Multiple CMEs impact Earth, sparking G3 – Strong geomagnetic storm

Multiple coronal mass ejections (CMEs) produced on November 27 and 28, 2023, impacted Earth on November 30 and December 1, sparking G3 – Strong geomagnetic storm. Similarly to the last G3 storm, on November 5, spectacular aurora sightings were reported from both hemispheres.

The solar wind parameters observed during the 24-hour period ending at 00:30 UTC on December 2, 2023, signaled the arrival of multiple CMEs, initially detected on November 27 and 28.

The first notable CME impact, which occurred at 23:37 UTC on November 30, led to an increase in solar wind velocity from about 335 km/s (208 mph) to approximately 440 km/s (273 mph). Concurrently, the total magnetic field strength showed a significant rise from 5 nT to 12 nT.

A second CME, produced by M9.8 solar flare on November 28, was observed at 08:53 UTC on December 1, causing further escalations in solar wind speeds from approximately 406 km/s (252 mph) to near 510 km/s (317 mph).

During this event, the total magnetic field also experienced an increase, moving from 15 nT to 25 nT. Throughout the remainder of the observation period, the total field fluctuated between 13 nT and 28 nT, while solar wind speeds varied from around 480 km/s (298 mph) to 560 km/s (348 mph). The Bz component of the magnetic field ranged around +/-26 nT, with a variable Phi angle.

Similarly to the last G3 – Strong geomagnetic storm, on November 5, spectacular aurora sightings were reported from both hemispheres.

Forecasts indicate that the influence of these CMEs is expected to persist through midday on December 2, followed by a gradual recovery towards nominal conditions through December 3. Early on December 4, a negative polarity coronal hole high-speed stream (CH HSS) is anticipated to become geoeffective, potentially increasing solar wind speeds to the range of 600 – 700 km/s (373 – 435 mph), based on historical recurrence patterns.

In terms of geospace impact, the geomagnetic field was observed at active to G3 – Strong storm levels due to the CME arrivals from November 27 and 28.

The forecast suggests that the geomagnetic field will experience unsettled to G2 – Moderate storm levels, with a possibility of G3 – Strong storming on December 2 as the effects of the CMEs continue. A return to quiet to unsettled levels is expected on December 3 as the activity slowly wanes.

Unsettled to G2 – Moderate storm levels are likely again on December 4 as a negative polarity CH HSS is expected to become geoeffective.

References:

¹ Forecast Discussion – Issued 2023 Dec 02 0030 UTC -Prepared by the U.S. Dept. of Commerce, NOAA, Space Weather Prediction Center

Featured image credit: Katarina Srsenova via SpaceWeather. Captured on December 1, 2023 from Iceland.