GHRSST XI Science Team Meeting 21-25 June 2010, Lima, Peru

1. 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 Meeting21-25 June 2010, Lima, Peru Alexander Ignatov1, Prasanjit Dash1,2, Robert Grumbine3 1NOAA/NESDIS, Center for Satellite Applications & Research (STAR), USA 2Colorado State Univ, Cooperative Institute for Research in the Atmosphere (CIRA), USA 3NOAA, National Centers for Environmental Prediction (NCEP), USA 1

2. 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. 2

3. 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 3

4. 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 4

5. Maps of ΔL4 OISST (AVHRR based) – OSTIA, 7-June-2010 • 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 5

6. Histograms of ΔL4 OISST (AVHRR based) – OSTIA, 7-June-2010 • 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 6

7. Time Series Mean of “L4 – reference L4”Reference L4:RTG low res. • 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 ?) L4 SSTs – 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 • 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). 7

8. Timeseries zonal dependences OISST (AVHRR based) – RTG low res. • 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. 8

9. 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! 9