Gap free SST analyses using satellite, and possibly in situ data, are the most widely used SST products for both operational and research applications. Currently more than thirty level 4 (L4) near real time and reprocessed SST analyses are publicly available from organisations and operational agencies. It is important that the SST analyses are compared and validated in order to provide information to producers to enable them to improve their analysis systems and to provide guidance to users in their particular applications.
Inter-comparison of SST analyses for climate
The IC TT inter-compared SST analyses for climate studies (analyses of at least 15 years duration) in the framework of the Copernicus Climate Change Service (C3S). The work was led by Chunxue Yang, CNR/ISMAR. The results of the study have been submitted to Journal of Climate for peer review and publication:
Yang, Chunxue, Francesca Elisa Leonelli, Salvatore Marullo, Vincenzo Artale, Helen Beggs, Bruno Bunogiorno Nardelli, Toshio Michael Chin, Vincenzo De Toma, Simon Good, Boyin Huang, Christopher J. Merchant, Toshiyuki Sakurai, Rosalia Santoleri, Jorge Vazquez-Cuervo, Huai-Min Zhang, Andrea Pisano (2020) Sea Surface Temperature intercomparison in the framework of the Copernicus Climate Change Service (C3S), J. Climate (submitted).
Preliminary results were reported to the GHRSST-XXI Science Team Meeting (view the presentation here) and a final report to the Science Team will be made at GHRSST XXII Science Team Meeting in 2021.
Understanding the differences between SST analysis systems
The number of drifting buoy observations used in an SST analysis system depends on many factors such as Quality Control, observation error, weighting relative to the background, and correlation length scale. The observation counts are system dependent even if the data received by the systems are the same. Results of a short study on the availability of drifting buoy observations in various operational SST analyses led by Xu Li (NOAA/NCEP) were presented in the Task Team session at the GHRSST-XXI Meeting (view the presentation here). The study compared four global SST analysis systems (NOAA/NCEP NSST, ECCC CMC 0.1 degree, ABoM GAMSSA and UKMO OSTIA) The numbers, total and used, of drifting buoy observations based on the 10-day daily average for 1-10 May 2020 were examined. As expected, the total number of drifting buoy observations ingested is different for each L4 product due to different quality control, data time windows, start times and cut-off times. CMC is the only L4 system to choose only one report per platform per day. GAMSSA is the only system to reject in situ data suspected of experiencing a diurnal signal.
The way in situ data are used in operational L4 systems (directly assimilated, quality control or bias correction of satellite data, etc.) is being investigated. The study will examine the impact of ingesting BUFR format ship SST data from the GTS and the impact of COVID-19 on the total number and type of in situ data ingested into operational SST analysis systems. Results will be reported to the Science Team at the GHRSST-XXII Science Team Meeting (2021).
Feature resolution in different SST analyses
An investigation examining SST gradients in SST analyses is led by Jorge Vazquez. SST gradients in L2, L3 and L4 SST products in highly variable regions are validated using SailDrone data; results are published in
Vazquez-Cuervo, J.; Gomez-Valdes, J.; Bouali, M. (2020) Comparison of Satellite-Derived Sea Surface Temperature and Sea Surface Salinity Gradients Using the SailDrone California/Baja and North Atlantic Gulf Stream Deployments. Remote Sens., 12, https://doi.org/10.3390/rs12111839.
An online visualisation tool for L4 SST gradients is being tested in the NOAA OceanView system and a visualisation tool for marine heatwaves is in development. These tools are expected to be released for public use in 2021 and will be demonstrated at GHRSST-XXII.
Marouan Bouali, Prasanjit Dash and Jorge Cuervo-Vazquez are comparing L4 ocean fronts in highly dynamic regions. Using the NOAA/NESDIS/STAR OceanView web portal (currently in development), they are using a Sobel filter with a fixed threshold to extract fronts of interest and their characteristics i.e. mean gradient and length.
Last report to the Science Team (GHRSST-XXI, 2020)
Beggs, Helen, Chunxue Yang, Vincenzo Artale, Bruno Buongiorno Nardelli, Vincenzo De Toma, Francesca Elisa Leonelli, Salvatore Marullo, Andrea Pisano, Rosalia Santoleri, Xu Li, Boyin Huang, Prasanjit Dash, Jorge Vazquez, Simon Good, Chongyuan Mao and the IC Task Team (2020) SST Climatology and Analysis Inter-Comparison Task Team Report, Presented at the 21st GHRSST Science Team Meeting, Virtual Meeting hosted by EUMETSAT, 1st – 4th June 2020.
Task Team Members
Co-Chairs: Helen Beggs and Chunxue Yang
Members: Andrea Pisano, Francesca Elisa Leonelli, Bruno Buongiorno Nardelli, Rosalia Santoleri, Salvatore Marullo, Vincenzo Artale, Vincenzo De Toma, Toshio (Mike) Chin, Jorge Vazquez, Christopher Merchant, Simon Good, Chongyuan Mao, Toshiyuki Sakurai, Boyin Huang, Huai-Min Zhang, Xu Li, Dorina Surcel-Colan, Prasanjit Dash, Marouan Bouali, Owen Embury, Jon Mittaz, Alexander Ignatov, Eileen Maturi, Andy Harris, Alexey Kaplan, Charlie Barron, Chunying Liu, Gang Pan, Robert Schlegel, Xuepeng Zhao.