What is that
unusual red halo surrounding this aurora? It is a Stable Auroral Red (SAR) arc. SAR arcs are rare and have only been acknowledged and studied
since 1954. The featured wide-angle
photograph, capturing
nearly an entire SAR arc surrounding more common green and red aurora,
was taken earlier this month from Poolburn, New Zealand, during an especially energetic geomagnetic storm. Why SAR arcs form remains a topic of research, but is likely related to Earth’s protective
magnetic field, a field
created by molten iron flowing deep inside the Earth. This magnetic field usually redirects incoming
charged particles from the Sun’s wind toward the Earth’s poles. However, it also traps
a ring of ions closer to the equator, where they can gain
energy from the magnetosphere during high solar activity. The energetic electrons in this ion ring can collide with and excite oxygen higher
in Earth’s ionosphere than typical auroras, causing the oxygen to glow red. Ongoing research has uncovered evidence that a red SAR arc can even transform into a purple and green STEVE.
Image & info via APOD
Image Credit & Copyright: Tristian McDonald; Text: Tiffany Lewis (Michigan Tech U.)
Source: A SAR
Arc from New Zealand – Scents of Science (myfusimotors.com)
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