This lightning strike over Boulder, Colo., is one of the 100 strikes per second that occur around the globe. This continuous generation of current sustains the global electric circuit—a mass of electrical currents constantly circulating throughout the atmosphere—which scientists are working to incorporate into climate models. Credit: John Jorgensen
Source: Journal of Geophysical Research: Atmospheres

Electricity courses through the atmosphere around us, bouncing between the Earth’s surface and the positively charged ionosphere 100 kilometers above. This massive collection of electrical currents is known as the global electric circuit (GEC). Thunderstorms have long been considered generators of the GEC; in fact, electrified clouds in the atmosphere help to maintain a potential difference between the ground and the ionosphere of about 250 kilovolts, or about 28,000 9-volt batteries.

Global climate models today take most atmospheric processes into account, but the global electric circuit is often overlooked. For example, conductivity generally increases from the Earth’s surface up toward the ionosphere, but clouds and aerosols can perturb the conductivity and alter the circuit. Present-day climate models can resolve only convective systems that stretch on for hundreds of kilometers, whereas individual clouds and storms are usually too small for present climate models to pick up on.

Representation of electrical processes occurring within the global electric circuit. The conductivity within the atmosphere is affected by ion production and loss mechanisms, whereas the global distribution of electrified clouds maintains a potential difference between the ground and ionosphere. Credit: Allison Dean and Greg Lucas

To fill in the gap, Lucas et al. created a three-dimensional model of the electric fields and currents circulating through the atmosphere that can be incorporated into the Community Earth System Model (CESM1). Here the researchers present a new method they used to elucidate the parameters of atmospheric conductivity for climate models by assessing the effects of cosmic rays, radon emission at the Earth’s surface, solar activity, and clouds and aerosols on the GEC.

The team ran the model for 30 days and then validated the simulated electric fields by comparing them to observations from two field stations in Vostok and Concordia, Antarctic—the only polar research stations where long-term data sets were available.

The study found that, globally, variations in the magnetosphere—a region surrounding the Earth where the planet’s magnetic field interacts with the solar wind—have little effect, as positive and negative potentials cancel each other out. But locally, the effect of the magnetosphere on atmospheric electric currents can be drastic. The analysis also revealed that the model and observations were reasonably well matched in terms of the magnetospheric processes. However, the electrical peaks were slightly larger in the observed data, suggesting that some fine-tuning is yet required. Still, the new model should provide scientists with ample opportunities to further characterize the GEC and the processes that act on it and perhaps elucidate how atmospheric electricity affects climate. (Journal of Geophysical Research: Atmospheres, doi:10.1002/2015JD023562, 2015).

—Kate Wheeling, Freelance Writer

Citation: Wheeling, K. (2016), Considering atmospheric electricity in climate models, Eos, 97, doi:10.1029/2016EO049811. Published on 7 April 2016.

Text © 2016. The authors. CC BY-NC-ND 3.0
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