"The global atmospheric electrical circuit and climate", by R. G. Harrison of the Department of Meteorology at the University of Reading, appeared in Surveys in Geophysics 25 (2004). It is a review article covering two centuries of fair-weather atmospheric electricity, written mainly to ask whether changes in the planet's electrical circuit could affect clouds and climate. It never mentions Jules Guillot, his double-antenna collector or any scheme for drawing power from the sky. Its value to this dossier is different: it sets out, with typical values, how much voltage and how much current the fair-weather atmosphere actually carries, and how scientists have collected that electricity to measure it. Those are the quantities against which the 1920s claims for Guillot's apparatus can be judged.
What is the global circuit?
The review describes a planet-sized electrical loop. Thunderstorms and electrified shower clouds act as the generators, charging the lower ionosphere positive relative to the ground. Everywhere else, in fair-weather regions, a small current of ions leaks back down through the weakly conducting air. The idea goes back to C. T. R. Wilson in 1920 and 1929. According to the review, Wilson's theory, the 1935 Explorer II balloon measurement of stratospheric conductivity and the cruise data of the survey vessel Carnegie together shaped the twentieth-century picture of fair-weather electricity. The ship worked at sea, and Harrison points out why that mattered: air over the oceans is usually far from continental pollution, which makes it well suited to fair-weather measurement. Averaged over many fair days, the field there follows a daily cycle keyed to universal time rather than local time, peaking around 19:00 GMT in the review's table. That shared worldwide rhythm is what atmospheric scientists call the Carnegie curve, and the review links it to the daily swing in global thunderstorm area.
Air conducts at all only because cosmic rays, radon and ground radioactivity keep ionising it. Harrison notes that most of the atmosphere's resistance lies in the polluted boundary layer near the ground, where ions stick to aerosol particles.
The numbers
The review's table of typical fair-weather values is the core of its usefulness here:
- surface potential gradient: 120 V per metre (elsewhere the review gives about 150 V per metre at 1 m as typical, varying with site);
- vertical conduction current density: 3 pA per square metre;
- air conductivity at sea level: 20 fS per metre;
- ionospheric potential: 250 kV;
- total resistance of the atmosphere: 230 ohms;
- total air-Earth current: 1800 A (the text gives an estimate of 2000 A);
- columnar resistance of a one-square-metre column: 120 PΩ m².
The review adds that the ionosphere and Earth form a capacitor whose charge would drain in a time constant of about 10 minutes if generation stopped. The field persists only because storms keep recharging it.
How collectors have been used
For two centuries the standard way to read the atmosphere's potential has been a "collector" or potential probe. Harrison lists the variants: burning fuses, Kelvin's water dropper, radioactive sources and long horizontal wire antennas. He explains that all of them do the same job, lowering the effective resistance between the probe and the air, either by adding ions near the probe or, in the long-wire case, by enlarging the collecting area. A long-wire antenna is also cited as an effective way to measure the air-Earth current itself.
The review stresses the difficulty this involves. In its words, fair-weather signals appear "at high source impedance", so sensitive electrometers and excellent insulation are needed, and cobwebs and dirt must be cleaned off regularly. In this literature an antenna is an instrument for sensing a tiny current, not a power source.
What the review says about height and pollution
Two of the review's observations concern conditions any elevated collector would face, although the review itself does not discuss collecting devices of Guillot's kind. Balloon ascents around 1900 found the field generally weakens with height, even though the ionospheric potential above remains large. Readings near cities were dominated by smoke, which cuts conductivity: B. Chauveau's 1893 measurements at the foot and the top of the Eiffel Tower in Paris show quite different daily cycles, which the review attributes to polluted urban air.
Checking the 1920s figures against it
Two of the dossier's sources quote the global fair-weather current as 1,500 amperes: Andry-Bourgeois in 1923 and Robert A. Nelson, who also gives 3 x 10^-16 A per square centimetre, which equals 3 pA per square metre. Both are the same order as the review's 1800-2000 A and 3 pA per square metre. Neither the review nor the Guillot sources refers to the other; set side by side here, they simply give figures of the same order for the global current.
Simple arithmetic with the review's figures shows the scale. Multiplying its ionospheric potential by its total current gives roughly 450 megawatts for the whole planet's fair-weather circuit. At 3 pA per square metre, the downward current through one square kilometre is about 3 microamperes. This is a simple illustration, not a figure from the review. The dossier's figures for Guillot's apparatus do not map neatly onto it: the roughly 3 square metres in the Andry-Bourgeois article is the footprint of the ground installation, and the 15 to 20 metre mast (Andry-Bourgeois) and the antenna of about 20 metres (Nelson) are heights. No source gives the collector's effective collecting area, and the review does not discuss how much a large collector could deliver. Without those details, the review's figures give no basis for judging the 2.5–3 kW attributed to Guillot's collector in the 1930 encyclopedia account; setting the two side by side is an order-of-magnitude illustration only.
What the review does and does not establish
The review is a solid, referenced account of measured fair-weather values and of collector instruments built for measurement. It does not test any power-generating device, and it does not address storm-time collection, corona from point arrays, or the "siphon" mechanism Guillot proposed. It cannot show that his lamps did or did not light, and a reader comparing its fair-weather values with a claim of kilowatts from a single mast cannot settle the question from the review alone. The Guillot sources do offer mechanisms: Andry-Bourgeois describes the proposed "electric siphon", and Nelson says output depends on collector surface and antenna height. But these are unmeasured, untested explanations, and none of the sources gives a collecting area, load or duration for the claimed output. The kilowatt figure is asserted but undocumented, and it has not been independently measured or replicated.
Much of the paper deals with climate questions outside this dossier's scope: cosmic-ray effects on clouds, nuclear test fallout and long-term drift of the potential gradient. Harrison describes those links as largely unquantified.
Further reading
- Kelvin's 1859 Atmospheric Electricity Measurements: The Potential Gradient and the Water Dropper Equaliser (Aplin & Harrison) — Aplin and Harrison on Kelvin's calibrated potential-gradient measurements and the water dropper.
- Eclator — the output figures claimed for Guillot's collector.
Reference
R. G. Harrison, "The global atmospheric electrical circuit and climate", Surveys in Geophysics 25 (2004); preprint at https://arxiv.org/pdf/physics/0506077
Source notes & attribution
- https://arxiv.org/pdf/physics/0506077