Two M-class flares were recorded on the Sun on October 6, one of which caused a coronal mass ejection (CME) aimed at Earth. According to current forecasts, the plasma cloud could reach the planet on October 9 and cause a weak to moderate geomagnetic storm.
Solar activity reached a moderate level after the active region AR4549, located near the center of the visible solar disk, produced two M-class flares within about two hours. The Australian Space Weather Forecast Center reported events of M1.4 at 06:10 UTC and M1.9 at 08:05 UTC on October 6. The US NOAA center determined the latter as M1.8, which is a small difference related to the processing of observations.
Class M means a moderately strong solar flare. The X-ray flare scale includes categories A, B, C, M and X, with each subsequent level being ten times more powerful than the previous one. Therefore, the events of October 6 are significant, but do not fall into the most powerful category X.
Plasma cloud moves towards Earth
The M1.4 eruption has attracted particular attention. Observations show that it was accompanied by a coronal mass ejection, in which a huge amount of plasma and magnetic field leaves the solar corona.
The European Solar Influences Data Analysis Center (SIDC) reported a weak halo CME, recorded by the LASCO coronagraph on the SOHO space observatory. Preliminary estimates give a projected speed of about 560 km/s, and the cloud has an Earth-directed component. It is expected to reach the planet around October 9.
However, this does not automatically mean a strong magnetic storm. The effect on the Earth's magnetosphere depends not only on the speed and density of the plasma, but also on the orientation of the magnetic field in the CME itself. Its north-south component is particularly important. If it is oriented sufficiently southward upon arrival, the interaction with the Earth's magnetic field may become more effective and geomagnetic activity may increase.
As of October 7, the UK Met Office is forecasting probable conditions for a G1, or weak geomagnetic storm, and a possibility of a G2, a moderate storm, on October 9. The center explicitly states that no other Earth-directed CMEs are expected at this time.
What does a G1 or G2 magnetic storm mean
NOAA's scale for geomagnetic storms ranges from G1 to G5. G1 is the lowest level, while G2 means a moderate storm. Under such conditions, temporary disruptions to radio communications and satellite systems are possible, as well as changes in the operation of electrical grids in high latitudes. The most visible effect is usually an expansion of the area where auroras can be observed.
The Met Office expects the aurora zone to expand to lower latitudes around the arrival of the CME on 9 October, although how far south it will reach will only be clear once the actual characteristics of the plasma flow have been measured.
Active region AR4549 remains under observation
The source of both flares, AR4549, is a magnetically complex solar region. NOAA reports that it continues to grow and form new magnetic flux, having produced almost all of the significant activity on the visible side of the Sun over the past 24 hours.
Forecasts leave the possibility of further M-class flares in the coming days and a smaller chance of a stronger event. However, this does not necessarily mean that a powerful eruption is imminent. Such forecasts assess the probability according to the magnetic structure of active regions, but the exact timing and strength of an individual solar eruption cannot be reliably predicted days in advance.
Therefore, the main event that experts are currently monitoring is the arrival of the plasma cloud on October 6. According to current models, October 9 is the most likely day for increased geomagnetic activity, and so far the forecast is for a weak to moderate magnetic storm, not an extreme event.