Earth’s biggest electrical circuit can be found in its atmosphere, where currents flow between the ground and the ionosphere. This global electrical circuit (GEC) gets power from thunderstorms pumping positive charge into the ionosphere—the electrically charged layer of the Earth’s upper atmosphere. This charge gradually returns to the ground during fair weather.
Now Jánský and Pasko have introduced a new model to simulate this process in greater detail while also improving the speed of the simulations with a few mathematical tricks. They use a spherical coordinate system, in which locations are defined using angles from an axis or on a plane—like latitude and longitude. Previous simulations used a coordinate system that treated thunderstorms like cylinders or introduced several constraints on electric potential. Spherical coordinates allow the team to calculate the electric potential in the system directly from first principles, making the new model more precise.
Another innovation involves a technique called impulse response. Consider an acoustical analogy: applying a realistic reverberation effect to make a musical recording sound as if the players were in a spacious concert hall. Instead of calculating the physics of every note bouncing around the auditorium, technicians make a sample recording of a single sound. A crack of a snare drum reverberates through the hall, capturing its characteristic echoes—an impulse response. Audio engineers digitally meld the waveform of that impulse with a recording of an entire musical performance, mathematically applying the reverberation to every note to make an entire orchestra sound as if it’s playing in a concert hall without using much computational power.
The authors apply this concept to modeling thunderstorms and the global electric circuit. By precalculating the overall effect of a single charge introduced in their simulations, they create impulse responses that they use to efficiently calculate the response of the entire system to changes in current and their impact on the GEC.
They report that this model captures the behavior of electrical currents in a thundercloud, including how the movement of charges within the cloud creates an imbalance, and the instantaneous burst of electric potential that a cloud-to-ground lightning bolt injects into the ionosphere. They conclude that such lightning strikes are responsible for about 4% of the total ionospheric potential in the GEC, which is in line with previous studies—a further vote of confidence for their new approach. (Journal of Geophysical Research: Space Physics, doi:10.1002/2014JA020326, 2014)
—Mark Zastrow, Freelance Writer
Citation: Zastrow, M. (2015), Lightning “impulses” improve models of global electrical circuit, Eos, 96, doi:10.1029/2015EO034277. Published on 19 August 2015.