Sun activity: Aurora alert for December 23, after M-class flares

UPDATE DECEMBER 23, 2021, AT 16:45 UTC (8:00 AM EDT): NOAA/SWPC has refined its analysis of the CME from December 20th. Their new prediction is that the cloud of solar plasma and magnetic field will reach Earth late on December 23rd or early on the 24th. Their analysis indicates that most of the particles will pass south of Earth but they still are calling for a G1 geomagnetic storm. This should happen on December 24th. This will probably produce aurora for those at higher latitudes however people in regions like the northern US may see aurora on the horizon. Clear skies all you aurora watchers!

SWPC/NOAA issued a G1 level geomagnetic storm watch for December 24. The watch is due to the CME released from the sun with the M-class solar flare on December 20, 2021.
Rotating blue sphere with lighter spots in the middle. In in lower part of the sphere, there is a line created by all the spots, they are very close from each other.
Aurora alert! Here’s an image from December 20, 2021, of an M-class solar flare. The Solar Dynamics Observatory (SDO) produced this image in extreme ultraviolet light. The flare appears as a bright flash in the lower middle of the sun. Image via NASA/SDO.

Aurora alert!

There’s been a small uptick in solar activity over the past two days (December 20 and 21, 2021). The increase comes from the fact that nine sunspot groups (active regions or AR) now pepper the visible face of the sun. Most solar flares – that is, storms on the sun – come from such regions. They often release streams of charged particles into space, called coronal mass ejections (CMEs). The CMEs take several days to travel across space to the Earth. When the solar charged particles in a CME strike Earth, they often cause beautiful displays of the aurora borealis and aurora australis (the northern and southern lights). These events also have the potential to affect power grids and satellites in Earth’s orbit.

At this time, effects from the December 20, 2021, solar storm are expected to arrive at Earth around December 23.

Bright yellow circle with small dark dots (active regions), each labeled from AR12905 to AR12913.
The Solar Dynamics Observatory’s Helioseismic and Magnetic Imager provides visible-light images showing sunspots or active regions (ARs) on the solar disk. Nine sunspot regions were visible on December 21, 2021. Image via

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Black and white view of the sun with dots strung across near the middle.
View at EarthSky Community Photos. | Filipp Romanov in Yuzhno, Morskoy, Russia, took this image of the sun. Filipp wrote: “Sun with large number of sunspots on December 21, 2021 (04:30 UTC), on the winter solstice. Stacked 100 frames from video taken by mobile phone camera through eyepiece of 60mm refractor with solar filter.” Thank you, Filipp!

Multiple M-class solar flares

Three M-class solar flares occurred with their peak X-ray intensities at 11:36 UTC on December 20, 7:50 UTC on December 21, and 11:44 UTC on December 21. The flare on December 20 came from AR12908. The other two M-flares came from a region that hasn’t yet rotated into view on the east limb of the sun. Note that because the sun rises in the east for us, scientists label the limb of the sun that rotates into view, the left side, as east. All three flares produced radio blackouts for tens of minutes. Between these moderate-sized flares, lots of smaller C-class flares have been popping off.

Chart that shows three very vertically zigzag lines in purple, blue and orange with peaks that reach the M scale.
The NASA/GOES satellite uses X-ray emission from the sun to monitor solar flares. This image shows solar X-rays from over the last 3 days (December 19, 20 and 21, 2021). The peaks of the 3 M-flares are circled in red. The axis on the right shows the flare classification from smallest, A, to largest, X. Image via NOAA/SWPC.

Earth-directed CME triggered aurora alert

The flare on December 20 had a small-to-moderate CME associated with it. The forecast from NOAA’s Space Weather Prediction Center (SWPC) is for this CME to reach Earth around 21 UTC on December 23. NASA’s Moon to Mars Space Weather Office produced a model with a similar arrival time though slightly earlier of 16:28 UTC. This group has timing errors of roughly plus or minus 7 hours.

Chart with the sun in the middle, and Earth, Mars, Mercury and Venus around, among others. A green shape moves from 8pm to 4am.
NASA ENLIL model for the December 20, 2021, CME. Image via NASA.

Possible auroras on December 23

The prediction from SWPC is for the CME to give a glancing blow to Earth’s magnetic shield, aka our planet’s magnetosphere, possibly producing increased geomagnetic activity with a G-1 level storm.

This storm in Earth’s magnetosphere could create decent auroral activity on December 23, visible at the higher latitudes. Will the auroral activity extend down into the continential U.S.? We can’t answer that question at this time. Forecasts will be updated as we get closer to the CME’s expected arrival.

Bottom line: A solar storm has caused a stream of charged particles to be headed toward Earth. Aurora alert! Possible northern and southern lights on December 23, 2021.

December 21, 2021

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