APOD: 2024 January 3 Б A SAR Arc from New Zealand
Explanation:
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.
Authors & editors:
Robert Nemiroff
(MTU) &
Jerry Bonnell
(USRA)
NASA Web Site Statements, Warnings,
and Disclaimers
NASA Official: Jay Norris.
Specific
rights apply.
A service of:
LHEA at
NASA /
GSFC
& Michigan Tech. U.
