OSCAR
Ocean Surface Current Analyses Real-time
Principal InvestigatorKathleen DohanCo-InvestigatorGary LagerloefOthersJohn Gunn |
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Overview
Ocean Surface Currents Analyses Real-time (OSCAR) is a project to calculate ocean surface velocities from satellite fields. Surface currents are provided on global grid every ~5 days, dating from 1992 to present day, with daily updates and near-real-time availability. The data is freely available through two data centers operated by NOAA and NASA. The NOAA site (www.oscar.noaa.gov) serves OSCAR currents on a 1 degree global grid. This site provides data in both downloadable images and netcdf format. Validation statistics are also provided through this site. The NASA PO.DAAC site (http://podaac.jpl.nasa.gov) serves OSCAR currents on both 1 degree and 1/3 degree grid spacing in netcdf format only.
The OSCAR product is a direct computation of global surface currents using satellite sea surface height, wind, and temperature. Currents are calculated using a quasi-steady geostrophic model together with an eddy viscosity based wind-driven ageostrophic component and a thermal wind adjustment. The model calculates a surface current averaged over the top 30m of the upper ocean.
In 2009 the OSCAR product was developed to calculate data on a 1/3 degree grid. Many smaller-scale features are now observable in the higher resolution model, for example the Gulf Stream rings in the images below. The spatial coverage of OSCAR has been extended to as close to the coast as possible, variable with time, expanding and contracting with the bounds of the satellite data. A former bias in velocity magnitude with latitude in the OSCAR 1-degree data is now removed with the improved resolution. A dynamically improved model for the equatorial region has been developed and implemented in the 1/3 degree OSCAR system.
Figure. Snapshots of OSCAR 1 degree and OSCAR 1/3 degree in the Gulf Stream region on the left for a sample day, September 01, 2007. Colors denote speed, vectors denote current magnitude and direction.
OSCAR is an ongoing research project intended to improve the calculation of surface currents from satellite data, and validation methods. At present, currents averaged over the top 30m of the ocean are provided on a 5-day timebase, with a 10-day smoothing, based on steady Ekman dynamics. The quasi-steady calculation has been proven to be successful for steady winds and on basin-wide scales. However, to capture small-scale wind-driven surface currents, unsteady dynamics must be included in the model. Future plans are to develop the wind-driven component to include local time-dependent wind dynamics, to exploit the enhanced vector winds from multiple satellites, to incorporate vertical mixing processes, and to investigate vertical processes controlling basin-wide transport. At present, a real-time version of OSCAR, with daily output, is being used to map the circulation in the Gulf of Mexico. A movie of 20 days of surface current data can be seen HERE.
Earth and Space Research continually performs extensive calibration and validation with both 15m drogued drifters (World Wide Drifter Buoy Deployment data, http://www.aoml.noaa.gov/phod/dac/gdp_doc.html) and with moorings from the TAO/TRITON and PIRATA arrays, from the PMEL Ocean Climate Station (OCS), and other sites within the global network of OceanSITES time series reference sites. Archives of validation studies are provided on the NOAA website.
OSCAR has a broad user interest. The NOAA OSCAR website received 72,897 hits in January 2010 from 3556 unique domains in 73 countries and was linked to from 951 websites. Additionally, in the same month, the OSCAR OPeNDAP interface received 8633 hits and delivered 2.4 Gigabyes of OSCAR data. OSCAR has a strong user base in the boating community. The data are also in use for fishery resource management research, marine animal migrations studies, and other maritime applications. OSCAR can also be used indirectly in determining wind stress and bulk air-sea fluxes since in air-sea flux algorithms the wind stress and heat fluxes depend upon wind relative to surface flow.
The OSCAR analyses have been used extensively in climate studies, such as for ocean heat storage and phytoplankton blooms. Monthly maps and anomalies are published every month in the Climate Diagnostic Bulletin (http://www.cpc.noaa.gov/products/CDB/), January 2001-present. They are used routinely to monitor ENSO and to test prediction models, with the surface current ENSO index typically leading the SST index by months (see www.esr.org/enso_index.html).
The Partners:
Multiple institutions and their facilities are critical to this project:The NOAA/NESDIS Laboratory for Satellite Altimetry is an established facility for operational altimeter data processing for NOAA. They will provide the timely access to the altimeter IGDR data sets, plus any necessary altimeter error correction and data processing. The end-product surface current processing and data center is located here as well.
The University of South Florida Department of Marine Science is where Gary Mitchum is a faculty professor and has been PI on the on-going NASA-funded Topex/Poseidon research through which the altimeter gridding analysis and the surface current analyses have been developed. They have extended the gridding analysis to include multiple altimeters and provide routine surface height fields.
The Florida State University (FSU), Center for Ocean and Atmosphere Prediction Studies (COAPS) has a long standing legacy of providing gridded ocean wind data to the research community using both conventional ship and satellite based data. Mark Bourassa is leading the effort for processing scatterometer winds.
Earth and Space Research (ESR) is the site where the work is on-going to develop and improve the models and algorithms for computing surface velocities, distribute data to colleagues, and provide the pilot monthly analyses to Climate Diagnostics Bulletin.
The NOAA Hawaii CoastWatch node serves a wide audience of maritime users in the Pacific. This existing NOAA facility will be key to communication, education and accessibility for the surface current data.
The Naval Research Laboratory in Mississippi has a strong program in satellite oceanography and works with the Naval Oceanographic Office to provide near-real time, global ocean analyses and forecasts based on all available altimeters.
The National Centers for Environmental Prediction (Vern Kousky) delivers national and global weather, water, climate and space weather guidance, forecasts, warnings and analyses to its Partners and External User Communities.
The NOAA/Pacific Marine Environmental Laboratory (Willa Zhu and Nancy Soreide) developed and serve the OSCAR website.
Links
The OSCAR web page is www.oscar.noaa.govPresentations
Status of Ocean Surface Current Analyses Real-time (OSCAR) and on the OSCAR-2 follow-on project (talk), F. Bonjean, G. Lagerloef, E. Johnson, J. Gunn, G. Mitchum, M. Bourassa, R. Cheney, and R. Legeckis, Ocean Surface Topography Science Team meeting, St. Petersburg, Florida, November 4-6, 2004.
Interviews
Watch video clip interviews of ESR scientists, Dr. Gary S.E. Lagerloef and Dr. Fabrice Bonjean, as part of the educational development materials for NASA sponsored website on Ocean Surface Currents of which Ocean Surface Currents Analyses Real Time (OSCAR) is a part. The interviews and the NASA website were developed by Dr. Henry David Snyder of Gallaudet University and M. Sara Tweedie of Tweedie & Associates, NASA HQ.
NASA's OCEANMOTION website, featuring the OSCAR dataset, is a public education project about ocean surface currents. It also features the interviews with ESR scientists, Fabrice Bonjean and Gary Lagerloef.