GHRSST XI Meeting, IC-TAG Breakout Session, 22 June 2010, Lima, Peru Cross-monitoring of L4 SST fields in the SST Quality Monitor (SQUAM) GHRSST XI Science Team Meeting June 2010, Lima, Peru Alexander Ignatov 1, Prasanjit Dash 1,2, Robert Grumbine 3 1 NOAA/NESDIS, Center for Satellite Applications & Research (STAR), USA 2 Colorado State Univ, Cooperative Institute for Research in the Atmosphere (CIRA), USA 3 NOAA, National Centers for Environmental Prediction (NCEP), USA 1

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. 2

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: High-Res. Diag. Data Set : (local IC at ~250 locations) NCOF Global SST IC : 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

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 (ΔL 4 ), 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:  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

GHRSST XI Meeting, IC-TAG Breakout Session, 22 June 2010, Lima, Peru Maps of ΔL 4 Maps provide snapshot of differences, caused by different snow/ice, land/sea masks and inputs More combinations of ΔL 4 and different dates are available at L4-SQUAM webpage OISST (AVHRR based) – OSTIA, 7-June

GHRSST XI Meeting, IC-TAG Breakout Session, 22 June 2010, Lima, Peru Histograms of ΔL 4 Time series of parameters annotated on such PDFs are used for IC and consistency checks More combinations of ΔL 4 and different dates are available at L4-SQUAM webpage OISST (AVHRR based) – OSTIA, 7-June

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 7 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 dependences OISST (AVHRR based) – RTG low res. 8 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 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! 9