07 Nov A Stormy weekend: CME’s collide with Earth

The past two days (5–6 November 2023) have seen a ramp-up of the Sun’s activity. Earth experienced a slew of geomagnetic storms over the weekend, ranging from G1/Minor (Kp 5) to G3/Strong (Kp 7). The storms were a result of three coronal mass ejections (CMEs) that left the Sun a few days before. The first CME came from a filament eruption on the southeast part of the Sun late on 31 October, the second CME came from a filament eruption off the northeast part of the Sun early on 2 November, and the last CME was from an enormous filament eruption that came off the northwest quadrant of the Sun on 3 November.

When these CMEs bombarded the Earth’s magnetic field late on 4 November and early on 5 November, they resulted in a disturbance storm time (Dst) as low as -160 nT, which then resulted in the geomagnetic storms. Geomagnetic storms can cause systems such as the Global Navigation Satellite System (GNSS) and high-frequency (HF) communication to be affected.

However, there is an upside to these storm events: high-latitude regions get to observe beautiful, bright lights in the sky called auroras. These hues of bright lights (usually green, blue, or red) happen when the energetic particles from the solar wind and the CMEs enter the Earth’s upper atmosphere by travelling via the Earth’s magnetic field lines that enter the poles. When these energetic particles enter the upper atmosphere, they collide with the particles within the atmosphere and cause their excitation (rise to a higher energy state). When the particles get de-excited (return to their low-energy state), they release photons of a particular wavelength, which we see as the marvellous light in the sky. Unfortunately, it is highly unlikely to witness these lights in South Africa since we are in a mid-latitude region and auroras occur at high latitudes.

Coronagraph imagery showing the CME that came from the filament eruption observed on 2 November from the northeast quadrant of the Sun.

Coronagraph imagery showing the CME that came from the filament eruption observed on 31 October from the southeast quadrant of the Sun.

Coronagraph imagery showing the CME that came from the large filament eruption observed on 3 November from the northwest quadrant of the Sun. This was a partial halo CME.