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Spectral Solar Irradiance over Cycle 23 from Sunphotometers of VIRGO

This study analyzes the spectral solar irradiance data collected by the VIRGO sunphotometers to determine the variations over solar cycle 23. The data cover a full cycle from February 1996 until present. The results are compared to SIM/SORCE results at these wavelengths and conclusions are drawn.

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Spectral Solar Irradiance over Cycle 23 from Sunphotometers of VIRGO

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  1. Spectral Solar Irradiance over Cycle 23 from Sunphotometers of VIRGO on SOHO Claus Fröhlich PMOD/WRC CH 7260 Davos Dorf The Level-1 data are provided by the VIRGO Data Center. The data for this study were prepared in cooperation with Christoph Wehrli, which is gratefully acknowledged AGU Fall Meeting 2010, Paper GC33C-08, 15. December 2010

  2. Outline • VIRGO SPM Data description • How can we deduce a reasonable measure of the solar cycle variations from SPMB, the backup instrument • How to transform this information to the SPMA, the continuously exposed instrument • How do these results compare to the SIM/SORCE results at these wavelengths • Conclusions AGU Fall Meeting 2010, Paper GC33C-08, 15. December 2010

  3. SPM Characteristcs • The three-channel Filterradiometers (called psunphometers) provide spectral irradiance data at three wavelengths with a bandpass of about 5 nm AGU Fall Meeting 2010, Paper GC33C-08, 15. December 2010

  4. SPM Database from VIRGO/SOHO The data cover a full solar cylce from Feb.1996 until present AGU Fall Meeting 2010, Paper GC33C-08, 15. December 2010

  5. Temperature dependence of sensitivity for SPMA AGU Fall Meeting 2010, Paper GC33C-08, 15. December 2010

  6. Temperature dependence of sensitivity for SPMB AGU Fall Meeting 2010, Paper GC33C-08, 15. December 2010

  7. How to deal with degradation? For the time dependent dose we have three terms: m(t) for the irradiance, the next is the Boltzman factor and the third the recovery during the time between the exposure. AGU Fall Meeting 2010, Paper GC33C-08, 15. December 2010

  8. Decompose TSI record to use as proxy for the cycle variation of RGB AGU Fall Meeting 2010, Paper GC33C-08, 15. December 2010

  9. Now we have everything to build the function to be fitted to the data AGU Fall Meeting 2010, Paper GC33C-08, 15. December 2010

  10. Results of the fitting SPMB Tsi scaled for RED: 0.429 (Smode + 1.020 SSpot + 1.506 SFaculae) Tsi scaled for GREEN: 1.286 (Smode + 1.272 SSpot + 2.044 SFaculae) Tsi scaled for BLUE: 2.563 (Smode + 0.873 SSpot + 1.383 SFaculae) AGU Fall Meeting 2010, Paper GC33C-08, 15. December 2010

  11. Now correct SPMA and compare to SIM AGU Fall Meeting 2010, Paper GC33C-08, 15. December 2010

  12. Conclusions • The degradation correction are not yet optimal – it still needs to be improved • The correlation with decomposed TSI provides interesting insights in the differences and similarities of the three colours and TSI • All three channels are positively correlated with the solar cycle and their amplitudes are relative to TSI 0.50, 1.85 and 2.78 for RGB • The comparison with SIM is quite good in the blue, somewhat less in the red and different in the green. AGU Fall Meeting 2010, Paper GC33C-08, 15. December 2010

  13. This presentation is available from ftp://ftp.pmodwrc.ch/pub/Claus/AGU_Fall2010/GC33C-08.ppt. Thanks AGU Fall Meeting 2010, Paper GC33C-08, 15. December 2010

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