A flux of EUV emission measured on-board the “CORONAS” artificial satellites near minimum and maximum of the 23rd cycle of solar activity Original Research Article

The paper presents data on ionizing short-wave UV-emission of the Sun in a wave-range λ ⩽ 130 nm measured on-board the CORONAS-I and CORONAS-F satellites. There were obtained absolute values of solar flux emission in the spectrum range λ ⩽ 130 nm and the band near H Lα hydrogen line on-board both satellites. Measurements on-board the CORONAS-I satellite coincided with a phase near the minimum of solar activity (F10.7 = 80–100). In the period from March to June of 1994 the solar flux was equal on the average to 7.5 erg cm−2 s−1 for λ ⩽ 130 nm and the intensity of emission in H Lα was equal to (5.5–6.1) erg cm−2 s−1. The measurements on-board the CORONAS-F were performed near the maximum of solar activity (F10.7 = 143–279). Emission intensity in H Lα line was about 6.8 –8.2 erg cm−2 s−1 and in the wave-range λ ⩽ 130 nm it was equal on the average to 11–13 erg cm−2 s−1. EUV measurements are in agreement with the data obtained on-board UARS satellite and with the results of ionospheric measurement of E-layer critical frequencies. These measurements agree with data of contemporary models as well. A lot of flares including bright ones were observed. The measurement data of a bright flare of X-ray class X5.3 on 25.05.2001 are given. The paper presents the results of comparison between the CORONAS-F data and the X-ray fluxes in waveband 0.1–0.8 nm (GOES). This comparison demonstrated that X-ray emission measured on-board the GOES spacecraft and measured due to SUVR instrument (with filters in wave-range <12 nm) changed almost synchronously in the ranges 0.1–0.8 and 0.1–12 nm. The data measured due to VUSS showed that EUV emission appeared a few minutes (1–13) before X-ray emission. Apparently it evidences that at first a flare begins in the chromosphere and then a heating area is spreading higher. Solar emission increases by ∼20–30% in the range λ < 130 nm, and only by 8–10% in EUV range. Changes of extreme ultraviolet (EUV) solar flux were registered during the annular solar eclipse of May 31, 2003, when the CORONAS-F satellite thrice intersected a zone of the solar eclipse.