CME impact sparks unexpected G3 – Strong geomagnetic storm, red aurora in Missouri, U.S.

Solar wind conditions became enhanced beginning at 04:13 UTC on April 19, 2024, due to coronal mass ejection (CME) impact, resulting in unexpected G3 – Strong geomagnetic storming just before 20:00 UTC.

Following the CME arrival, total field strength reached 18 nT and the Bz component was sustained southward after 04:10 UTC with a peak of -17 nT observed, according to the SWPC.

Geomagnetic K-index of 4 threshold was reached at 07:50 UTC, followed by K-index of 5 (G1 – Minor geomagnetic storm) at 14:15 UTC. Geomagnetic K-index of 6 threshold (G2 – Moderate geomagnetic storm) was reached at 19:40 UTC, followed by K-index of 7 (G3 – Strong geomagnetic storm) threshold at 19:52 UTC.

Under G3 – Strong geomagnetic storm conditions (impact is primarily poleward of 50 degrees Geomagnetic Latitude), power system voltage irregularities are possible, and 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. Intermittent satellite navigation (GPS) problems are likely, including loss-of-lock and increased range error. HF (high frequency) radio may be intermittent and aurora may be seen as low as Pennsylvania to Iowa to Oregon.

While the strong storm was brief, it managed to produce impactful auroras, including red auroras as far south as Iowa and Missouri. Northern lights were also sighted across Europe, with reports coming in from Bled, Slovenia, and even Corsica in the Mediterranean Sea. Additionally, red aurora was also seen and captured from Tasmania.

Solar activity reached moderate levels in 24 hours to 00:30 UTC on April 20. Region 3647 produced two M-class flares, the largest of which was an M2.1 flare at 04:53 UTC on April 19. The second was M1.0 at 13:06 UTC.

Other notable activity included a large prominence eruption on the SE limb, beginning at around 04:00 UTC on April 19. The associated CME is not Earth-directed.

Solar activity is expected to remain at moderate levels through April 21, with M-class flares expected (75%) and a slight chance for X-class flares (20%), due to the flare potential of several active regions on the visible disk.

Periods of unsettled to active levels are expected on April 20 and 21 due to continued CME activity, coupled with the onset of negative polarity coronal hole high speed stream (CH HSS) influences and the anticipated arrival of multiple CMEs from April 16 to 18.

Quiet to unsettled conditions are expected on April 22 due to negative polarity CH HSS influence.

References:

¹ Forecast Discussion – Issued: 2024 Apr 20 0030 UTC – Prepared by the U.S. Dept. of Commerce, NOAA, Space Weather Prediction Center

Featured image credit: MissouriSkies (stillshot)