Auroras appear when energetic particles from space rain down on Earth's atmosphere during geomagnetic storms. If STEVE is an aurora, they reasoned, it should form in much the same way. On March 28, 2008, STEVE appeared over eastern Canada just as NOAA's Polar Orbiting Environmental Satellite 17 (POES-17) passed overhead. The satellite, which can measure the rain of charged particles that causes auroras, went directly above the purple ribbon. Gallardo-Lacourt's team looked carefully at the old data and found ... no rain at all.
"Our results verify that this STEVE event is clearly distinct from the aurora borealis since it is characterized by the absence of particle precipitation," say the researchers. "Interestingly, its skyglow could be generated by a new and fundamentally different mechanism in Earth's ionosphere."
Another study has shown that STEVE appears most often in spring and fall. With the next equinox only a month away, new opportunities to study STEVE are just around the corner. Stay tuned and, meanwhile, read the original research here.