Greg Kopp, p. 126 June 2007Solar Irradiance Solar Irradiance – The Incoming Side of Radiative Balance Laboratory for Atmospheric and Space Physics University of Colorado 1234 Innovation Dr., Boulder, CO 80303, USA Greg Kopp

Greg Kopp, p. 226 June 2007Solar Irradiance 4.0Incoming Solar Radiation at TOA Chapter lead: Raschke with Kopp 4.1Uncertainties of Solar Constant Measurements 4.2Global/Seasonal Distribution 4.3Representation in Satellite Products 4.4Survey of Models

Greg Kopp, p. 326 June 2007Solar Irradiance 4.0Incoming Solar Radiation at TOA Chapter lead: Raschke with Kopp 4.1Uncertainties of Solar Irradiance Measurements –It’s not constant 4.2Global/Seasonal Distribution –Global - Divide direct solar-pointed irradiance measurements by 4 –Seasonal - 6.6% variation; geometric; & sensitive to 11-year solar cycle 4.3Representation in Satellite Products –Total solar irradiances - continuous from 1978 onward –Solar spectral irradiances across spectrum from 2003 onward 4.4Survey of Models (Solar) –Address solar activity pretty well on short time scales –Do not address potential long-term fluctuations

Greg Kopp, p. 426 June 2007Solar Irradiance Solar Irradiance Is Linked With Solar Activity The “solar constant” isn’t.

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

Greg Kopp, p. 626 June 2007Solar Irradiance TSI Climate Record ~30 Years Young Data are readily available! (And have very few parameters) None of these instruments is calibrated end-to- end for irradiance.

Greg Kopp, p. 726 June 2007Solar Irradiance TSI Record Has Relied on Continuity

Greg Kopp, p. 826 June 2007Solar Irradiance Future Needs: TSI – Accuracy and Stability Performance Requirements –Accuracy0.01% (1  ) –Stability0.001%/yr (1  ) –Noise0.001% (1  )

Greg Kopp, p. 926 June 2007Solar Irradiance 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

Greg Kopp, p June 2007Solar Irradiance Summary of Stated Instrument Accuracies Uncertainties are 1- 

Greg Kopp, p June 2007Solar Irradiance TSI Instrument Uncertainties & Intra-Instrument Variations Uncertainties are 1- 

Greg Kopp, p June 2007Solar Irradiance Diffraction Can Erroneously Change Signal View-Limiting Aperture Precision Aperture View-Limiting Aperture Precision Aperture Sunlight Failure to correct for light diffracted into cavity erroneously increases signal All instruments except TIM put primary aperture close to the cavity Failure to correct for light diffracted out of cavity erroneously decreases signal NIST calculates this to be a 0.13% effect in the ACRIM instruments, and it is not corrected

Greg Kopp, p June 2007Solar Irradiance Scatter Can Erroneously Increase Signal View-Limiting Aperture Precision Aperture View-Limiting Aperture Precision Aperture Sunlight Additional light allowed into instrument can scatter into cavity All instruments except TIM put primary aperture close to the cavity Majority of light is blocked before entering instrument

Greg Kopp, p June 2007Solar Irradiance TSI Instrument Uncertainties & Intra-Instrument Variations NIST calculates diffraction should lower these results.

Greg Kopp, p June 2007Solar Irradiance TSI Instrument Uncertainties – With Diffraction Correction Correction not yet approved or applied by ACRIM or ERBE Teams

Greg Kopp, p June 2007Solar Irradiance stabilized laser Brewster vacuum window beamsplitter (0.2%) TSI instrument trap diode 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 shutter 70 mW <1 mW This is an optical power measurement, not irradiance

Greg Kopp, p June 2007Solar Irradiance NIST Power Comparison Setup Coherent Verdi V 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!

Greg Kopp, p June 2007Solar Irradiance 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

Greg Kopp, p June 2007Solar Irradiance TSI Radiometer Facility Measures Irradiance No flight TSI instrument has been calibrated end-to-end First facility to measure irradiance –at desired accuracies –at solar power levels –in vacuum

Greg Kopp, p June 2007Solar Irradiance Radiative Flux: SORCE TIM Indicates Lower TSI Value Fundamental discovery that the TSI is ~1361 W/m 2, not 1366 W/m 2 (TIM). TIM TSI is 4.7 W/m 2 lower than other recent measurements NIST radiometric power comparisons with ground-based TIM do not indicate an error with the TIM TSI value SORCE/TIM result motivated detailed examination by NIST and TSI community. NIST calculations for ACRIM aperture diffraction indicate all three ACRIM instruments should have lower TSI values by 1.8 W/m 2 ERBE should also be lowered NIST aperture area calibrations may indicate even larger differences

Greg Kopp, p June 2007Solar Irradiance 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 ( ) SMM ACRIM I ( ) ERBS ERBE ( ) UARS ACRIM II ( ) SOHO VIRGO ( ) ACRIMSat ACRIM III ( ) SORCE TIM ( ) PICARD PMO6 & SOVAP ( ) Glory TIM ( ) NPOESS TIM ( ) ? ?

Greg Kopp, p June 2007Solar Irradiance 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

Greg Kopp, p June 2007Solar Irradiance 27-Day Variation for a single solar rotation period. Other time periods show more or less variation, but with the same general spectral shape. Solar Cycle Variation for the downward trend, 1991 to 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 Data from UARS/SOLSTICE

Greg Kopp, p June 2007Solar Irradiance Also Need Solar Spectral Irradiance Inputs 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] Near UV, visible, near infrared radiation affect surface and ocean processes [Adapted from P. Pilewskie, Solar Physics, 2005]

Greg Kopp, p June 2007Solar Irradiance Atmospheric Heating Rates Depend on Spectral Irradiances

Greg Kopp, p June 2007Solar Irradiance SORCE and TIMED Measure Irradiance Across Spectrum Solar irradiance measurements since March 2003 Nearly complete solar spectral coverage XUV Photometer System (XPS) 1 – 34 nm XPS Spectral Irradiance Monitor (SIM) 200 – 2000 nm SIM SOLar STellar Irradiance Comparison Experiment (SOLSTICE) 120 – 300 nm SOLSTICE TIM Total Irradiance Monitor (TIM) XUVEUVUVIR EGS TIMED

Greg Kopp, p June 2007Solar Irradiance Solar Spectral Irradiance Measurement Summary GOES XRS ( ) POES SBUV ( ) SME ( ) UARS ( ) GOME ( ) SOHO SEM ( ) SOHO VIRGO SPM ( ) SNOE ( ) TIMED ( ) SORCE ( ) GOES EUVS ( ) SDO EVE ( ) NPOESS SIM ( ) ?

Greg Kopp, p June 2007Solar Irradiance Increasing Wavelength Solar Spectral Irradiance Time Series GOES X-Ray Sensor (XRS) - since 1975 –2 channels: 0.05 to 0.4 nm and 0.1 to 0.8 nm at 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) 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) to 1990 –115 to 302 nm UARS and SORCE SOLSTICE - since 1991 –115 to 320 nm with nm resolution, 0.5% precision, daily spectra UARS Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) 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 – 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 nm resolution, 4 spectra/day

Greg Kopp, p June 2007Solar Irradiance 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

Greg Kopp, p June 2007Solar Irradiance Decompositions Based on Images Indicate Solar Causes Fontenla, White, Fox, Avrett, Kurucz., ApJ 518, pp , 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

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/m 2 remains our best knowledge of TSI The TSI Climate Data Record Currently Relies on Continuity courtesy Judith Lean, NRL Empirical Reconstruction 0.1K 0.9K 0.7K

Greg Kopp, p June 2007Solar Irradiance 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

Greg Kopp, p June 2007Solar Irradiance Historical Solar Irradiance Measurements Total Solar Irradiance –NIMBUS 7 ERB –SMM ACRIM I –UARS ACRIM II –ERBS ERBE –SOHO VIRGO –ACRIMSAT ACRIM III –SORCE TIM 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

Greg Kopp, p June 2007Solar Irradiance LISIRD LASP Interactive Solar Irradiance Datacenter

Greg Kopp, p June 2007Solar Irradiance Solar Irradiance Is A Boundary Condition based on Kiehl and Trenberth 1997changes based on Coupled Climate System Models presented by W. Collins (SORCE Sci. Mtg 2006)

Greg Kopp, p June 2007Solar Irradiance Two primary TSI composites differ by 40 ppm/yr caused by 2 years of marginal quality data – not even a gap! Composites Rely on Continuity and Stability ?

Greg Kopp, p June 2007Solar Irradiance Wavelength Range Past Measurements SORCE MeasurementsFuture Measurements TSI (all s) ERBE, ACRIM (ongoing), SOHO VIRGO (ongoing) Glory, PICARD Vis-NIR ( nm) SCIAMACHY (ongoing) Future unknown (NPOESS TSIS descoped) FUV-MUV-NUV ( nm) NOAA SBUV (ongoing), UARS SOLSTICE & SUSIM NOAA SBUV (no FUV though) EUV ( nm) GOES, SOHO SEM, TIMED SEE (all ongoing) SDO EVE GOES Future Irradiance Measurements