A TSI Community-Consensus Composite Greg Kopp LASP / Univ. of Colorado SIST Meeting Lanham, MD 11 May 2017 TSI Composite Greg Kopp - p. 1 Traditional TSI Composites SIST Meeting Lanham, MD 11 May 2017 TSI Composite Greg Kopp - p. 2 Issues with Traditional Composites • Created by individuals (PIs) • Binary (and biased) selection of instrument data used – Discontinuities at boundaries • Controversial corrections applied to data records • Normalizations incorrect • Lack uncertainties SIST Meeting Lanham, MD 11 May 2017 TSI Composite Greg Kopp - p. 3 Working on “Community Consensus” TSI Composite Includes efforts of former ISSI team and current SIST team SIST Meeting Lanham, MD 11 May 2017 TSI Composite Greg Kopp - p. 4 Improvements in Planned Composite • Recent improvements to absolute accuracy in the newer TSI measurements have not yet been reflected consistently in TSI composites – Picard/PREMOS, TCTE, CLARA, and TSIS help transfer improved ground-based calibrations to space • Weight data from all available instruments • Use unbiased statistically-driven approach rather than favored instrument • Include time-dependent uncertainties to indicate temporal regions where contributing data may be suspect • Smooth transitions and gaps scale-wise SIST Meeting Lanham, MD 11 May 2017 TSI Composite Greg Kopp - p. 5 ISSI Team Laid Groundwork 1. Agreed upon the absolute value to use for the composite TSI record 2. Agreed upon an unbiased computational methodology to create this new composite Team: Greg Kopp (PI), Will Ball, Steven Dewitte, Thierry Dudok de Wit, André Fehlmann, Wolfgang Finsterle, Claus Fröhlich, Sabri Mekaoui, Werner Schmutz, Richard Willson, Pia Zacharias SIST Meeting Lanham, MD 11 May 2017 TSI Composite Greg Kopp - p. 6 SIST Effort 1. Demonstrate, implement, and improve the computational methodology to create a new community-consensus TSI composite including time-dependent uncertainties with (partial) continued involvement from ISSI team 2. Distribute the composite to public and produce a publication detailing the methodology 3. Establish a system to update this TSI composite regularly as new data are available Summary: Provide data users with a single TSI composite including, for the first time, timedependent uncertainties, a non-binary selection of contributing instruments, and an unbiased weighting of those instruments SIST Meeting Lanham, MD 11 May 2017 TSI Composite Greg Kopp - p. 7 SIST Team Collaborators SIST Meeting Lanham, MD 11 May 2017 TSI Composite Greg Kopp - p. 8 New TSI-Composite Methodology Has Been Published • TSI-community based for openness • Uses all available instrument data Geophysical Research Letters • Scale-wise weightings smoothly fill gaps RESEARCH LETTER • Uses an unbiased statistical approach • Normalized to most accurate instruments • Has time-dependent uncertainties 10.1002/2016GL071866 Key Points: • We present a new approach for merging different solar irradiance time series into a single composite • We provide a new and fully traceable composite of the total solar irradiance • We quantify uncertainties in the total solar irradiance composite and demonstrate a 1∕f scaling in them Supporting Information: • Supporting Information S1 Correspondence to: T. Dudok de Wit, ddwit@cnrs-orleans.fr Citation: Dudok de Wit, T., G. Kopp, C. Fröhlich, and M. Schöll (2017), Methodology to create a new total solar irradiance record: Making a composite out of multiple data records, Geophys. Res. Lett., 44, doi:10.1002/2016GL071866. Received 7 NOV 2016 Accepted 24 JAN 2017 Accepted article online 27 JAN 2017 Methodology to create a new total solar irradiance record: Making a composite out of multiple data records Thierry Dudok de Wit1 , Greg Kopp2,3 , Claus Fröhlich4 , and Micha Schöll1,5 1 LPC2E, CNRS and University of Orléans, Orléans, France, 2 Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, Boulder, Colorado, USA, 3 Max-Planck-Institut für Sonnensystemforschung, Göttingen, Germany, 4 Dählenwaldstrasse 30, Davos Wolfgang, Switzerland, 5 Physikalisch Meteorologisches Observatorium Davos and World Radiation Center, Davos Dorf, Switzerland Abstract Many observational records critically rely on our ability to merge different (and not necessarily overlapping) observations into a single composite. We provide a novel and fully traceable approach for doing so, which relies on a multiscale maximum likelihood estimator. This approach overcomes the problem of data gaps in a natural way and uses data-driven estimates of the uncertainties. We apply it to the total solar irradiance (TSI) composite, which is currently being revised and is critical to our understanding of solar radiative forcing. While the final composite is pending decisions on what corrections to apply to the original observations, we find that the new composite is in closest agreement with the PMOD composite and the NRLTSI2 model. In addition, we evaluate long-term uncertainties in the TSI, which reveal a 1∕f scaling. 1. Introduction Combining different (and only partly overlapping) time series of the same physical quantity into a single composite is both a scientific and a statistical challenge that arises in many contexts, in particular in paleoclimatic reconstructions [Mann et al., 2008]. In space sciences, observations are often constrained by the finite lifetimes of satellites, making composites the key to investigation over long timescales. A timely and demanding application is the reconstruction of the total solar irradiance (TSI), which is the spatially and spectrally integrated radiant output from the Sun at a mean Sun-Earth distance of 1 AU [Kopp, 2014]. The TSI has been continuously measured since November 1978 by over a dozen instruments and is paramount to understanding the Earth’s global energy budget [Trenberth et al., 2009]. Weak secular variations in the TSI are hotly debated, as they may have large implications on our understanding of the role of the Sun in climate change [Ermolli et al., 2013]. SIST Meeting Lanham, MD 11 May 2017 TSI Composite The nominal value of the TSI, averaged over Solar Cycle 23 (which lasted from 1996 to 2008), is 1361.0 ± 0.5 Kopp - p. cycle 9 (W/m2 ), with a weak peak-to-peak solar cycle modulation of 0.08% that is in phase Greg with the 11 year Power Spectra Help Determine High-Frequency Uncertainties Plotted PSDs include real solar variability plus instrument instabilities & noise SIST Meeting Lanham, MD 11 May 2017 TSI Composite Greg Kopp - p. 10 Measurement Differences Show 1/f Power Scaling • Dispersion is not indicative of linear trends or of white noise • Use as noise model of each instrument for scale-dependent weightings based on highfrequency predictive-model correlations SIST Meeting Lanham, MD 11 May 2017 TSI Composite Greg Kopp - p. 11 Wedge Trends in Differences Are Misleading • Linear trends in instrument differences are not what is observed • Linearly-increasing uncertainties overestimate actual uncertainties in time (eventually) SIST Meeting Lanham, MD 11 May 2017 TSI Composite Greg Kopp - p. 12 Wavelet Analyses Determine Temporal Regions of Influence SIST Meeting Lanham, MD 11 May 2017 TSI Composite Greg Kopp - p. 13 TSI-Composite Improvements. And What Needs Improving • TSI composite improved with reduced biases and better instrument-transition overlaps – Methodology demonstrated, but final composite needs refining • Agree on amount of “early increase” correction (if any) to apply • Estimate initial uncertainties TSI instrument and composite data are available at: • Update regularly http://spot.colorado.edu/~koppg/TSI SIST Meeting Lanham, MD 11 May 2017 TSI Composite Greg Kopp - p. 14 Future Efforts • Improvements to composite itself – – – – Modify initial weightings based on known instrument artifacts Consider appropriateness of applying 1/f spectral variation to all instruments Improve method of adding/losing instruments Normalize to ISSI-team’s agreed upon absolute value method of weighting all instruments • Implement computational methodology to provide regular updates as new data or instruments become available • Publish and serve resulting composite to research community SIST Meeting Lanham, MD 11 May 2017 TSI Composite Greg Kopp - p. 15