For us to see such a fine display here means something must have happened on a large scale. The location of that something was the surface of the sun. Auroras happen when a large disturbance on the sun's surface sends streams of charged particles into space. These disturbances are called solar flares and coronal mass ejections, or CMEs. They happen frequently around sunspots, and the larger the sunspot, the more likely it is to produce flare and CME activity.
Large sunspots are complex, magnetically driven, cooler areas on the surface of the sun.
Solar activity goes through an 11-year cycle, when sunspots become more numerous during the year or so around the peak of a sunspot cycle. We're now just past the peak of solar activity for the current solar activity cycle. The sunspot associated with the event that produced the March 31 aurora was the biggest one of the current solar cycle. It was so big that it could be seen with the unaided eye if you viewed the sun through a safe solar filter. When these charged particles spewed out by the sun approach Earth after a trip of a day or two, they are drawn toward the Earth's poles like iron filings are attracted to the poles of a bar magnet.