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My Interest in GLORY: Total Solar Radiation

My Interest in GLORY: Total Solar Radiation Claus Fröhlich Physikalisch-Meteorlogisches Observatorium Davos, World Radiation Center, CH 7260 Davos Dorf, Switzerland eMail: cfrohlich@pmodwrc.ch ; http://www.pmodwrc.ch Solar Radiometry: absolute accuracy, stability

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My Interest in GLORY: Total Solar Radiation

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  1. My Interest in GLORY: Total Solar Radiation Claus Fröhlich Physikalisch-Meteorlogisches Observatorium Davos, World Radiation Center, CH 7260 Davos Dorf, Switzerland eMail: cfrohlich@pmodwrc.ch; http://www.pmodwrc.ch • Solar Radiometry: absolute accuracy, stability • Understanding variability of solar irradiance GLORY Science Meeting 17-18 January 2006

  2. How Accurate are Space Radiometers Until the launch of SORCE and the operation of TIM we all thought that we have improved the uncertainty from the early time of HF and ACRIM I. The composite shows how small the variation is compared to the spread of the data. It shows also that the precision is much higher than the absolute accuracy which allows to construct such composite with overlapping measurements. GLORY Science Meeting 17-18 January 2006

  3. Uncertainty of PMO6V WRR/SI GLORY Science Meeting 17-18 January 2006

  4. Final values of VIRGO TSI at the Beginning of the Mission DIARAD is fully characterized and represents its own independent radiometric scale. However, some corrections due to time constant effects and the area have been determined since the first evaluation; they amount to an overall correction of + 447 ppm. With these corrections the final ‘first light’ data of VIRGO are very consistent (within about 300 pmm), although their tracing to SI is completely independent. GLORY Science Meeting 17-18 January 2006

  5. VIRGO Measurements: What do we learn? • Level-1 are corrected for all known effects (electrical calibration, temperature, S/C position, etc) • Level-1.8 needs to correct for degradation, early increase etc by solar exposure. Exposure dependent changes can be corrected by comparison with a less exposed radiometer of the same type. • Level-2 is the final product, which includes the comparison of the two different types on VIRGO. This has revealed non-exposure changes of DIARAD, which cannot be determined without comparison to PMO6V. GLORY Science Meeting 17-18 January 2006

  6. Comparison to TIM/SORCE VIRGO Measurements: Results Level-2 of VIRGO is a combination of the results of PMO6V and DIARAD level-1.8, the latter being corrected for non-exposure dependent sensitivity changes. By comparison with 1-year filtered ACRIM and more recently TIM data, the share of the corrections for each is determined. GLORY Science Meeting 17-18 January 2006

  7. Comparison of corrected TSI at times of ERBS GLORY Science Meeting 17-18 January 2006

  8. Conclusions for Solar Radiometry from Space • The differences between classical radiometers and TIM are still not resolved and the reason is unknown. • It does not seem to be due to aperture areas, as it was most likely during the early measurements of TSI from space. • The good agreement between PMO6V and DIARAD-L which have completely different ways to trace to SI, indicates that the VIRGO results are most probably close to the SI (within about 300 ppm). • There may still be a problem with the WRR/SI comparison: the WRR factor of PMO6-9 and 11 are of the order of 1.004258 and 1.002751, indicating that the characterized PMO6 radiometers are about 0.35% below the WRR. • The success of the WRR/SI comparison at NPL provides the basis for similar comparison with TIM and ACRIMs at NIST in the near future. GLORY Science Meeting 17-18 January 2006

  9. Total Solar Irradiance Variability • In order to get a reliable time series we need a composite. • One can just believe them and merge them. However, there are several known problems which need corrections. • We quickly go through and show how the PMOD composite is constructed • Comparison of the three composites GLORY Science Meeting 17-18 January 2006

  10. Comparison with Proxy Models • We can build a proxy model taking the sunspot, faculae and network into account. The sunspots by PSI, the faculae by MgIIst and the network by MgIIlt. • Cycle 23 shows some problems with the long-term – maybe instrumental or some influence of spots on MgII. GLORY Science Meeting 17-18 January 2006

  11. Conclusions for TSI Variability • The reconstructions using magnetograms are very successful, indicating that the solar-rotation and the 11-year-cycle variations are due to the magnetic fields related to activity. • The proxy models show, that the 11-year cycle is due to the network and not directly related to active region spots and faculae. • It seems difficult to correlate TSI with activity indices as SSN. GLORY Science Meeting 17-18 January 2006

  12. That’s it, thanks. The composite can be downloaded from: http://www.pmodwrc.ch/pmod.php?topic=tsi/composite/SolarConstant and the VIRGO data from: http://www.pmodwrc.ch/pmod.php?topic=tsi/virgo/proj_space_virgo GLORY Science Meeting 17-18 January 2006

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