SOLAR EUV FLUX VARIATIONS IN 11-YEAR SOLAR-ACTIVITY CYCLE ACCORDING TO MEASUREMENTS ON-BOARD PROGNOZ SATELLITE SERIES, INTERBALL-1 AND ELECTRO SATELLITES DURING 1978-1997 PERIOD

The paper presents data on flux variations of ionizing EUV radiation f or wavelengths shorter than 130 nm and in L-alpha hydrogen line on the basis of measurements performed on-board a Russian Earth-orbiting and interplanetary spacecrafts in the period since 1978 to 1997. These da ta were received by using common heritage instrumentation installed on four PROGNOZ satellites, INTERBALL-1, PHOBOS, and the geosynchronous meteorological satellite ELECTRO. Though the time series of observatio ns is not continuous, it gives a possibility to estimate flux variatio ns in certain periods of time and during 11-year cycle. During quiet p eriods of solar activity (except for flares ) a level of diurnal varia tions is rather low, it being equal to about 3%. Radiation changes in L-alpha line from maximum to minimum in an 11-year of solar activity a chieves 200% and increases in the range of short waves. Data measured onboard the Russian satellites are compared with data obtained by Sola r Mesospheric Explorer.