LAUSR

Solar flare activity is characterized by different classification systems, both in optical and X-ray ranges. The most generally accepted classifications of solar flares describe important parameters of flares such as the maximum of brightness of the flare in the optical range – $$H_{\alpha }$$ H α flare class (change from F to B), area of the flare in $$H_{\alpha }$$ H α (change from S for areas less than 2 square degrees to 4 for areas more than 24.7 square degrees) and the maximum amplitude of the soft X-ray (SXR)-flux in the band 0.1–0.8 nm ( $$F_{0.1-0.8}^{\mathrm{max}}$$ F 0.1 - 0.8 max ) – X-ray flares of classes from C to X. A new classification parameter of solar flares is proposed here – the X-ray index of flare XI, based on GOES measurements of solar radiation in the SXR-range. The XI-index has a clear physical interpretation associated with the total flare energy in the SXR-range. XI is easily calculated for each flare with the use of available GOES data. The XI-index can be used along with other geoeffective parameters of Solar activity to assess both flares and coronal mass ejections that are connected with them.