Abstract Empirical models which can provide physical insights to the origins of solar UV irradiance variations are discussed. Calculations using the WDC/NOAA plage records and independently measured UV plage contrasts show that bright, contiguous active regions cause much of the observed variability in the full disc UV irradiances over time scales of solar rotation (≈ 27 days) and active region evolution (≈ 4 to 9 months), but can account for only about half variability observed over the 11-year solar cycle. This is demonstrated for the HI Lyman α emission, the 205 nm emission and also for the spectrally integrated facular emission which causes variations in the total radiative output. These results confirm the need for an additional irradiance component whose magnitude is at least as great as that associated with variations in active region emission alone, and which affects the solar atmosphere from the base of the photosphere to heights beyond the chromosphere on an 11-year time scale. Possible scenarios for this additional irradiance component are considered.
Modelling solar UV irradiance variability
Advances in Space Research ; 8 , 7 ; 85-94
1989-01-01
10 pages
Article (Journal)
Electronic Resource
English
Modelling of total solar irradiance variability: An overview
Elsevier | 1989
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