Via Spaceweather.com
Todd Salat is a veteran photographer of auroras in Alaska. Over the years he has chased the light and seen most of what nature has to offer. But on November 22, when these weird-shaped auroras appeared overhead, even he was confused:
“Last Friday around 4 o'clock in the morning, I saw these strange auroras drifting over south-central Alaska,” Zarate said. “It came from the northwest and I was like, wow! It looks like the letter E to me.
Zarate may have witnessed a “black aurora”. They are dark rings or black spots that sometimes appear in ordinary auroras. For example, take a look at Figure 1 from the research paper on this topic. Some researchers call them “anti-auroras.” The black aurora in Salat's photo is circled here.
Ordinary auroras are caused by electrons falling from space. Black Aurora is the opposite. Instead of falling like raindrops, the electrons are pushed upwards back into space. On January 14, 2001, Europe's Cluster spacecraft fleet flew over the black aurora and witnessed the entire process:
Sensors on the spacecraft detected strong positive electric fields in the black aurora region. These fields reverse the normal downward rain of electrons that cause aurorae.
Research into black auroras is still in its infancy, and forecasters can't yet predict when and where they might appear. Aurora watchers, be on the lookout for black the next time a geomagnetic storm breaks out. Aurora Alert: SMS text.
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