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Solar Irradiance – The Incoming Side of Radiative Balance

Solar Irradiance – The Incoming Side of Radiative Balance. Greg Kopp. Laboratory for Atmospheric and Space Physics University of Colorado 1234 Innovation Dr., Boulder, CO 80303, USA Greg.Kopp@LASP.Colorado.edu. 4.0 Incoming Solar Radiation at TOA. Chapter lead: Raschke with Kopp

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Solar Irradiance – The Incoming Side of Radiative Balance

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  1. Solar Irradiance –The Incoming Side of Radiative Balance Greg Kopp Laboratory for Atmospheric and Space Physics University of Colorado 1234 Innovation Dr., Boulder, CO 80303, USA Greg.Kopp@LASP.Colorado.edu

  2. 4.0 Incoming Solar Radiation at TOA Chapter lead: Raschke with Kopp • 4.1 Uncertainties of Solar Constant Measurements • 4.2 Global/Seasonal Distribution • 4.3 Representation in Satellite Products • 4.4 Survey of Models

  3. 4.0 Incoming Solar Radiation at TOA Chapter lead: Raschke with Kopp • 4.1 Uncertainties of Solar Irradiance Measurements • It’s not constant • 4.2 Global/Seasonal Distribution • Global - Divide direct solar-pointed irradiance measurements by 4 • Seasonal - 6.6% variation; geometric; & sensitive to 11-year solar cycle • 4.3 Representation in Satellite Products • Total solar irradiances - continuous from 1978 onward • Solar spectral irradiances across spectrum from 2003 onward • 4.4 Survey of Models (Solar) • Address solar activity pretty well on short time scales • Do not address potential long-term fluctuations

  4. Solar Irradiance Is Linked With Solar Activity The “solar constant” isn’t.

  5. Solar and Anthropogenic Climate Signals from Judith Lean, NRL GISS Land+Ocean Global Temperature monthly means El Nino La Nina volcanic aerosols omitting solar forcing  .. poorer tracking of centennial variations .. higher sensitivity to GHGs http://data.giss.nasa.gov/ greenhouse gases industrial aerosols

  6. None of these instruments is calibrated end-to-end for irradiance. TSI Climate Record ~30 Years Young Data are readily available! (And have very few parameters)

  7. TSI Record Has Relied on Continuity

  8. Future Needs: TSI – Accuracy and Stability • Performance Requirements • Accuracy 0.01% (1 ) • Stability 0.001%/yr (1 ) • Noise 0.001% (1 )

  9. Total Irradiance Monitor (TIM) Major Advances • Nickel-Phosphorous (NiP) black absorber provides high absorptivity and radiation stability • Phase sensitive detection at the shutter fundamental frequency reduces noise • Optical design reduces effects of scattered light and diffraction

  10. Summary of Stated Instrument Accuracies Uncertainties are 1-

  11. TSI Instrument Uncertainties & Intra-Instrument Variations Uncertainties are 1-

  12. Diffraction Can Erroneously Change Signal • All instruments except TIM put primary aperture close to the cavity Sunlight Sunlight View-Limiting Aperture Precision Aperture Precision Aperture View-Limiting Aperture NIST calculates this to be a 0.13% effect in the ACRIM instruments, and it is not corrected Failure to correct for light diffracted into cavity erroneously increases signal Failure to correct for light diffracted out of cavity erroneously decreases signal

  13. Scatter Can Erroneously Increase Signal • All instruments except TIM put primary aperture close to the cavity Sunlight Sunlight View-Limiting Aperture Precision Aperture Precision Aperture View-Limiting Aperture Additional light allowed into instrument can scatter into cavity Majority of light is blocked before entering instrument

  14. NIST calculates diffraction should lower these results. TSI Instrument Uncertainties & Intra-Instrument Variations

  15. TSI Instrument Uncertainties – With Diffraction Correction Correction not yet approved or applied by ACRIM or ERBE Teams

  16. Address Applied Power: Trap Diode Power Comparison • This was a recommendation from the 2005 TSI Accuracy Workshop • NIST and LASP performed optical power comparisons between a trap diode transfer standard and a ground-based TIM • Applying solar power levels with the TIM in vacuum • NPL has done similar power comparisons before, but in air Brewster vacuum window TSI instrument shutter stabilized laser 70 mW beamsplitter (0.2%) <1 mW trap diode This is an optical power measurement, not irradiance

  17. NIST Power Comparison Setup • Coherent Verdi V10 532-nm laser • CRI laser stabilizer • Spatial filter (pinhole) • Beam monitor to control stabilizer • Uniblitz shutter to modulate laser beam • Dual beam splitters (500:1) give parallel beam to trap diode • TIM gets primary beam • in vacuum behind Brewster window • on translation stage • Trap diode monitors low-power beam • on same translation stage as TIM • has 8 mm aperture Thanks to Allan Smith and Joe Rice!

  18. Measure Power Level for All Four TIM Cones • The TIM Witness Unit measures laser power lower than NIST by 0.12% • This is an end-to-end optical power measurement • Cone-to-cone variability spread is 230 ppm • Measurements are consistent • Need to verify some factors • Non-equivalence for DC subtraction method, heater resistances, gain

  19. No flight TSI instrument has been calibrated end-to-end First facility to measure irradiance at desired accuracies at solar power levels in vacuum TSI Radiometer Facility Measures Irradiance

  20. NIST calculations for ACRIM aperture diffraction indicate all three ACRIMinstrumentsshould have lower TSI values by 1.8 W/m2 • ERBE should also be lowered • NIST aperture area calibrations may indicate even larger differences Radiative Flux: SORCE TIM Indicates Lower TSI Value Fundamental discovery that the TSI is ~1361 W/m2, not 1366 W/m2 (TIM). SORCE/TIM result motivated detailed examination by NIST and TSI community. • TIMTSIis 4.7 W/m2 lower than other recent measurements • NIST radiometric power comparisons with ground-based TIM do not indicate an error with the TIMTSI value

  21. Solar Total Irradiance Measurement Summary • Continuous and overlapping measurements are critical in maintaining a long term data record. • Critical for climate • Useful for inputs to solar and atmospheric models • NIMBUS7 ERB (1978 - 1993) • SMM ACRIM I (1980 - 1989) • ERBS ERBE (1984 - 2003) • UARS ACRIM II (1991 - 2001) • SOHO VIRGO (1996 - ) • ACRIMSat ACRIM III (1999 - ) • SORCE TIM (2003 - ) • PICARD PMO6 & SOVAP (2008 - ) • Glory TIM (2008 - ) • NPOESS TIM (2013 - ) ? ?

  22. Solar Variability Depends on Wavelength SORCE and TIMED provide the first ever daily measurements of solar spectrum variations throughout the X-ray, UV, visible, and NIR

  23. Solar Cycle Variationfor the downward trend, 1991 to 1997. The uncertainty in these ratios are larger since they invoke knowledge of the instrument sensitivity over a time period of 5 years. Solar Variability on Different Time Scales 27-Day Variationfor a single solar rotation period. Other time periods show more or less variation, but with the same general spectral shape. Data from UARS/SOLSTICE

  24. Also Need Solar Spectral Irradiance Inputs Near UV, visible, near infrared radiation affect surface and ocean processes Chemistry Climate Models Need SSI GISS GCM [Rind et al., 2004; Shindell et al., 2006] NCAR WACCM [Marsh et al., 2007] HAMMONIA [Schmidt and Brasseur, 2006] CMAM [Beagley et al., 1997] [Adapted from P. Pilewskie, Solar Physics, 2005]

  25. Atmospheric Heating Rates Depend on Spectral Irradiances

  26. Total Irradiance Monitor (TIM) TIM SIM Spectral Irradiance Monitor (SIM) 200 – 2000 nm TIMED EGS SOLSTICE SOLar STellar Irradiance Comparison Experiment (SOLSTICE) 120 – 300 nm XUV Photometer System (XPS) 1 – 34 nm XPS XUV EUV UV IR SORCE and TIMED Measure Irradiance Across Spectrum • Solar irradiance measurements since March 2003 • Nearly complete solar spectral coverage

  27. Solar Spectral Irradiance Measurement Summary • GOES XRS (1975 - ) • POES SBUV (1985 - ) • SME (1981 - 1990) • UARS (1991 - 2005) • GOME (1995 - ) • SOHO SEM (1996 - ) • SOHO VIRGO SPM (1996 - ) • SNOE (1998 - 2003) • TIMED (2001 - 2008) • SORCE (2003 - 2009) • GOES EUVS (2006 - ) • SDO EVE (2008 - 2013+) • NPOESS SIM (2013 - ) ?

  28. Solar Spectral Irradiance Time Series Increasing Wavelength • GOES X-Ray Sensor (XRS) - since 1975 • 2 channels: 0.05 to 0.4 nm and 0.1 to 0.8 nm at 0.512-s cadence • TIMED and SORCE XUV Photometer System (XPS) - since 2001 • 8 filter bandpasses from 0.1 to 34 nm and Ly- • SOHO Solar Extreme Ultraviolet Monitor (SEM) - since 1996 • 2 filter and transmission grating bandpasses 0.1 to 50 nm & 30.4 nm (He II) • SNOE Solar X-ray Photometer (SXP) - 1998 to 2003 • 5 filter bandpasses from 2 to 35 nm • TIMED EUV Grating Spectrograph (EGS) - since 2001 • 25 to 200 nm with 0.4 nm resolution • Solar Mesospheric Explorer (SME) - 1981 to 1990 • 115 to 302 nm • UARS and SORCE SOLSTICE - since 1991 • 115 to 320 nm with 0.1-0.2 nm resolution, 0.5% precision, daily spectra • UARS Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) - 1991 to 2005 • 115 to 410 nm w/ 1 nm resolution, daily cadence, 2% precision • POES SBUV/2 - since 1985 • 160 to 400 nm with 1.1 nm resolution, daily cadence includes Mg II core to wing • ERS2 Global Ozone Monitoring Experiment (GOME) - since 1995 • 240-400 nm, Mg II core to wing • SOHO VIRGO SPM - since 1996 • 3 filter bandpasses (402, 500, 862 nm) with 5 nm resolution, 1-min cadence • ENVISAT SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) - since 2002 • 240 to 2380 nm with 0.2 to 1.5 nm resolution • SORCE SIM - since 2003 • 200 to 2700 nm with 0.25-33 nm resolution, 4 spectra/day

  29. Models Do Not Replace Measurements Can indirect measurements or models compensate for a lack of direct observations? • Models using sunspot area and faculae account for most of short-term variability • No model addresses potential long-term changes

  30. Decompositions Based on Images Indicate Solar Causes Fontenla, White, Fox, Avrett, Kurucz., ApJ518, pp. 480-499, 1999 • Determine distribution and evolution of solar features from PSPT images • Use a semi-empirical model to synthesize the intensity from each feature • Combine the intensities to compute an irradiance spectrum

  31. The TSI Climate Data Record Currently Relies on Continuity 0.9K 0.1K • Summary • Current instrument stabilities are adequate for discerning short-term climate sensitivity with continuity • Accuracies to maintain long-term record despite potential data gap have not yet been achieved • Ground-based calibration facilities will benefit future instruments and data record accuracy • The TIM’s 1361 W/m2 remains our best knowledge of TSI 0.7K Empirical Reconstruction courtesy Judith Lean, NRL

  32. Measurements of Solar Irradiance: Conclusions • Solar Irradiance Uses • Total solar irradiance used for climate sensitivity studies by extending 30-year data record and understanding solar variability • Solar spectral irradiance measurements needed to model Earth’s atmospheric response and solar variability • Absolute accuracy of radiative balance • With TIMED, SORCE, and GOES we for the first time have complete and continuous spectral irradiance coverage... • ... and future EUV spectral irradiances from SDO and GOES-R will provide higher spectral resolution inputs for modeling and forecasting

  33. Historical Solar Irradiance Measurements Solar Spectral Irradiance • Visible: GOME, SORCE SIM • MUV: Nimbus, SBUV, SME, UARS, GOME • FUV: OSO, AE-E, SME, UARS, SORCE • XUV/EUV: SOLRAD, AE-E, GOES, SNOE, TIMED SEE Total Solar Irradiance • NIMBUS 7 ERB • SMM ACRIM I • UARS ACRIM II • ERBS ERBE • SOHO VIRGO • ACRIMSAT ACRIM III • SORCE TIM

  34. LISIRD LASP Interactive Solar Irradiance Datacenter http://lasp.colorado.edu/lisird/

  35. Solar Irradiance Is A Boundary Condition based on Kiehl and Trenberth 1997 changes based on Coupled Climate System Models presented by W. Collins (SORCE Sci. Mtg 2006)

  36. Composites Rely on Continuity and Stability Two primary TSI composites differ by 40 ppm/yr caused by 2 years of marginal quality data – not even a gap! ?

  37. Future Irradiance Measurements

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