Variations of Solar EUV Radiation Fluxes in Hydrogen Lines from Observations by the TIMED Satellite in Cycle 23 and by SDO/EVE in Cycle 24

Abstract

The fluxes in the spectral lines of the Lyman series and their variations in solar cycles 23 and 24 are analyzed. They are shown to vary differently with different solar activity throughout the 11-year cycle: the flux in line L_α (λ = 121.6 nm) decreases by about 40% of its magnitude at the activity maximum, and the greatest decrease (by 60–70%) is observed for the flux in line L_β (λ = 102.57 nm). It is shown for cycle 23 (TIMED observations) that both the fluxes and the half-widths of the spectral line profiles change noticeably depending on the cycle phase, with an increase towards the cycle maximum. Comparative analysis shows that variations in the average annual intensities of the Lyman lines and the radiation flux at a wavelength of 10.7 cm (F_10.7) differ for cycles 23 and 24. This fact is attributable to the specificity of cycle 24 and its secondary maximum, which exceeds its primary maximum. Regression dependences are presented for the fluxes in the Lyman lines (based on the daily SDO/EVE measurements) on F_10.7, which allow high-accuracy reconstruction of the magnitudes of these fluxes for different levels of solar activity.