Fortunately, the voltage is modest and the current is almost nothing, so the effect is almost impossible to measure. The discovery of the fair weather circuit followed Ben Franklin's demonstration that lightning is caused by electricity. Later experimenters showed that clear, calm air carries an electrical current which, it turns out is the return path for the electrical display we know as lightning. Much of it has focused on lightning and its effects. Thursday morning's session, co-chaired by Ruhnke, however, dealt with fair weather electricity.
Atmospheric electricity is like a massive photographic flash.
An electrical charge is built up, a switch is closed, and electrons barge across a gas, ionizing it and producing light. But a flash is a complete circuit. In the case of the Earth, Ruhnke explained, the atmosphere completes the circuit. Ultimately, the current returns to Earth through the clear atmosphere. Because it's diffused over most of the globe, it's also quite weak at any given point.