1. ATSR Re-analysis for Climate (ARC) Chris Merchant The University of Edinburgh

2. Participants Owen Embury Stuart MacCallum Mark Filipiak Chris Old Nick Rayner Liz Kent David Llewellyn-Jones Roger Saunders Karsten Fennig Andrew Birks Tim Nightingale Martin Juckes Gary Corlett Lizzie Good Dave Berry Matt Pritchard + team

3. ARC SST goals 1.Independent record of SSTs (Aug 1991 – Dec 2009) 2.0.1 O radiometric (skin) and “drifter-depth” (bulk) SSTs 3.Biases <0.1 K, regionally 4.Target stability  0.05 K decade -1, regionally i.Discontinuities understood & removed ii.Consistency between sensors <<0.1 K 5.Comprehensive error characterization: i.Retrieval errors (random and systematic, particularly trends) ii.Methodological artefacts (channels used, cloud screening) Merchant, Llewellyn-Jones, Saunders, Rayner, Kent, et al Deriving a sea surface temperature record suitable for climate change research from the along-track scanning radiometers, Adv. Sp. Res., 41 (1), 1-11, 2008.

4. Numbers of observations Ships Drifters Moorings Graph provided by John Kennedy

5. Three elements Cloud detection Retrieval Adjustments

6. Cloud detection Will appraise improved “SADIST” and alternative “Bayesian” cloud detection Prior expectation of clear sky pixel Prior knowledge of atmospheric state BT1 BT2 PDFclear PDFcloudy X

7. Development of Bayesian approach SADIST-screened pixels PDFcloudy v2 Multi-scale OI SSTs v(-1) ECMWF NWP inc. prior SST Reprocess mission PDFcloudy v1 Reprocess mission SSTs v0 Reprocess mission PDFcloudy v3 SSTs v(-2)

8. Bayes (PDF v2) SADIST SDs of Nadir-only minus Dual-view SSTs, day-time

9. Monthly composite, Feb 2003 (A)RC screening SADIST

10. Monthly composite, Aug 2002 (A)RC screening SADIST

11. SST retrieval step Improved coefficients Not optimal estimation

12. Improved coefficients Atmospheric transmittance LBL model Time/seasonal/zonal trace gases Surface emissivity and reflection Marine aerosol with scattering Full account taken of viewing geometry Responsive to instrument noise Solar source of infra-red Saharan Dust Index Coefficients stratified by water vapour regime

13. AATSR 12 um problem Official 12 um spectral response function / calibration is wrong Solution: reference all AATSR retrievals using 12 um channel to a “dual 3.7/11” retrieval Preserves independence

14. ARC AATSR v. drifters, 2003 Median and Robust SD

17. Adjustments Skin SST to drifter-depth SST +30 min adjustment for Envisat with respect to the diurnal cycle Calibration adjustment of old to new sensors across each overlap period

18. Next steps ARC SST v0Verification work:Overlap analyses: RadiometricBT & SST Drifter Climate analyses Detection of residual trends Due end 2009 Synthesis of verification results Final adjustments (overlap, trend artefacts if required) SST v1 0.1 degree 3-day composites Spatially complete multi-scale OI 1991 – 2009 Full resolution L2P? 1991 – 2009 Short-delay or NRT mode, ongoing from 2010?

19. Comments? Planned products 0.1 o 3-day composite skin, subskin/drifter-depth Spatially complete OI, same resolution Full resolution L2P? Ongoing short-delay mode from 2010?