© Matti Helin
You've heard of auroras--green and purple lights that dance in the sky during geomagnetic storms. But have you ever heard of an
SAR? Stable Auroral Red arcs (SARs) were discovered in 1956 at the beginning of the Space Age and have been recorded by
cameras on satellites hundreds of times since.
Most aurora watchers have never seen one, though, because they are usually invisible to the human eye. Last night in southern Finland, Matti Helin saw one.
"The SAR was visible to the naked eye for nearly 30 minutes and, after fading a bit, remained visible to my camera for another hour and a half," says Helin. "Normally we see auroras in the north, but this stable red arc appeared to our south. It was strange shooting in that direction :D"
SARs are
related to auroras, but they are not the same. Regular auroras appear when high-energy particles rain down along polar magnetic field lines, hitting the atmosphere (100-200 km high) and causing it to glow like the picture tube of an old color TV. SARs form differently.
They are a sign of heat energy leaking into the upper atmosphere (~400 km high) from Earth's
ring current system.
Normally, SARs become visible to the naked eye only during strong geomagnetic storms. Last night's G1-storm was far from strong, but the arc appeared anyway--further proof that auroras can be full of surprises.
Comment: This is the 2nd major flooding event for the island nation within the last 3 weeks and the 5th in the past 17 months, for details see: National disaster declared in Trinidad after catastrophic flooding
Flash floods ravage parts of Trinidad and Tobago
Parts of Trinidad swamped by flood waters after 24 hours of non-stop rainfall
Floodwater as high as 8 feet in Williamsville, Trinidad