March 18, 2019: Cracks in Earth’s magnetic field? It only sounds like science fiction. In fact, a magnetic crack opened for more than 5 hours on March 16-17. The resulting G1-class geomagnetic storm sparked stunning auroras around the Arctic Circle. “The display I witnessed knocked me off my feet!” says photographer of Göran Strand of Björkliden Sweden:
“What a fantastic show,” he says. “Here is a link to some realtime footage.”
The storm was not predicted, yet it comes as no surprise. The vernal equinox is only days away, and at this time of year cracks often form in Earth’s magnetic field. Solar wind can pour through the gaps to fuel bright displays of Arctic lights.
This is called the the “Russell-McPherron effect,” named after the researchers who first explained it. The cracks are opened by the solar wind itself. South-pointing magnetic fields inside the solar wind oppose Earth’s north-pointing magnetic field. The two, N vs. S, partially cancel one another, weakening our planet’s magnetic defenses.
This cancellation can happen at any time of year, but it happens with greatest effect around the equinoxes. Indeed, a 75-year study shows that March is the most geomagnetically active month of the year, followed closely by September-October–a direct result of “equinox cracks.”