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HadISST2: progress and plans

HadISST2: progress and plans. Nick Rayner, 14 th March 2007. Aim of the presentation. To present our ideal HadISST2 in the context of recent progress To quantify the resources required for this ideal and the resources that we have

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HadISST2: progress and plans

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  1. HadISST2: progress and plans Nick Rayner, 14th March 2007

  2. Aim of the presentation • To present our ideal HadISST2 in the context of recent progress • To quantify the resources required for this ideal and the resources that we have • To ask for your input in helping to prioritise the improvements we make

  3. HadISST1 (Rayner et al, 2003) • Monthly globally complete fields of SST and sea ice concentration on a 1°x1° grid from 1871 • SST anomalies reconstructed using a two-stage reduced-space OI procedure, followed by superposition of quality-improved gridded observations. • Sea ice fields made more homogeneous by compensating passive microwave-based concentrations for surface melt effects and for algorithm deficiencies in the Antarctic and by making the historical in situ concentrations consistent with the satellite data. • SSTs near sea ice estimated using statistical relationships between SST and sea ice concentration. Data are available from http://www.hadobs.org

  4. Ideal HadISST2 • Flexible spatial and temporal resolution • Homogeneous, i.e. fully bias corrected SST and sea ice • Fully quantified uncertainties • Meaningful information everywhere • Updated both in near real time and as improved delayed mode information comes in • Fully integrated with other Met Office activities, e.g. OSTIA

  5. Ideal HadISST2 • Flexible spatial and temporal resolution • Homogeneous, i.e. fully bias corrected SST and sea ice • Fully quantified uncertainties • Meaningful information everywhere • Updated both in near real time and as improved delayed mode information comes in • Fully integrated with other Met Office activities, e.g. OSTIA

  6. Flexible spatial and temporal resolution • Different user communities require different spatial and temporal resolutions • need a flexible analysis system • HadSST2 is produced by such a flexible system (Rayner et al, 2006) 3.75°x2.5° 5°x5° 1°x1° 0.5°x0.5°

  7. Flexible spatial and temporal resolution • We have begun to develop a flexible system to apply Reduced Space Optimum Interpolation (RSOI), as used in HadISST1 (Rayner et al, 2003) • There are limits as to how fine a resolution the data will support, which will vary in time and space • With the extra data available since HadISST1 and using RSOS we suggest that a 5-day analysis is feasible back to the late 1940s. • The best-case spatial resolution will be higher than in HadISST1, but tests are needed to determine it

  8. Diurnal temperature range Hourly drifting buoy observations binned by local time, gridded, then fitted to empirical function Kennedy, Brohan and Tett (2007)

  9. Ideal HadISST2 • Flexible spatial and temporal resolution • Homogeneous, i.e. fully bias corrected SST and sea ice • Fully quantified uncertainties • Meaningful information everywhere • Updated both in near real time and as improved delayed mode information comes in • Fully integrated with other Met Office activities, e.g. OSTIA

  10. Homogeneous and fully bias corrected SST • HadSST2 includes updated “bucket” corrections through 1941 • Evidence for requirement for some post-1941 bucket corrections • Modern data mix requires application of corrections between ships, buoys and satellite data sources (Pathfinder AVHRR and (A)ATSR).

  11. Relative biases in modern SST data Ships – ATSR2 Drifters – ATSR2

  12. Ideal HadISST2 • Flexible spatial and temporal resolution • Homogeneous, i.e. fully bias corrected SST and sea ice • Fully quantified uncertainties • Meaningful information everywhere • Updated both in near real time and as improved delayed mode information comes in • Fully integrated with other Met Office activities, e.g. OSTIA

  13. Fully quantified SST uncertainties • Rayner et al (2006) quantified uncertainties due to sampling and measurement error and due to bucket corrections through 1941 • Calculate uncertainties on new bias corrections • Calculate uncertainties on underlying climatology • Comprehensive uncertainty estimates should allow us to generate multiple realisations of HadISST2

  14. Relative contributions of sampling/measurement and bias correction uncertainties Sampling/measurement (°C) Bias correction (°C) Sept 1938 Combined (°C) Ratio bias:samp

  15. Homogeneous and fully bias corrected sea ice • Revisit work of Rayner et al (2003) for HadISST1 • A reanalysis of the SMMR-SSM/I period is underway in collaboration with EUMETSAT OSISAF and NSIDC. This will feed directly into HadISST2. • Summer melt bias should be re-addressed. • Prior to satellite era, sea ice charts are used to define the concentration fields. Bias corrections between these and satellite data to be defined.

  16. Quantify uncertainties in sea ice record • SMMR-SSM/I reanalysis project includes calculation of uncertainties in retrievals due to atmospheric and surface emissivity effects • There is hope for a funding opportunity in the U.S. to start to look at the uncertainties in the sea ice chart data • New bias corrections between passive microwave and charts will have uncertainties

  17. Ideal HadISST2 • Flexible spatial and temporal resolution • Homogeneous, i.e. fully bias corrected SST and sea ice • Fully quantified uncertainties • Meaningful information everywhere • Updated both in near real time and as improved delayed mode information comes in • Fully integrated with other Met Office activities, e.g. OSTIA

  18. Meaningful information everywhere • Improve reconstruction of Southern Ocean prior to 1982 • Improve specification of near ice SST • Some periods currently have sea ice climatology in the Arctic in HadISST1, these will be replaced by data from GDSIDB and the ACSYS chart collection • Try again to identify sources of sea ice data for the Antarctic prior to 1973 and/or seek alternative solutions. • Improve lakes and inland seas

  19. Ideal HadISST2 • Flexible spatial and temporal resolution • Homogeneous, i.e. fully bias corrected SST and sea ice • Fully quantified uncertainties • Meaningful information everywhere • Updated both in near real time and as improved delayed mode information comes in • Fully integrated with other Met Office activities, e.g. OSTIA

  20. Updated both in near real time and as improved information comes in • Update data must be carefully sourced • Plan to make new releases as data are digitised or QCed in delayed mode • In both cases, bias corrections must be developed prior to ingestion

  21. Ideal HadISST2 • Flexible spatial and temporal resolution • Homogeneous, i.e. fully bias corrected SST and sea ice • Fully quantified uncertainties • Meaningful information everywhere • Updated both in near real time and as improved delayed mode information comes in • Fully integrated with other Met Office activities, e.g. OSTIA

  22. Fully integrated with other Met Office activities • Operational Sea Surface Temperature and Sea Ice Analysis (OSTIA) • Global, real-time, high-resolution SST and sea ice analysis system • Uses satellite data provided by the GHRSST project, together with in situ observations. • Analysis uses a variant of optimal interpolation (OI) • Analysis is produced daily at a resolution of 1/20° (approx. 5km).

  23. OSTIA analysis for 6th March 2007

  24. Fully integrated with other Met Office activities • We plan to: • Use common input data streams • Share QC systems • Preserve different analysis methodologies

  25. Resources • Our ideal HadISST2 requires of the order 7 person years’ effort, excluding any ongoing updating. • We plan to release HadISST2 in 2010/11. • We currently have 4 person years’ effort allocated to the work, but there may be opportunities for more. • We must prioritise to ensure delivery.

  26. Summary • We aim to produce HadISST2 by 2010/11 • Based on new understanding of the data, we can look forward to the following improvements relative to HadISST1: • Flexible spatial and temporal resolution • Homogeneous, i.e. fully bias corrected SST and sea ice • Fully quantified uncertainties • Meaningful information everywhere • Updated both in near real time and as improved delayed mode information comes in • Fully integrated with other Met Office activities, e.g. OSTIA

  27. References • Rayner, N.A. et al, 2003: Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century, Journal of Geophysical Research, Vol. 108, No. D14, 4407, doi:10.1029/2002JD002670 • Rayner, N.A. et al, 2006: Improved analysis of changes and uncertainties in sea surface temperature measured in situ since the mid-nineteenth century: the HadSST2 data set, J. Climate, 19, 446-469. • Kennedy, Brohan and Tett, 2007: A global climatology of the diurnal variations in sea-surface temperature and implications for MSU temperature trends, Geophys. Res. Lett., Vol. 34, L05712, doi:10.1029/2006GL028920

  28. Questions & Answers

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