Spectral Solar Irradiance over Cycle 23 from Sunphotometers

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 06. 03. 2021 AGU Fall Meeting 2010, Paper GC 33 C-08, 15. December 2010 1

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 06. 03. 2021 AGU Fall Meeting 2010, Paper GC 33 C-08, 15. December 2010 2

SPM Characteristcs § The three-channel Filterradiometers (called psunphometers) provide spectral irradiance data at three wavelengths with a bandpass of about 5 nm 06. 03. 2021 AGU Fall Meeting 2010, Paper GC 33 C-08, 15. December 2010 3

SPM Database from VIRGO/SOHO The data cover a full solar cylce from Feb. 1996 until present 06. 03. 2021 AGU Fall Meeting 2010, Paper GC 33 C-08, 15. December 2010 4

Temperature dependence of sensitivity for SPMA 06. 03. 2021 AGU Fall Meeting 2010, Paper GC 33 C-08, 15. December 2010 5

Temperature dependence of sensitivity for SPMB 06. 03. 2021 AGU Fall Meeting 2010, Paper GC 33 C-08, 15. December 2010 6

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. 06. 03. 2021 AGU Fall Meeting 2010, Paper GC 33 C-08, 15. December 2010 7

Decompose TSI record to use as proxy for the cycle variation of RGB 06. 03. 2021 AGU Fall Meeting 2010, Paper GC 33 C-08, 15. December 2010 8

Now we have everything to build the function to be fitted to the data 06. 03. 2021 AGU Fall Meeting 2010, Paper GC 33 C-08, 15. December 2010 9

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: 06. 03. 2021 2. 563 (Smode + 0. 873 SSpot + 1. 383 SFaculae) AGU Fall Meeting 2010, Paper GC 33 C-08, 15. December 2010 10

Now correct SPMA and compare to SIM 06. 03. 2021 AGU Fall Meeting 2010, Paper GC 33 C-08, 15. December 2010 11

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. 06. 03. 2021 AGU Fall Meeting 2010, Paper GC 33 C-08, 15. December 2010 12

This presentation is available from ftp: //ftp. pmodwrc. ch/pub/Claus/AGU_Fall 2010/GC 33 C-08. ppt. Thanks 06. 03. 2021 AGU Fall Meeting 2010, Paper GC 33 C-08, 15. December 2010 13