Earth's Global Electric Circuit
It’s difficult to comprehend the world before electricity was put to use to power our homes, streets, and cities over 100 years ago. The truth is that electricity has always been with us; it was just unharnessed for human design before the late 1800s. It courses through the atmosphere just as surely as electrical synapses connect thought to feelings and pain to a hot stove in our own bodies' nervous systems. In the atmosphere, electrical currents are collectively called the Global Electric Circuit. In fact, a flash of lightning is not an isolated event within a thunderstorm. It is part of this system that extends throughout Earth’s atmosphere, creating a potential drop of 200,000 to 500,000 volts (200 to 500 kV) between the ground and the ionosphere. Thunderstorms alone send 1 amp (A) of current skyward. But the circuit courses through the atmosphere even on fair-weather days when a slight current of 2 picoamps (or 0.0000000000002 A) flows from every square meter of ground upward.
Scientists have long been interested in understanding various parts of the Global Electric Circuit, but the system is vast and variable over time and space. Understanding it in its entirety has just begun. But that doesn’t mean that scientists haven’t been studying its various components and trying to make sense of them.
From 1909 to 1929, Carnegie, a yacht that was nearly entirely non-magnetic and wood-hulled, sailed scientists around the world – nearly three-hundred thousand miles through its oceans – carefully locating and measuring then unknown magnetic influences in the atmosphere. The Carnegie's many voyages were part of the Carnegie Institution’s program that included an ambitious magnetic, electric, and oceanographic survey coupled with magnetic and electric surveys of land areas in many parts of the world. Eventually it carefully located and measured unknown magnetic influences in the atmosphere, and gave scientists something still used today called the Carnegie Curve, the characteristic universal variation of the atmospheric electric field.
Scientists today at the National Center for Atmospheric Research, the University of Colorado, Pennsylvania State University, and elsewhere around the world are working to better understand the Global Electric Circuit from its smallest scale to its largest, and across large variances in time. As their understanding grows, their goal to build a scientific model of the system will advance, which in turn will allow still greater experimentation and advances in understanding this complex system and its connection to other natural systems. Learn more about it from Professor Jeffrey Forbes audio interview, Exploring How the Lower Atmosphere Influences Space Weather, and additional content for download.
It's difficult to believe that over 250 years ago, Benjamin Franklin suspected, but wasn't sure, that lightning and electricity were one and the same. We've definitely come a long way, but when it comes to electricity in the atmosphere, it's also true that we still have much to learn and discover.
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