Solar Cycle Dependence of Solar UV Irradiance

Details Solar Cycle Dependence of Solar UV Irradiance Solar Cycle Dependence of Solar UV Irradiance

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmgc31b0344f&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #GC31B-0344

Physics

7536 Solar Activity Cycle (2162), 7537 Solar And Stellar Variability (1650), 7538 Solar Irradiance, 7549 Ultraviolet Emissions, 7594 Instruments And Techniques

Scientific paper

For the past 30 years during solar cycles 21, 22, and 23, the solar ultraviolet (UV) spectral irradiance has been measured by a series of several long-term space-based experiments, including the NOAA SBUV/SBUV2 series, the UARS experiments (SOLSTICE and SUSIM), and the instruments aboard SORCE. Accurate, absolutely calibrated spectral irradiances can be difficult to obtain from these daily measurements because the changing optical characteristics of measuring instruments are often uncertain, especially over the long-term. Accordingly, the resulting UV irradiance data can sometimes contain unwanted instrumental trends. These solar UV irradiance time series are dominated by two periodicities: solar rotation (~27 days) and solar activity (~11 years). They have also been shown to correlate very well with indices of solar activity, particularly the Mg~II core-to-wing ratio. The relative variation of the solar UV ranges from nearly a factor of two at Ly-α, about 10% at 200nm, to less than 1% above 320 nm. For the long wavelength portion of the UV spectrum, above about 263~nm, the long-term accuracy is typically comparable to the solar cycle variation. However, because the level of UV irradiance increases strongly with wavelength, most of the variation in total UV irradiance is provided by wavelengths above 250~nm. Using the latest versions of the various solar UV irradiance time series, the level of agreement of the relative changes of the various data sets is examined. From this, an assessment may be made as to the accuracy of the irradiances which is compared with the reported uncertainties. Using the correspondence with the solar Mg~II index, the solar cycle variation based on the available maximum to minimum or minimum to maximum transitions is analyzed to reveal differences among the three solar cycles.

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