National Academies Press: OpenBook

The Earth's Electrical Environment (1986)

Chapter: Fair-Weather Vertical Current Density and Total Current

« Previous: Electrical Conductivity, Columnar Resistance, and Global Resistance
Suggested Citation:"Fair-Weather Vertical Current Density and Total Current." National Research Council. 1986. The Earth's Electrical Environment. Washington, DC: The National Academies Press. doi: 10.17226/898.
Page 215

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THE GLOBAL ATMOSPHERIC-ELECTRICAL CIRCUIT 215 probably quite variable depending on variations of ionization rates, ion and neutral chemical reactions, aerosol and cloud interactions, and a host of other meteorological factors. The electrical columnar resistance that determines the local air-earth current flow and electric field is determined by the height integral of the reciprocal of the electrical conductivity distribution. The bulk of the columnar resistance resides in the troposphere, which can be strongly controlled by electrical conductivity variation owing to factors such as clouds, fog, aerosols, and pollution. Boeck (1976) showed that changes in the global conductivity may result in from 85Kr being released into the atmosphere. The low-frequency radiation from power lines (Vampola, 1977) may also affect the precipitation of electrons and consequently affect ionization in the stratosphere. The columnar resistance derived from the Gish formula is about 1.3 × 1017 Ω/m2. This fair-weather value probably varies considerably in place and time as determined by aerosol and weather conditions. The global variation of the columnar resistance is not well known, yet it is an important property of the global electrical circuit. The global resistance is the parallel circuit resistance obtained by adding the various columnar resistance values. Mühleisen (1977) estimated a global resistance of 230 Ω without mountains and 200 Ω when the Earth's orography is considered. The magnitude of the variability of global resistance is poorly known, and it is an important parameter that needs to be determined in order to improve our understanding of the Earth's global electrical circuit. Figure 15.6 Latitudinal distribution of the (a) vertical and (b) horizontal components of log10 σ (mhos/m), where s is the electrical conductivity (Tzur and Roble, 1983). Fair-Weather Vertical Current Density and Total Current The total current flowing in the global circuit is not well known, and only crude estimates have been made. Its value is generally estimated by integrating the measurable fair-weather vertical current density over the fair-weather area of the globe. A recent estimate by Mühleisen (1977) used 10–12 A/m2 for inhabited and industrialized areas, 2-4 × 10–12 A/m2 for vegetated ground and for deserts, 2.5 × 10–12 A/m2 over the Atlantic Ocean to derive a total global current of about 1000 A. About 750 A is derived for the current flow over oceans and 250 A for the current flow over the continents. Mühleisen (1977) pointed out that the columnar resistance over mountains is much smaller than over flat land near sea level, and he estimated that as much as 20 percent of the global vertical current streams toward mountains. Gathman and Anderson (1977) showed that the air-earth current also has a latitudinal variation due to the effect of the Earth's geomagnetic field on the cosmic-ray ionization rate throughout the troposphere. Another means of estimating the total current flow in the circuit is to estimate the total number of thunderstorms working simultaneously and multiply that value by the average current output determined from measurements over thunderstorms, as was discussed previously. Estimates of the number of global thunderstorms range from 1500 to 2000. If these numbers are multiplied by the average current output of thunderstorms (0.5 to 1.0 A), the total current is about 750 to 2000 A, which is nearly the same magnitude as the total current derived by air-earth current estimates, about 1000 A. Blanchard (1963) indicated that currents as large as hundreds of amperes flow from the ocean surface into the atmosphere as a result of electrified droplets that are ejected from the bursting of small bubbles. It also should be mentioned that intense electrification is associated with some volcanic eruptions. When such phenomena occur, they may have a significant input into the global electrical circuit. There is considerable uncertainty with these estimates that needs to be resolved. It is un

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This latest addition to the Studies in Geophysics series explores in scientific detail the phenomenon of lightning, cloud, and thunderstorm electricity, and global and regional electrical processes. Consisting of 16 papers by outstanding experts in a number of fields, this volume compiles and reviews many recent advances in such research areas as meteorology, chemistry, electrical engineering, and physics and projects how new knowledge could be applied to benefit mankind.

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