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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