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

Content Provider	Springer Nature Link
Author	Rycroft, Michael J. Harrison, R. Giles Nicoll, Keri A. Mareev, Evgeny A.
Copyright Year	2008
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.Detailed measurements made near the Earth’s surface show that Ohm’s law relates the vertical electric field and current density to air conductivity. Stratospheric balloon measurements launched from Antarctica confirm that the downward current density is ∼1 pA m$^{−2}$ under fair weather conditions. Fortuitously, a Solar Energetic Particle (SEP) event arrived at Earth during one such balloon flight, changing the observed atmospheric conductivity and electric fields markedly. Recent modelling considers lightning discharge effects on the ionosphere’s electric potential (∼+250 kV with respect to the Earth’s surface) and hence on the fair weather potential gradient (typically ∼130 V m$^{−1}$ close to the Earth’s surface. We conclude that cloud-to-ground (CG) lightning discharges make only a small contribution to the ionospheric potential, and that sprites (namely, upward lightning above energetic thunderstorms) only affect the global circuit in a miniscule way. We also investigate the effects of mesoscale convective systems on the global circuit.
Starting Page	83
Ending Page	105
Page Count	23
File Format	PDF
ISSN	00386308
Journal	Space Science Reviews
Volume Number	137
Issue Number	1-4
e-ISSN	15729672
Language	English
Publisher	Springer Netherlands
Publisher Date	2008-05-24
Publisher Place	Dordrecht
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Atmospheric electric circuit Conductivity models Fair weather observations Electrostatic modelling Astrophysics Space Exploration and Astronautics Planetology Extraterrestrial Physics, Space Sciences
Content Type	Text
Resource Type	Article
Subject	Astronomy and Astrophysics Space and Planetary Science

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1	Ministry of Education (GoI), Department of Higher Education	Sanctioning Authority	https://www.education.gov.in/ict-initiatives
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