Lyman Decrements of Neutral Hydrogen Lines in the Spectrum of the Sun Based on SDO/EVE Observations. Variations During the 24-th Solar Cycle and in Individual Flares of Classes M and X

Abstract

Data from satellite observations of fluxes in Lyman series lines and their relative variations, both during the 24-th cycle and in individual class M and X flares, are analyzed. The decrement D1 (D1 = F(Lα)/F(Lβ)) has varied over the 24-th activity cycle by roughly 25% from its maximum values to minimum values during 2014, when there was a secondary maximum in the 24-th cycle according to the main indices. Decrement D2 (D2 = F(Lγ)/F(Lβ)) varies by roughly 10% during the cycle, and decrement D3 (D3 = F(Lδ)/F(Lβ)), by roughly 5% during the cycle. D1, D2, and D3 also vary during the cycle at smaller amplitudes with periods analogous to the periods of the quasi-biennial variations of the main activity indices. In flares of x-ray classes from M to X the variations of the Lyman decrements range from 2 to 20%, with the variations in the decrements being larger on the average for flares with higher energies in the soft x-ray range.