"As noted scientist Richard Feynman once explained, "the earth is negative, and the potential in the air is positive." That tension is maintained by thunderstorms, which are happening at some point in the world at any given time. But that tension varies throughout the planet. On a day without a cloud in the sky, APG levels can get up to 100 volts per meter, the metric used to measure the strength of an electric field. However, in a thunderstorm those levels can rise up to 10 kilovolts per meter, exponentially larger."