This weekend, sunspot AR2699 is directly facing Earth. At 1321 UT on Feb. 10th, the sunspot’s magnetic canopy erupted, producing a C4-class solar flare. Extreme UV radiation from the flare ionized the top of Earth’s atmosphere. This, in turn, caused a brief ‘brownout’ of shortwave radio signals over South America and the South Atlantic Ocean: map. Frequencies affected were below 10 MHz. Free: Solar Flare Alerts
A solar flare is an explosion on the Sun that happens when energy stored in twisted magnetic fields (usually above sunspots) is suddenly released. Flares produce a burst of radiation across the electromagnetic spectrum, from radio waves to x-rays and gamma-rays.
Scientists classify solar flares according to their x-ray brightness in the wavelength range 1 to 8 Angstroms. There are 3 categories: X-class flares are big; they are major events that can trigger planet-wide radio blackouts and long-lasting radiation storms. M-class flares are medium-sized; they can cause brief radio blackouts that affect Earth’s polar regions. Minor radiation storms sometimes follow an M-class flare. Compared to X- and M-class events, C-class flares are small with few noticeable consequences here on Earth.