Friday, February 9, 2024

Strongest X-Flare of Cycle 25 Erupted Today

It wasn't pointed at Earth, so all effects observed so far and all predicted are pretty mild, but sunspot group AR3575 burped out an X3.4 class solar flare and Coronal Mass Ejection (CME) this morning at 1314 UTC or 8:14 AM EST.  Group AR3575 had rotated around the sun's limb in the last 48 hours so it was pointed at over 90 degrees away from Earth.  NASA's Solar Dynamics Observatory (SDO) recorded the extreme ultraviolet flash:

While instruments in space don't all have this handicap, the instruments that measured the flare's strength could have had their readings reduced by its position over the limb of the sun so it's the realm of possibility that this flare was stronger than X3.4.  The previous strongest flare of cycle 25 was an X2.8 flare on Thursday, Dec. 14.  

This morning's flare triggered a warning of an S2 or Moderate Solar Radiation Storm.  NOAA lists these characteristics of an S2 storm. 

Biological: Passengers and crew in high-flying aircraft at high latitudes may be exposed to elevated radiation risk.
Satellite operations: Infrequent single-event upsets possible.
Other systems: Small effects on HF propagation through the polar regions and navigation at polar cap locations possibly affected. has a video that shows the eruption in several parts of the spectrum, viewable here.  

As we move toward or through the peak of cycle 25, this sort of thing is more likely than a year ago.  This is the sun today as posted on, and there's an obvious, big sunspot group in the southern hemisphere (3576) that has the magnetic configuration to produce more flares and CMEs. 

For my fellow hams, solar terrestrial indices have been good, with solar flux in the 180s and K index has remained low until the last 3 hour window of the 9th, when it popped up to K=3.  I've heard nothing even remotely like the conditions that brought in New Zealand and Australia on 6m (50 MHz) a couple of weeks ago.


  1. It's really dead here tonight, too. The only activity I could find was on 75M.

    1. 30m was pretty active here in the 0230-0330Z range.

      NOAA is still reporting we're having an S2-class Solar Radiation Storm, but reality seems to be rather "meh."