When solar storms strike Earth, the blast of charged particles causes disturbances in our planet’s magnetic field both in space and on the ground. High above Earth, the oncoming shock waves of particles streaming off of the Sun—called solar wind—distort the planet’s magnetic field lines as they wrap around its nightside, as seen in the video below.
This can create spectacular auroras around the poles. Meanwhile, on the ground, the Earth’s magnetic field often experiences a spike in intensity in the direction parallel to the ground.
Now Sun et al. have published numerical simulations that show that these responses are actually part of one long chain reaction from space to the ground, linked by electrical currents in Earth’s magnetosphere and ionosphere.
In the team’s simulations, the shock first encounters the dayside of Earth’s magnetic field, where the field lines are compressed by the onslaught of the solar wind. But as the shock wave washes over the planet, wrapping around to the nightside, a funny thing happens: Instead of the field lines being compressed everywhere, some of the field lines fall away at the flanks, creating two areas of low magnetic pressure hundreds of kilometers above the dawnside and duskside of the planet. And just as low-pressure weather systems in Earth’s atmosphere generate cyclones or tornadoes, these areas of low magnetic pressure can trigger swirling “tornadoes” of electrical current.
Like an electric motor, this vortex drives currents coursing down the magnetic field lines toward the ground, deep into the Earth’s ionosphere, which can cause the magnetic field on the ground to jump sideways in intensity.
Previous studies mainly considered the impacts of solar storms in space separately from the effects on the ground, although scientists have widely suspected that these events were connected. This is the first study to show in numerical detail just how the magnetic field responses in both regions are linked, building what the authors call a bridge between the impacts of solar storms in space and on the ground. (Journal of Geophysical Research: Space Physics, doi:10.1002/2014JA020754, 2015)
—Mark Zastrow, Freelance Writer
Citation: Zastrow, M. (2015), Electric “tornadoes” in space drive disturbances down to Earth, Eos, 96, doi:10.1029/2015EO041529. Published on 23 December 2015.