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Electric Atmosphere
Mon Oct 18, 2004
Listen in RealAudio 
When lightning strikes, we know a great flow of electrical energy has occurred. But
thunderstorms are not the only time electricity flows between the sky and the ground. In
fact, a fair-weather electrical current is flowing around you right now. Hi, I’m Bryan
Yeaton, and this is The Weather Notebook.
If you have ever been zapped by a typical 120-volt home outlet, you might be shocked to
know that during fair weather, a difference of from 200,000 to 500,000 volts exists
between the Earth’s surface and the high-altitude ionosphere.
But have no fear, despite the pun, this potential difference is about 2.5 volts per inch.
To put that into perspective, it takes a difference of 40,000 volts to overcome the
resistance of one-inch of air and produce a spark of static electricity.
In 1947, General Electric engineer John Anderson undertook an interesting
demonstration of the fair weather electrical potential. The Empire State Building is a
well grounded structure, and thus the whole building has the same potential as the
ground. Standing on a high floor, Anderson extended his arm from an open window.
The strong potential difference between the atmosphere at that height and his arm still
at ground potential made his finger tips glow from the potential-generated ionization, a
form of St Elmo’s fire.
The planetary electrical field, generated by the solar wind rushing through the
magnetosphere, and the ionospheric winds, causes a global, fair-weather electrical
current to flow from the upper atmosphere to the surface. To maintain this electrical
circuit’s balance, one to two thousand thunderstorms must be active at any given time
on the planet returning charge to the upper atmosphere.
Thanks to our contributing writer, meteorologist Keith Heidorn. The Weather Notebook
receives funding from Subaru of America, and is produced by the Mount Washington
Observatory. Thanks to Trish Anderton for putting our show together.
Today's Links
Soaking in Atmospheric Electricity
http://science.nasa.gov/newhome/headlines/essd15jun99_1.htm
Fair-weather Atmospheric Electricity
http://www.geo.fmi.fi/~tjt/fairw.html
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