New Delhi: On 30 August, at 20:02 UTC, the SIDC Sunspot Group 617 or NOAA Active Region 4199 erupted in a long-duration M2.7 flare, the second-highest category of solar flares. This resulted in a spectacular full-halo coronal mass ejection (CME), where magnetised plasma from the Sun is hurled outwards into interplanetary space. On encountering planets with a geomagnetic field, such as the Earth, this material from the Sun induces geomagnetic storming. According to the Solar Influences Data Analysis Centre (SIDC), operated by the Royal Observatory of Belgium, the CME should result in a major or severe geomagnetic storm.
SWPC alert and forecast of the Geomagnetic Storm.
According to the SIDC forecast from 31 August, “Active conditions can be expected for today and up to major storm conditions tomorrow when the CME from 30 August is expected to arrive.” The CME will pile on to a high speed stream (HSS) from a coronal hole aimed straight at the Earth. According to the latest forecast by the Space Weather Prediction Centre (SWPC), operated by the US National Oceanic and Atmospheric Administration (NOAA), “Mildly enhanced conditions are expected for most of 01 Sep under negative polarity CH HSS influences. Stronger enhancements are likely late on 01 Sep through most of 02 Sep with the anticipated arrival of the 30 Aug asymmetric full-halo CME. Enhanced conditions are likely to continue on 03 Sep.”
Uncertainty in forecasts
While both SIDC and NOAA agree that the CME will strike the Earth on 1 September, the forecasts for the strength of the geomagnetic storm varies slightly, with SIDC predicting a stronger impact. According to the UK Met office, “G2-G3 (Moderate to Strong) Geomagnetic storms likely Days 1-2 with a chance of G4 Severe storm.” According to the forecast of the South African National Space Agency (SANSA), “Geomagnetic conditions are anticipated to range from quiet to G2/Moderate storm levels, with a slight chance of reaching G3/Strong storm levels due to the anticipated CME arrival.” Incidentally, the Carrington Event, the most powerful solar storm in recorded history, occurred between 1 and 2 September, 1859.