GHRSST XI Meeting, IC-TAG Breakout Session, 22 June 2010, Lima, Peru

Cross-monitoring of L4 SST fields in the SST Quality Monitor (SQUAM)

http://www.star.nesdis.noaa.gov/sod/sst/squam/L4/

GHRSST XI Science Team Meeting

21-25 June 2010, Lima, Peru

Alexander Ignatov1, Prasanjit Dash1,2, Robert Grumbine3

1NOAA/NESDIS, Center for Satellite Applications & Research (STAR), USA2Colorado State Univ, Cooperative Institute for Research in the Atmosphere (CIRA), USA

3NOAA, National Centers for Environmental Prediction (NCEP), USA

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GHRSST XI Meeting, IC-TAG Breakout Session, 22 June 2010, Lima, Peru

Motivation for L4 cross-monitoring in SQUAM

The SST Quality Monitor (SQUAM) was “initially” designed to monitor L2 satellite SSTs for stability and consistency (cross-platform & cross-product), in NRT, by comparing them against several L4 SSTs. The L2 SSTs include GAC and FRAC SSTs from AVHRRs onboard multiple platforms :

NESDIS heritage Main Unit Task (MUT, 2001-pr)

NESDIS Advanced Clear-Sky Processor for Oceans (ACSPO, 2008-pr)

NAVOCEANO (2000-pr)

O&SI SAF MetOp-2 FRAC (2009-pr)

Comparison of L2 SSTs against “several” L4 SSTs, however, demonstrated significant differences between the L4 products themselves, which motivated to develop a dedicated L4-SQUAM.

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GHRSST XI Meeting, IC-TAG Breakout Session, 22 June 2010, Lima, Peru

Intended users of L4-SQUAM

L4-SQUAM complements other existing intercomparison (IC) systems and efforts (the list below is not exhaustive) :

GHRSST IC-TAG: http://www.ghrsst.org/The-Inter-Calibration-TAG-(IC-TAG).html

High-Res. Diag. Data Set : http://www.hrdds.net/ (local IC at ~250 locations)

NCOF Global SST IC : http://ghrsst-pp.metoffice.com/pages/latest_analysis/sst_monitor/daily/ens

L4-SQUAM is intended to provide quick diagnostics to the developers of L4 products, as well as the user community, to choose a suitable product.

Currently, L4-SQUAM includes “SIX” daily products:

Two daily 0.25º x 0.25º (lat/lon grid) OISST (aka Reynolds)

Two daily RTG (0.5º low resolution and 1/12º high resolution)

UKMO 0.05º OSTIA, and IFREMER 0.1º ODYSSEA

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GHRSST XI Meeting, IC-TAG Breakout Session, 22 June 2010, Lima, Peru

Method of L4 intercomparison in SQUAM

The IC is made on a global scale with modules to highlight zonal differences, by analyzing differences between daily L4 products (ΔL4), which are matched in space by using nearest neighbor interpolation.

The diagnostics are made available (with one day lag) at an interactive user-friendly web interface: http://www.star.nesdis.noaa.gov/sod/sst/squam/L4/

Tabs for L4 IC in SQUAM:

Maps

Histograms

Statistical time series (# of matches, minimum and maximum, mean, median, standard deviation, robust standard deviation, skewness, kurtosis, extreme values)

Hovmöller time series of zonal differences

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GHRSST XI Meeting, IC-TAG Breakout Session, 22 June 2010, Lima, Peru

Maps of ΔL4

• Maps provide snapshot of differences, caused by different snow/ice, land/sea masks and inputs• More combinations of ΔL4 and different dates are available at L4-SQUAM webpage

OISST (AVHRR based) – OSTIA, 7-June-2010

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GHRSST XI Meeting, IC-TAG Breakout Session, 22 June 2010, Lima, Peru

Histograms of ΔL4

• Time series of parameters annotated on such PDFs are used for IC and consistency checks• More combinations of ΔL4 and different dates are available at L4-SQUAM webpage

OISST (AVHRR based) – OSTIA, 7-June-2010

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GHRSST XI Meeting, IC-TAG Breakout Session, 22 June 2010, Lima, Peru

Time Series Mean of “L4 – reference L4”Reference L4: RTG low res.

DOI_AV: OISST (AVHRR based) DOI_AA: OISST (AVHRR, AMSR-E), RTG_HR: RTG high resolution OSTIA: UK Met office ODYSSEA: IFREMER

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L4 SSTs – RTG low res.

• Time series of other statistical parameters (Std Dev, Skewness etc.) and wrt other L4 SSTs are available at the L4-SQUAM webpage.

• Additionally, interactive plots are also available which allow users to see the numerical values and focus on specific temporal coverage and L4 SSTs of particular interest (see L4-SQUAM web).

Observations:

• OISSTs track each other (some differences)

• Cold bias in OSTIA in the beginning (2006)

• Anomalous RTG high res. SST for a few days in end of Feb 2010

• Seasonal differences between L4 SSTs show cyclic patterns

• ODYSSEA generally followed OSTIA with anomalies in Apr-2008 (stopped since end of 2009 ?)

GHRSST XI Meeting, IC-TAG Breakout Session, 22 June 2010, Lima, Peru

Timeseries zonal dependencesOISST (AVHRR based) – RTG low res.

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Observations:

• Seasonal differences in northern hemisphere high latitudes (OISST warmer)

• Seasonal differences in northern hemisphere mid-latitudes (OISST colder)

• Seasonal differences in northern hemisphere low latitudes (OISST colder); mutual consistency improved since 2007.

• Also, minor differences are observed in other latitudes.

• The differences are likely due to different treatment of land/sea/ice masks.

More combinations are available at L4-SQUAM web.

GHRSST XI Meeting, IC-TAG Breakout Session, 22 June 2010, Lima, Peru

Summary and Future Work

L4-SQUAM currently monitors six daily L4 SSTs:

Two daily 0.25º x 0.25º (lat/lon grid) OISST products Two daily RTG products (0.5º low resolution and 1/12º high resolution)

UKMO 0.05º OSTIA, and IFREMER 0.1º ODYSSEA products

In general, OISSTs are mutually consistent.

Also, RTG products are somewhat mutually consistent (to a lesser degree) and require further reconciliation. (Note that, the RTG low resolution is an OISST like product whereas RTG high resolution is based on a newer physical algorithm).

OSTIA and ODYSSEA SSTs show mutual consistency, however, ODYSSEA product has been somewhat unstable (stopped production ?).

General high latitude differences between various products are likely due to different treatment of land/sea/ice mask and should be reconciled by the developers of these products.

Future plans Add GHRSST GMPE & NAVO K10 to L4-SQUAM

Work with L4 producers to reconcile different L4 SSTs

THANK YOU!

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