Series of CMEs impact Earth, sparking G3 – Strong geomagnetic storming


A coronal mass ejection (CME) produced by the long-duration M1.7 solar flare1 at 03:01 UTC on November 2, 2021, reached Earth at 19:57 UTC on November 3, sparking G3 – Strong geomagnetic storming. The CME overtook and merged with at least one, possibly two or more, previously produced CMEs that were on their way toward Earth.

Wind speeds increased to greater than 700 km/s, Bt increased to 20nT, and the Bz component reached a southward deflection of -16 nT as the CMEs hit our planet.

The geomagnetic field ranged from quiet to unsettled levels due to the influence of a positive polarity CH HSS before the impact at 19:57 UTC, with a deviation of 21nT measured at the FRD magnetometer in response to the CME shock arrival.

Geomagnetic K-index of 4 threshold was reached at 21:00 UTC, followed by K-index of 5 (G1 – Minor geomagnetic storm) at 21:24 UTC, and K-index of 6 (G2 – Moderate) at 21:46 UTC.

K-index of 7 (G3 – Strong geomagnetic storm) threshold was reached at 23:59 UTC and again at 08:48 UTC and 09:34 UTC on November 4.

G3 – Strong geomagnetic storm 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 impact produced intense auroras around the Arctic Circle, allowing aurora tour guide Markus Varik to capture the outburst from Tromsø, Norway.

Varik is one of the most experienced guides in Norway, said Tony Phillips of SpaceWeather.com, but Even Markus was impressed.3

"The auroras were strong, one of the best displays in years. I am very tired, but happy."

Image courtesy Markus Varik/SpaceWeatherGallery. Captured on November 3, 2021 @ Tromso, Norway 

A conglomeration of CMEs from Regions 2887 and 2891 are anticipated to continue keeping solar wind parameters enhanced through November 6.2

Unsettled to active levels are expected on November 5 and 6 as CME effects wane.

Solar activity has a slight chance for additional M-class flare activity (R1-R2, Minor-Moderate Radio Blackouts) today. There's also a chance for C-class flares through November 6.


1 Long-duration M1.7 solar flare erupts from geoeffective AR 2981, CME impact expected – The Watchers

2 Forecast Discussion Issued: 2021 Nov 04 0030 UTC Prepared by the U.S. Dept. of Commerce, NOAA, Space Weather Prediction Center

3 CME impact sparks strong geomagnetic storm – SpaceWeather

Featured image credit: Markus Varik via SpaceWeather. Acquired on November 3, 2021 at Tromsø, Norway.


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