The sky glowed green and pink over the Upper Midwest on Tuesday night as the northern lights pushed south. The aurora was the result of a moderate geomagnetic storm, which was caused by a fire hose of solar energy pointed at Earth.
The sun can generate geomagnetic storms in two ways. The first is a coronal mass ejection, or CME, which is probably what people are most familiar with. They emanate from sun spots, which look like little dark splotches on the surface of the sun. These dark spots occasionally explode with energy, and if it happens to be pointed at Earth at the time, it will reach us in just a couple of days and roil up the planet’s magnetosphere.
The other way we can get geomagnetic storms — and thereby beautiful aurora — is a coronal hole. Instead of exploding occasionally, coronal holes are like giant leaks. The stream of “solar wind” from a coronal hole tends not to be as intense as a CME, but it’s more persistent, and it can generate northern lights just the same.
“The brilliant auroras were sparked by the energy carried from the Sun in the solar wind as a high-speed stream,” said Joe Kunches, the Capital Weather Gang’s space weather expert. “Coronal holes are the nozzles from which the fast stream emanates. These structures are most prevalent at this point in the solar activity cycle when sunspots are rare.”
This particular hole is near the “north pole” of the sun, and it “continues to buffet Earth’s magnetosphere causing overall, planetary geomagnetic responses,” said the Space Weather Prediction Center.
Translation: Solar energy is streaming toward Earth this week and vexing our upper atmosphere. It’s a geomagnetic storm, and the visual result of the storm is an aurora.
On a scale of 1 to 5, Tuesday night’s geomagnetic storm was just a 2, but it was more than enough to push the aurora into the Upper Midwest and even New York. The Space Weather Prediction Center expects category-1 storm through Thursday night, which means the aurora would be harder to see in the Lower 48.