AURORAS SIGNAL THE APPROACH OF FALL: Northern autumn is coming. We know this because auroras are appearing for no special reason. “I didn’t expect to see anything last night,” reports Yuichi Takasaka of Yellowknife in the Northwest Territories of Canada . “The forecast called for no geomagnetic storms.” Yet the auroras were there anyway:
“The auroras were very active,” says Takasaka. “We were so very lucky!!!”
What’s going on? As autumn approaches, cracks are opening in Earth’s magnetic field. Solar wind pours in to spark auroras even without big geomagnetic storms. This is called the the “Russell-McPherron effect,” named after the researchers who first explained it. As a result of the cracks, September and October are two of the best months of the year to see auroras.
“The display was remarkably pink,” notes Takasaka. Pink is a sign of nitrogen. Most auroras are green–a verdant glow caused by particles from space hitting oxygen atoms 100 km to 300 km above Earth’s surface. Pink appears when those particles descend lower than usual, striking nitrogen molecules at the 100 km level and below.