What will occur on the Earth when a sunspot with the size of approximately 6.5 Earths begins to release successive X-class flares into space?
A wave of solar activity has put engineers and satellite operators and radio users back into an old position wait, gauge and plan brief outages of a speed that is truly at the speed of light. Several X-class flares were registered in the course of days with an X8.1 flare being termed as one of the strongest in a number of years. These bursts represent the most intense type of flaring of the Sun, which are not lasting at the time, but can have knock-on effects on communications and navigation networks that require there to be stable conditions at the upper end of the atmosphere.
It has been primarily caused by an abnormally prolific active area. The Met Office called sunspot region AR4366, which is magnetically complicated, having a beta-gamma-delta structure that allows high-energy eruptions to occur frequently. Its surface area has been monitored at approximately equal quantities to a few Earths and the forecasters have not only monitored the count of flares but also whether each eruption is accompanied by a coronal mass ejection (CME) the slower heavier cloud of charged particles and embedded magnetic fields that can more severely disturb the magnetic environment of earth.
The value of solar flares is that they change the ionosphere on the dayside side of the earth through their radiation. According to the Space Weather Prediction Center of the National Oceanic and Atmospheric Administration, these occurrences may lead to loss of signals in the high frequency bands of a substantial part of the sunlit hemisphere and interruptions can take a few minutes to several hours. To both aviation and maritime customers who use HF as a backup resilience mechanism, and those who use HF due to a difficult path such as a polar-route, even short drops can cause cascading effects in the form of rerouting, procedural modifications, or loss of contact.
A commonly used opening is a flare. The longer-tail risk is provided by CMEs which may be later and may miss, may clip or directly hit the Earth. Not all flares release one and not all CMEs move in a fashion that causes it to be geoeffective. The Met Office observed that although the rate of flares remained high, only a fraction of eruptions produced CMEs with some studies indicating that at least one might create a glancing strike with the geomagnetic conditions increasing to minor storm levels. The expansion of auroras distant of the poles is not so much due to the intensity of the flare as due to the magnetic orientation of the material that arrives there, in particular, long-lasting, southward-directed fields, which resonate well with the magnetosphere of the earth.
The bigger picture is that the Sun also has been through a recent solar maximum period in the last cycle, yet the aftershock can be vigorous. The falling phase of the total number of sunspots is what is described by the Met Office though emphasizing that it does not mean that there will not be any strong events. This period is becoming an engineering planning environment, and not a spectacle, by space-weather operations centres: a time when alerts, modelling and cross-sector coordination are put under stress, and infrastructure owners are once again re-examining assumptions of satellite drag, radio propagation and grid resilience.
It is possible that the same physics can also result in brighter auroras seen on the ground, in the event of convenient skies.
In the case of systems in orbit and on the surface, the lesson to be learned practically is more limited and technical: frequent X-class flares focus effort on the problem of radio blackouts, variability of the ionosphere and the geometry of any underlying CMEs which may exist, and on the discipline of operations of observing the Sun, just as we observe the weather.
