Abstract The intensity of continua and emission lines which form the solar UV spectrum below 2100 Å is variable. Continua and emission lines originating from different layers in the solar atmosphere show a different degree of variability. Coronal emission lines at short wavelengths are much more variable than continua at longer wavelengths which originate in lower layers of the solar atmosphere. Typical time-scales of solar UV variability are minutes (flare induced), days (birth of active regions), 27 days (solar rotation), 11 years (solar cycle) and perhaps centuries, caused by long-term changes of the solar activity. UV intensity variations have been determined by either absolute irradiance measurements or by contrast measurements of plages vs. the quiet sun. Plages are the main contributor to the solar UV variability. Typical values for the solar UV variability over a solar cycle are: <1% at wavelengths longer than 2100 Å, 8% at 2080 Å (continuum), 20% at 1900 Å (continuum), 70% at H Lyα, 200% in certain emission lines 1200 < λ < 1800 Å and more than a factor of 4 in coronal lines λ < 1000 Å. Plage models predict the variable component of the solar UV radiation within ±50%. Absolute fluxes are known within ±30%. Several efforts are underway to monitor the solar UV irradiance with a precision better than a few percent over a solar activity cycle.


    Access

    Check access

    Check availability in my library

    Order at Subito €


    Export, share and cite



    Title :

    The variability of the sun's ultraviolet radiation


    Contributors:

    Published in:

    Publication date :

    1981-01-01


    Size :

    15 pages




    Type of media :

    Article (Journal)


    Type of material :

    Electronic Resource


    Language :

    English



    Extreme Ultraviolet Heliograms and the Sun'S Corona

    M. J. Koomen / J. D. Purcell / R. Tousey | NTIS | 1967


    Extreme ultraviolet heliograms and the sun's corona

    Koomen, M. J. / Purcell, J. D. / Tousey, R. | NTRS | 1967


    Extreme Ultraviolet Heliograms and the Sun'S Corona

    M. J. Koomen / J. D. Purcell / R. Tousey | NTIS | 1967


    Sun's seadrome

    Armstrong, E.R. | Engineering Index Backfile | 1950


    Photocathodes for the investigation of sun's short-wave radiation

    Shuba, Yu. A. / Sorokin, O. M. / Tyutikov, A. M. | NTRS | 1962