Zonnevlammen, Zonnestormen en CME #4:

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Unexpected G4 – Severe geomagnetic storm

A combination of factors led to unexpectedly strong geomagnetic storm levels on Thursday, March 23, and Friday, March 24, 2023. The storm reached G3 – Strong levels at 14:49 UTC on March 23 and escalated to G4 – Severe at 04:04 UTC on March 24. The precise cause of this geomagnetic storm is still under investigation, but it is possible that coronal mass ejections (CMEs) from March 20 to 21 played a role.

This is the most intense geomagnetic storm in nearly 6 years.

Geomagnetic storms of this intensity occur on average 100 times per solar cycle

Initially, SWPC predicted that the arrival of a co-rotating interaction region (CIR) ahead of a recurrent, negative polarity coronal hole high-speed stream (CH HSS) would disturb the geomagnetic field, leading to G1 – Minor conditions on March 23. This disturbance, along with nearby transients, was expected to produce G2 – Moderate conditions on March 24. However, contrary to predictions, the geomagnetic field exhibited G3 – Strong levels on March 23 and G4 – Severe early on March 24.

The unanticipated intensity of the geomagnetic storm may have resulted from a stealthy CME or a combination of events, including CMEs from March 20 and 21.

G3 – Strong geomagnetic storm potential impacts:

The area of impact is primarily poleward of 50 degrees Geomagnetic Latitude.

Induced Currents – Power system voltage irregularities possible, false alarms may be triggered on some protection devices.
Spacecraft – Systems may experience surface charging; increased drag on low Earth-orbit satellites and orientation problems may occur.
Navigation – Intermittent satellite navigation (GPS) problems, including loss-of-lock and increased range error may occur.
Radio – HF (high frequency) radio may be intermittent.
Aurora – Aurora may be seen as low as Pennsylvania to Iowa to Oregon.
G4 – Severe geomagnetic storm impacts:

The area of impact is primarily poleward of 45 degrees Geomagnetic Latitude.

Induced Currents – Possible widespread voltage control problems and some protective systems may mistakenly trip out key assets from the power grid. Induced pipeline currents intensify.
Spacecraft – Systems may experience surface charging; increased drag on low earth orbit satellites, and tracking and orientation problems may occur.
Navigation – Satellite navigation (GPS) degraded or inoperable for hours.
Radio – HF (high frequency) radio propagation sporadic or blacked out.
Aurora – Aurora may be seen as low as Alabama and northern California.

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Strongest solar storm in nearly 6 years slams into Earth catching forecasters by surprise

The most powerful solar storm in nearly six years slammed Earth today (March 24), but strangely, space weather forecasters didn't see it coming.

The geomagnetic storm peaked as a severe G4 on the 5-grade scale used by the U.S. National Oceanic and Atmospheric Administration (NOAA) to assess the severity of space weather events. The storm's unexpected ferocity not only made auroras visible as far south as New Mexico in the U.S., but it also forced spaceflight company Rocket Lab to delay a launch by 90 minutes.

Geomagnetic storms are disturbances to Earth's magnetic field caused by solar material from coronal mass ejections (CME) — large expulsions of plasma and magnetic field from the sun's atmosphere. It turns out that this particular geomagnetic storm was triggered by a "stealth" CME which — as the name suggests — is rather tricky to detect.

NOAA's National Space Weather Service originally announced a "geomagnetic storm watch" on March 22(opens in new tab), to come into effect on 23-25 March with possible moderate G2 storm conditions expected on March 24. So forecasters weren't completely caught off-guard, they however didn't expect a magnitude G4 storm.

It wasn't until 00:41 a.m. EDT ( 0441 GMT) on March 24 that NOAA uprated the warning to a severe G4 storm, which was after a stronger than forecasted G3 storm (opens in new tab)escalated to a G4 at 12:04 a.m. EDT (0404 GMT).

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Impulsive X1.2 solar flare erupts
An impulsive solar flare measuring X1.2 at its peak erupted from AR 3256 at 02:33 UTC on March 29, 2023. The event started at 02:18 and ended at 02:40 UTC.

There were no radio signatures suggesting a coronal mass ejection (CME) was produced. Even if it was, the location of this region does not favor Earth-directed CMEs.

Radio frequencies were forecast to be most degraded over the West Pacific Ocean, parts of eastern China and Russia, Vietnam, Laos, Thailand, Cambodia, Japan, Philippines, Indonesia, Papua New Guinea and Australia.

Region 3256 is now approaching the west limb and will start its farside rotation in a couple of days.

Solar activity was at low levels until this solar flare and is expected to be at low levels, with a slight chance for M-class flares through March 31.

The greater than 10 MeV proton flux was at background levels and the greater than 2 MeV electron flux reached high levels with a peak flux of 1 810 pfu observed at GOES-16 at 14:20 UTC on March 28.1

The greater than 10 MeV proton flux is expected to continue at background levels through March 31. The greater than 2 MeV electron flux is expected to reach high levels through March 31, possibly decreasing to moderate levels on March 30 with the arrival of the next negative polarity CH HSS.

Solar wind parameters were mostly at background levels in 24 hours to 00:30 UTC on March 29. The IMF was relaxed with total field averaging around 6 nT and Bz undergoing few if any significant southward deviations. Wind speeds were unreliable from DSCOVR given the low density environment, but ACE showed speeds generally at 400 km/s or less. The phi angle was oriented in a negative solar sector towards the Sun. Nominal levels are expected to continue through March 29 and the first half of March 30. Another negative polarity CH HSS is forecast to arrive midday on March 30, with elevated levels of activity lasting through March 31.

The geomagnetic field was at quiet levels on March 29. Mostly quiet levels are expected on March 29 and the first half of March 30.

Active conditions are expected starting midday on March 30 through March 31 with the onset of a negative polarity CH HSS. There is also a chance for G1 – Minor geomagnetic storms on March 30 and 31 with this activity.