Last night’s aurora crept up out of nowhere. Space weather forecasters predicted a very small chance of a minor auroras for mid-latitudes, but a sudden change in the direction of the interplanetary magnetic field (IMF) set Earth’s magnetic field a-jitter, sparking a nice display of northern lights. The storm’s still raging across Siberia this afternoon with no sign of letting up.
The IMF is a part of the sun’s magnetic field carried into interplanetary space by the solar wind, a high-speed outflow of subatomic particles, mostly electrons and protons. Scientists call this soup of charged particles a plasma. Because the sun rotates, solar plasma travels away from the sun in grand spirals much like water spraying from one of those rotating lawn sprinklers.
Embedded within the sun’s plasma swirls are portions of its magnetic field. As the IMF sweeps past Earth, it normally glides by, deflected by our protective magnetic field, and no one’s worse for the wear. But when solar magnetic field points south – what’s called a southward Bz – it can hook up with Earth’s northward-pointing magnetic field. Once linked, the IMF dumps its baggage of high-speed particles into our atmosphere to light up the sky with aurora and set satellite operators on edge.
That’s exactly what happened yesterday evening. The Bz turned sharply south and Earth’s private space was invaded by a particle horde. Coronal mass ejections and constant fluctuations in the solar wind can tip the Bz this way and that and set the scene for northern lights.
Last night’s storm rated a G2 or moderate on NOAA’s space weather scale. G2s not only produce auroras but can cause fading of radio transmissions at high latitudes, drag on satellites and even trigger voltage alarms on power grid stations.
The aurora will likely continue through this evening, so be on the watch. Check the Kp index and if it’s up to “5″ or higher (in the red zone), chances are decent you’ll see aurora at least from the northern U.S. Another cool tool is the Ovation aurora site that displays a beautiful graphic representation of the complete auroral oval. When you see the oval’s edge creep up to or over the northern U.S. auroras are almost certain to show. Of course you’ll need a clear sky, which is often the trickiest thing to find.
I’ll update the blog this evening if and when auroras come back to green-wash the sky.