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MotivationMotivation SST analysis products at NCDCSST analysis products at NCDC

Extended Reconstruction SST (ERSST) v.3bExtended Reconstruction SST (ERSST) v.3b Daily Optimum Interpolation SST (OISST) v.2Daily Optimum Interpolation SST (OISST) v.2

Error computationsError computations Use of SST for Operational Climate activitiesUse of SST for Operational Climate activities

Warming trendWarming trend El NinoEl Nino Modelling (not this talk)Modelling (not this talk)

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What are operational uses of SST for climate What are operational uses of SST for climate applications?applications?

What are the uses of SST ?What are the uses of SST ?

Are SST error fields used in their operations?Are SST error fields used in their operations?

Why is there minimal use?Why is there minimal use?

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Provides historical context for Provides historical context for modern measurementsmodern measurements

Produced monthly on 2Produced monthly on 2°° grid from grid from 1854 to present1854 to present

Input: in situ data only Input: in situ data only

NetCDF 3 Gridded ProductsNetCDF 3 Gridded Productso Full SSTFull SSTo SST anomaly (wrt1971-2000 climatology)SST anomaly (wrt1971-2000 climatology)o Total error varianceTotal error variance

http://www.ncdc.noaa.gov/oa/climate/research/sst/ersstv3.php

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Daily, 1/4Daily, 1/4°° grid grid

Based on satellite and in situ dataBased on satellite and in situ datao AVHRR-only (from 1981)AVHRR-only (from 1981)o AVHRR+AMSR (from 2002)AVHRR+AMSR (from 2002)

3 Gridded Products3 Gridded Productso Full SSTFull SSTo Random and sampling error Random and sampling error

variancevarianceo Bias error varianceBias error variance

. 01 . 02 .03 .04 .05 . 06 .07

1 2 3 4 5 6 7 X 10 -3

OISST with AVHRR 17 & 18 May 15, 2010

Bias error

Random and sampling error

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Source ERSST OISST

Random •Small due to filtering and smoothing

•Lumped with sampling

Sampling •Low (decadal) frequency wrt model output•High frequency wrt detrended OI

•Expected OI increment variance reduced by observations used

Bias •Methodology changes (e.g., bucket types, engine intake)•Ship adjusted to buoys from 1970’s

•Depends on expected variance for each mode, and which modes are used for bias correction per satellite dataset

Error estimation requires a reference or expected value.Analysis steps defined how error is computed.

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AMSR reduces sampling error but not biasAMSR reduces sampling error but not bias

AV

HR

R+

AM

SR

AV

HR

R-o

nly

1 2 3 4 5 6 7 X 10 -3 .01 . 02 .03 .04 .05 . 06 .07

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After 1940s, the average trend is ~0.1°C/decadeAfter 1940s, the average trend is ~0.1°C/decade Global errors must be < 0.5°C/100 yrs or 0.05°C/10 yrsGlobal errors must be < 0.5°C/100 yrs or 0.05°C/10 yrs Regional error requirements can differRegional error requirements can differ

1941)

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Monthly ERSST

Daily OISST (AVHRR-only)

Daily OISST (AVHRR&AMSR)

Remote Sensing & Applications Division

Climate Services Division:

Climate Monitoring Branch

Monthly State of the Climate Assessment

Yearly State of the Climate Report

NCEP

NCDC

Seasonal Ocean Forecast

Global Data Assimilation System

Weekly OISST (AVHRR-only)

Climate Prediction Center

El Nino Monthly Discussion

MergedLandOcean Temperature

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SST is merged with Land temperatures for global map.Gridpoints with high error are masked out.

Emphasis on departure from normal

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Values with high Values with high errors excluded errors excluded from averages from averages

• With global With global warming, warming, all all recent years are recent years are above normalabove normal

• Thus, emphasis Thus, emphasis onon rankings rankings

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““Tie” reflects Tie” reflects rounding off rounding off NOT NOT significance significance testingtesting

Errors could Errors could also be used to also be used to define 95% CIdefine 95% CI

http://www.ncdc.noaa.gov/sotc/?report=global

Allow comparison among months and between years, rather Allow comparison among months and between years, rather than wrt normalthan wrt normal

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Fig. 2.3. 95% confidence range of decadal average temperatures for the HadCRUT3 temperature analysis (see Brohan et al. 2006 for the error model derivation).

95% CI shown by MetOffice, while also showing departure from normal

Global warming skepticism needs to be addressed

Most recent 3 decades progressively warmer

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Emphasis on use of Emphasis on use of multiple indicatorsmultiple indicators and and ensembleensemble presentationspresentations

Avoids problem of Avoids problem of deciding whether deciding whether error estimates are error estimates are equivalentequivalent

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http://www.cpc.noaa.gov/products/

Index=Sum of SST anomalies in specific region

Among teleconnection phenomena, El Nino is the only one with an SST-based index

CPC uses weekly OISST for diagnostics and forecast; ERSST for historical context

Concern: public confused why 2 SST products?

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http://www.cpc.noaa.gov/products/

Daily OISST

Monthly ERSST

• SST products will not be SST products will not be exactly the sameexactly the same

• 95% CI indicates OISST 95% CI indicates OISST is better for forecasting is better for forecasting

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NCDC SST analysis products are distributed NCDC SST analysis products are distributed with error fieldswith error fields

For operational climate assessments, errors For operational climate assessments, errors not used routinely not used routinely Error fields used only when producer is involvedError fields used only when producer is involved Users need time and resources to evaluate and Users need time and resources to evaluate and

incorporate into routine operationsincorporate into routine operations Effective communication to public a major issueEffective communication to public a major issue

Producers need to give recommendations Producers need to give recommendations and help develop protocolsand help develop protocols

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WMO has WMO has requested requested presentation be presentation be changed to terciles changed to terciles (above, below and (above, below and normal) to relate normal) to relate more easily to more easily to forecastsforecasts

But what is But what is normal? normal?

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RANDOM ERROR: caused RANDOM ERROR: caused by natural variations when by natural variations when measurement is repeatedmeasurement is repeated

SAMPLING ERROR: if SST SAMPLING ERROR: if SST estimate affected by estimate affected by distribution and densitydistribution and density

BIAS error: if SST obs BIAS error: if SST obs offset from true value by offset from true value by measurement method or measurement method or analysisanalysis

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Sampling and Random errorSampling and Random error Equal to OI analysis increment SD if there are no obsEqual to OI analysis increment SD if there are no obs Reduced proportionally by (OI wt*source error)Reduced proportionally by (OI wt*source error) SNR ratio= 1.94 ship; 0.5 buoy&AVHRR; 0.35 AMSRSNR ratio= 1.94 ship; 0.5 buoy&AVHRR; 0.35 AMSR

Bias error (systematic to measurement Bias error (systematic to measurement methodology or analysis method)methodology or analysis method) Depends on number of EOT modes used, and number of Depends on number of EOT modes used, and number of

data sourcesdata sources

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RandomRandom Assumed very small due to smoothingAssumed very small due to smoothing

SamplingSampling LF : based on annual sampling over 5X5 grid; damping ; LF : based on annual sampling over 5X5 grid; damping ;

truth=low-pass filtereds CGCM SST anomalies 1861-2000truth=low-pass filtereds CGCM SST anomalies 1861-2000 HF: mode variance and how many modes resolved; truth= HF: mode variance and how many modes resolved; truth=

detrended variance of OI anomalies v2 (1982-2005)detrended variance of OI anomalies v2 (1982-2005) BiasBias

Pre-1940: night air temp comparisonPre-1940: night air temp comparison assumed to be constant after 1940assumed to be constant after 1940

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1980s: warmest decade (at the time). Every year of 1990s warmer than 1980s average.

Every year of 2000s warmer than 1990s average.

1990s: warmest decade (at the time).