also provided insight into an issue that has long perplexed atmospheric electricians -the difference in amplitude between the Carnegie curve and lightning activity. Although the phase of the diurnal variation in fair weather PG (known as the Carnegie curve -see section 2.2) matches well with the diurnal variation in lightning activity, discrepancies exist between the variation in amplitudes of the two curves (Carnegie curve varies by ≈15% whilst lightning flash rate varies by ≈35% about its mean) (e.g.…”

“…The reason for this is thought to be the contribution of electrified shower clouds (which do not produce lightning) to the GEC. Recent measurements by Mach et al (2011) have for the first time characterised the upward current flow from electrified shower clouds, which are found to produce 1/4 to 1/8 th of the current per cloud as storms with lightning. This led to an estimate that thunderstorms contribute 90%, and electrified clouds contribute 10% to current flow in the GEC.…”

The cloud chamber and CTR Wilson's legacy to atmospheric science

“…He even deployed his childhood microscope for thunderstorm electricity measurements (Wilson, 1960). Evidence of the success of the Wilson apparatus lies in its longevity, as it was used in an almost identical manner until 1979 at Kew Observatory, having been moved to an underground laboratory in 1931 (Harrison and Ingram, 2005). Beyond its original scientific application, data from the Wilson apparatus has proved suitable for reconstructing historic air pollution data (Harrison, 2006).…”