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EUV flux variation during end of solar cycle 20 and beginning cycle 21, observed from AE‐C satellite
Author(s) -
Hinteregger H. E.
Publication year - 1977
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl004i006p00231
Subject(s) - extreme ultraviolet lithography , solar minimum , physics , flux (metallurgy) , astrophysics , sunspot , solar cycle 22 , satellite , solar cycle , atmospheric sciences , astronomy , optics , magnetic field , materials science , solar wind , quantum mechanics , metallurgy
Minimum levels of solar EUV fluxes appear to have occurred about 14 months before July 1976, the month designated as the start of Cycle 21 (minimum of monthly mean value of sunspot number, R Z ). The EUV minimum, observed by the EUVS experiment on AE‐C, occurred around 20 April 1975 under conditions of a spotless disk and of a simultaneous minimum in F 10.7 . Another rise of quiet‐disk EUV, observed a few months before July 1976, was found in the low‐excitation lines such as 584 Å He I and 1026 Å H Ly‐β. The transition‐region lines of Fe X at 174.5 and 177.2 Å showed a substantial gradual rise later, toward the end of 1976 and mainly in early 1977, when periods of spotless disk with simultaneously minimal F 10.7 <70 no longer existed. EUV fluxes for days of "high" activity (R Z >30 with F 10.7 >80) on different sides of the sunspot minimum show drastically different relations to F 10.7 .