A surprisingly strong geomagnetic storm swept over Earth’s magnetosphere on Sunday, sparking a beautiful green and purple aurora that was visible as far south as the Northeast.

On Friday, the Space Weather Prediction Center was calling for a G1-minor geomagnetic storm. But the solar wind came in hot and fast, and G3-strong storming was observed Sunday evening. The driver of the disturbance was a fast, magnetized solar wind flowing from a coronal hole.

Typically, the strongest geomagnetic storms and the associated aurora are caused by eruptions from the surface of the sun called coronal mass ejections. But the sun is now in the waning part of solar cycle 24, which means solar eruptions are becoming much less common, and storming from coronal holes more so.

Coronal holes are long-lived voids in the solar corona that can persist for weeks to months. They rotate in step with the bright photosphere – the sun as we see it. Over the past few days, a potent coronal hole has rotated toward Earth like a fire hose of unimpeded solar wind.

On Earth, we look for brighter auroras as one of the consequences of strong magnetic storms. The moon was helpful last night, being small and dim in the sky. NOAA forecasters are expecting the storm to linger into Tuesday night, providing another opportunity for aurora viewing in the high-latitudes.