CME impacts Earth, sparking G3 – Strong geomagnetic storm


A coronal mass ejection (CME) produced by a filament eruption around 10:00 UTC on May 9, 2021, has reached Earth at 06:43 UTC on May 12. G3 – Moderate geomagnetic storm levels were observed at 12:59 UTC.

The CME arrived at the DSCOVR spacecraft at 05:47 UTC. Solar wind speed increased from an average of 320 km/s to 430 km/s at 05:48 UTC and to 450 km/s at 07:41 UTC

Similar jumps were observed in density, temperature, and magnetic field.

After a short period of southward Bz (-7nT) immediately after shock arrival, Bz was predominantly positive.

The Bt reached 20 nT but had declined to around 10 nT by 12:30 UTC.  Bz also reached 20nT, but it was stubbornly positive during that roughly two-hour period.

Earth's magnetic field was quiet until 06:43 UTC when the CME arrived. The arrival was marked by a 51 nT sudden impulse at the Fredericksburg, VA ground magnetometer, SWPC said.

Geomagnetic K-index of 5 (G1 – Minor geomagnetic storm) threshold was reached at 12:30 UTC, followed by K-index of 6 (G2 – Moderate) at 12:32 UTC and K-index of 7 at 12:58 UTC.

ALERT: Geomagnetic K-index of 7
Threshold Reached: 2021 May 12 1258 UTC
Synoptic Period: 1200-1500 UTC

Active Warning: Yes
NOAA Scale: G3 – Strong

NOAA Space Weather Scale descriptions can be found at

Potential Impacts: Area of impact 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.

The CME was produced by a filament eruption at 10:00 UTC on May 9.

Featured image credit: SWPC

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One Comment

  1. If a mild CME could produce this geomagnetic storm, then what will happen during peak solar maximum?……..I have stated many, many times over the last a few years, that the next solar maximum will produce the highest energetic events ever recorded and that will have devastating consequences on the physical structures of our planet. The reason why the next solar maximum will produce colossal solar flares and coronal mass ejections is because the Sun will be in its highest position above the galactic plane.

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