An Overview of Earth’s Global Electric Circuit and Atmospheric Conductivity

Abstract

The Earth's global atmospheric electric circuit depends on the upper and lower atmospheric boundaries formed by the ionosphere and the planetary surface. Thunderstorms and electrified rain clouds drive a DC current (∼1 kA) around the circuit, with the current carried by molecular cluster ions; lightning phenomena drive the AC global circuit. The Earth's near-surface conductivity ranges from 10 −7 S m −1 (for poorly conducting rocks) to 10 −2 S m −1 (for clay or wet limestone), with a mean value of 3.2 S m −1 for the ocean. Air conductivity inside a thundercloud, and in fair weather regions, depends on location (especially geomagnetic latitude), aerosol pollution and height, and varies from ∼10 −14 S m −1 just above the surface to 10 −7 S m −1 in the ionosphere at ∼80 km altitude. Ionospheric conductivity is a tensor quantity due to the geomagnetic field, and is determined by parameters such as electron density and electron-neutral particle collision frequency. In the current source regions, point discharge (coronal) currents play an important role below electrified clouds; the solar wind-magnetosphere dynamo and the unipolar dynamo due to the terrestrial rotating dipole moment also apply atmospheric potential differences. M.J. Rycroft ( ) CAESAR Consultancy,

A Review of Low Frequency Electromagnetic Wave Phenomena Related to Tropospheric-Ionospheric Coupling Mechanisms

“…Differentiation between AC and DC electric circuits response is determined from the relaxation time of the system, i.e., when either conduction or displacement current processes are dominant (Greifinger and Greifinger, 1978). The main characteristics of the global circuit include: (i) near-surface conductivity from ~10 -6 Sm -1 for low contaminated ice and dry, poorly conducting rocks to ~10 -2 Sm -1 for clay or wet limestone and ~1 Sm -1 for sea water; (ii) ionospheric conductivity ~10 -6 Sm -1 in the D-region; (iii) vertical DC electric field varying between ~100 Vm -1 near the surface and a very small fraction of 1 Vm -1 at 80 km (changing significantly with latitude and day-night dichotomy); (iv) upward currents predominantly originating from thunderstorms; (v) fair weather downward current density ~1 pAm -2 ; (vi) and a 200-300 kV potential difference between the ionosphere and the surface (e.g., Bering et al, 1998;Rycroft et al, 2008). Thunderstorm activity and associated phenomena drive a DC current of ~1 kA, and each negative and positive lightning stroke carries an average AC current of ~30 and ~300 kA in the circuit, respectively, in less than 0.1 ms. Singh et al (2005) present an extensive, documented table with physical parameters of the global electric circuit.…”

Solar Influence on Global and Regional Climates

“…However, the expansion of the shielding solar magnetic field into interplanetary space results in the Sun modulating the number of GCRs reaching Earth (see, for example, review by Potgieter 2008). Air ions generated by GCRs enable Earth's global electric (thunderstorm) circuit (Rycroft et al 2008), and it has been proposed that they also modulate the formation of low-altitude clouds (Svensmark and Friis-Christensen 1997). The Sun also emits a continuous stream of low-energy charged particles called the solar wind (e.g., Marsch 2006).…”

Atmospheric Electrification in Dusty, Reactive Gases in the Solar System and Beyond

“…This provides an indication of how active (in terms of the rate of charge separation) a charging process needs to be at different heights in the atmosphere. In comparison with lower troposphere air with a typical conductivity of % 10 À14 S m À1 as reviewed by Rycroft et al (2008), the planetary surface has a greater electrical conductivity, of at least 10 À8 S m À1 . This means the air represents a low-conductivity region sandwiched between upper and lower boundaries having much greater conductivity.…”