Rare sights
STEVE, red SAR arcs, pulsating aurora and the southern lights.
STEVE
STEVE (Strong Thermal Emission Velocity Enhancement) is a narrow, mauve or whitish ribbon running east to west across the sky, sometimes with green vertical stripes beside it known as the "picket fence". It was named by aurora watchers in Canada and then studied by scientists. It isn't aurora in the usual sense: it's lit by a very fast, hot stream of charged gas flowing through the upper atmosphere, closer to the equator than the auroral oval. It usually appears after a substorm, lasts under an hour and is seen most often around the equinoxes.
SAR arcs
A stable auroral red (SAR) arc is a faint, uniform band of red light, often seen during and after strong storms, closer to the equator than the main aurora. It's caused by heat leaking down from the magnetosphere into the upper atmosphere, rather than by particles crashing in, so it's purely red and barely moves. It's often too faint for the eye but clear on camera. SAR arcs have been seen turning into STEVE.
Pulsating aurora
After a substorm, and especially in the early morning hours, the aurora can break up into patches that switch on and off every few seconds, like a slow heartbeat. They're driven by waves high in the magnetosphere, called chorus waves, that knock electrons down into the atmosphere in bursts. Pulsating aurora is common but faint, so it's often missed.
The southern lights
The aurora australis happens at the same time as the northern lights, as a near mirror image around the southern magnetic pole. Most of the southern oval lies over Antarctica and the ocean, so it's seen less often. During strong storms it reaches Tasmania, southern Australia, New Zealand, Patagonia and the Falkland Islands. Polar Lights forecasts it for places in the southern hemisphere: see Does Polar Lights work in the southern hemisphere?