Solar flares are classified using the X-ray brightness (see an explanation here), and "X class" flares are the strongest. The sunspot and magnetic active region complex that produced many M-class and X-class flares last month is back, and the EVE "flare-ometer" is hitting the red zone again.
EVE measures irradiance in the extreme ultraviolet (EUV), which are wavelengths slightly less energetic than X-rays. EUV variations in flux have a direct impact on the Earth's atmosphere and ionosphere, so EVE's measurements are essential for space weather forecasts.
When combined with HMI and AIA, SDO is able to capture the magnetic structure and dynamics of space weather processes.
