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HadISST2: progress and plans

Nick Rayner, 14th March 2007

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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

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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

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Ideal HadISST2

Flexible spatial and temporal resolutionHomogeneous, i.e. fully bias corrected SST and sea ice

Fully quantified uncertaintiesMeaningful information everywhereUpdated both in near real time and as improved delayed mode information comes in

Fully integrated with other Met Office activities, e.g. OSTIA

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Ideal HadISST2

Flexible spatial and temporal resolutionHomogeneous, i.e. fully bias corrected SST and sea ice

Fully quantified uncertaintiesMeaningful information everywhereUpdated both in near real time and as improved delayed mode information comes in

Fully integrated with other Met Office activities, e.g. OSTIA

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Flexible spatial and temporal resolution

Different user communities require different spatial and temporal resolutionsneed a flexible analysis system

HadSST2 is produced by such a flexible system (Rayner et al, 2006)

5°x5°

1°x1°

3.75°x2.5°

0.5°x0.5°

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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 spaceWith 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

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Diurnal temperature range

Hourly drifting buoy observations binned by local time, gridded, then fitted to empirical function

Kennedy, Brohan and Tett (2007)

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Ideal HadISST2

Flexible spatial and temporal resolutionHomogeneous, i.e. fully bias corrected SST and sea ice

Fully quantified uncertaintiesMeaningful information everywhereUpdated both in near real time and as improved delayed mode information comes in

Fully integrated with other Met Office activities, e.g. OSTIA

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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).

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Relative biases in modern SST data

Ships – ATSR2

Drifters – ATSR2

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Ideal HadISST2

Flexible spatial and temporal resolutionHomogeneous, i.e. fully bias corrected SST and sea ice

Fully quantified uncertaintiesMeaningful information everywhereUpdated both in near real time and as improved delayed mode information comes in

Fully integrated with other Met Office activities, e.g. OSTIA

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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

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Relative contributions of sampling/measurement and bias correction uncertainties

Sampling/measurement (°C) Bias correction (°C)

Combined (°C) Ratio bias:sampSept 1938

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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.

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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

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Ideal HadISST2

Flexible spatial and temporal resolutionHomogeneous, i.e. fully bias corrected SST and sea ice

Fully quantified uncertaintiesMeaningful information everywhereUpdated both in near real time and as improved delayed mode information comes in

Fully integrated with other Met Office activities, e.g. OSTIA

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Meaningful information everywhere

Improve reconstruction of Southern Ocean prior to 1982

Improve specification of near ice SSTSome 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

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Ideal HadISST2

Flexible spatial and temporal resolutionHomogeneous, i.e. fully bias corrected SST and sea ice

Fully quantified uncertaintiesMeaningful information everywhereUpdated both in near real time and as improved delayed mode information comes in

Fully integrated with other Met Office activities, e.g. OSTIA

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Updated both in near real time and as improved information comes in

Update data must be carefully sourcedPlan to make new releases as data are digitised or QCed in delayed mode

In both cases, bias corrections must be developed prior to ingestion

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Ideal HadISST2

Flexible spatial and temporal resolutionHomogeneous, i.e. fully bias corrected SST and sea ice

Fully quantified uncertaintiesMeaningful information everywhereUpdated both in near real time and as improved delayed mode information comes in

Fully integrated with other Met Office activities, e.g. OSTIA

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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).

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OSTIA analysis for 6th March 2007

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Fully integrated with other Met Office activities

We plan to:Use common input data streamsShare QC systemsPreserve different analysis methodologies

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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.

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Summary

We aim to produce HadISST2 by 2010/11Based 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

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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

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Questions & Answers