Richard C. Willson, Precision of the Long-term Total ... - Acrim.com

Precision of the Long-term Total Solar Irradiance DatabaseACRIM INSTRUMENT TEAMRoger S. Helizon, Jet Propulsion LaboratoryInstrument Scientistroger@simdac.jpl.nasa.govACRIM SCIENCE TEAMDr. Richard C. Willson, Columbia UniversityPrincipal Investigatoracrim@acrim.comDr. Alex Mordvinov, Head –Solar Activity LaboratoryInstitute Of Solar Terrestrial Physics, Irkutsk, RussiaCo-InvestigatorDr. James Hansen, Director – NASA/GISSCo-InvestigatorDr. Hugh S. Hudson – University of CA at BerkeleyCo-InvestigatorCALCON 2002 Richard C. Willson - Columbia University 1

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TSI/Solar Active Region feature correlationsMO WL 4/25/00 MO WL 5/19/00 MO WL 9/21/00 MO WL 3/29/01BBSO CaII K 10/12/01

Total Solar Irradiance Varies in Direct Proportion toSolar Magnetic ActivityCALCON 2002 Richard C. Willson - Columbia University 4

Climate Varies in Direct Proportion toSolar Magnetic Activity• Climate and solar activity variations during past 1000 years– Climate observationsProxy: agriculture, freezing rivers, glacier and sea ice growth/retreatDirect: temperature, ice and sea level measurements, δ 18 O(recent)– Solar activity observationsProxy: 14 C, 10 Be, aurora sightings, visible sunspotsDirect: Solar astronomy (recent)Figure credit: Jack EddyCALCON 2002 Richard C. Willson - Columbia University 5

Climate, Total Solar IrradianceAnd a Monitoring Strategy• Climate and TSI are positively correlated• Correlated through relationships with solar magnetic activity• Little Ice Age minima may have required only 0.25 % TSI decreases• Observational requirements:– Maintain precision small compared to 0.25 % on century length time scalesUncertainty of ambient temperature TSI sensors ~ 0.1 % in SIInstrument level precision can be ~ 5 ppm/yr– Overlap strategy required for TSI experimentsCALCON 2002 Richard C. Willson - Columbia University 6

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The Composite TSI Model Dilemma:Relate ACRIM1 and ACRIM2 using Nimbus7/ERB or ERBS ?CALCON 2002 Richard C. Willson - Columbia University 9

Comparison of Critical Operational Characteristics ofTotal Solar Irradiance ExperimentsContributing to the precision Long Term Climate DatabaseColorContribution to Observations Degrading Sub-optimal Optimal OptimumExperimentPIModeObservingFrequencyShutterCalibrationFrequencyElectricalCalibrationFrequencyDegradationCalibrationSolarPointedNimbus7/ERB1978 – 1993Quasi3 of 4 days5 min/LEO orbitNone 2 weeks None NoSMM/ACRIM11980 - 1989Yes 55 min/LEO orbit 1 min. cycle Continuous 3-fold redundantMonthlyYesERBS1984 - 2000No 5 min. every 14days30 sec. cycle 2 weeks None NoUARS/ACRIM21991 Yes 35 min/LEO orbit 1 min. cycle Continuous 3-fold redundantMonthlyYesSOHO/VIRGO1996 YesContinuousL1 PointOnce/day Continuous 2-fold redundantHiatus issuesYesACRIMSATACRIM3 2000 Yes 62 min/LEO orbit 1 min. cycle Continuous 3-fold redundantMonthlyYesCALCON 2002 Richard C. Willson - Columbia University 10

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Comparison of Nimbus7/ERB and ERBS ResultsCALCON 2002 Richard C. Willson - Columbia University 13

Reconciliation of trend difference betweenTSI Models using ERB and ERBS comparisonsComparison ExperimentModel trend between minima (%/decade)ACRIM_ERBACRIM_ERB_VIRGONimbus7/ERB 0.037 .044ERBS 0.004 .011Trend difference: 0.033 0.033δ ERB ACRIM2-1– δ ERBS ACRIM2-10.032 0.032• Changes in ERB/ERBS ratio between ACRIM1 and ACRIM2 comparison periodsequals difference in trend of TSI models to within computational uncertainty• Probable cause: uncorrected degradation of ERBS, relative to Nimbus7/ERB, duringactivity maximum of solar cycle 22• Possible reasons:– TSI sensors degrade faster during solar maxima due to enhanced shortwavelength fluxes– ERBS sensors may have been more prone to degradation than Nimbus7/ERB’sduring this period due to prior exposure historiesCALCON 2002 Richard C. Willson - Columbia University 14

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Optimum TSI Monitoring Strategy• Deploy redundant TSI monitors– Provides continuous TSI record for solar physics and climate– Provide at least 1 year overlap– Preferably multiple designs– Ambient temperature radiometers are most cost effective– Absolute uncertainty: 0.1 % adequate– Precision: 5 ppm/yr achievable using 3 sensor redundancy, ACR modality• Deploy cryogenic radiometer annually on shuttle– LHe temperature device with 0.01 % SI uncertainty– Shuttle flight using expendable cryogen is cost effective approach– Employ ‘GASCAN’ approach to minimize cost and maximize opportunities– Independent calibration of TSI monitors’ scale and degradation– Provides independent long term TSI record for climateCALCON 2002 Richard C. Willson - Columbia University 18