ESR, in cooperation with other researchers, has been developing and improving
methodologies to compute and display tropical surface currents since 1996. This
analysis is based on geostrophic, Stommel/Ekman and thermal wind dynamics, using
satellite-based, altimeter derived sea level data, scatterometer derived wind
data, and SST data.
The above graphic links provide access to displays of the calculated surface
current throughout the global tropical ocean. The original diagnostic model
dealt with the Tropical Pacific and eventually matured into the product and
services available on the OSCAR web site (www.oscar.noaa.gov)
described in further detail below. This model has been extended, as a part of
continuing research at ESR, into the other ocean basins, as shown in the above
links. Future efforts will extend this analysis to higher latitude regions.
The present implementation of this diagnostic model of the surface circulation
in the tropical Pacific is presented on the NOPP project website "Ocean
Surface Current Analysis-Real-time". OSCAR is a pilot
processing system and data center delivering tropical Pacific Ocean surface velocity
fields via the Internet (www.oscar.noaa.gov).
Surface currents are computed from satellite altimeter and vector wind data using
methods developed during the Topex/Poseidon altimeter research mission. OSCAR
is a transition to operational oceanographic applications using Jason-1 altimeter
data. The various uses (actual or potential) include large scale climate diagnostics
and prediction, oceanographic education and research, fisheries management, monitoring
debris drift, larvae drift, oil spills, fronts and eddies, search and rescue,
naval and maritime operations, and idle curiosity. OSCAR provides velocity maps
updated on a 1-week basis within 10 days of Jason altimeter measurements. This
is made possible by (1) the rapid availability of Jason-1 Interim Geophysical
Data Records (IGDRs) within 2-3 days delay from the time of satellite measurement,
and (2) the fact that Jason-1 IGDR data approach the accuracy of scientific Topex/Poseidon
and Jason-1 altimeter Geophysical Data Records (GDRs) which are generally delayed
1-2 months. The velocity fields are published in the monthly NOAA Climate Diagnostics
Bulletin and are particularly useful in monitoring the recent evolution of ENSO
The methodology for computing surface currents is described in Bonjean and Lagerloef
(2002). Briefly, the model formulation combines geostrophic, Ekman and Stommel
shear dynamics, and a complementary term from the surface buoyancy gradient.
The field compares well with velocity observations from 15-m depth buoy drifters
and equatorial Tropical Ocean-Atmosphere mooring data. Geostrophic velocities
are computed with sea level gradients derived from sea surface height analysis
of TOPEX/Poseidon (1992-2002) and Jason (2002-present) (Lagerloef, Mitchum,
Lukas and Niiler, 1999). Surface wind pseudostresses are obtained from satellite
scatterometers (SSM/I (1992-2000) and QuikSCAT (2000-present)). A 7-year mean
surface height field was subtracted and replaced by a mean dynamic topography
derived from altimetry, in-situ measurements and the CHAMP geoid model
(Rio and Hernandez, 2004, JGR, 109).
The OSCAR web server allows user-selected geographic regions, display resolution
and scaling of image display maps, as well as access to the entire Topex/Poseidon/Jason-derived
field from 1993-present.
The OSCAR website (http://www.oscar.noaa.gov/)
allows downloading of surface velocity data in NetCDF format, or through the
OpenDAP/DODS network. The original source of the NetCDF data package is:
This work is a product of the Topex/Poseidon/Jason altimeters and the NSCAT/SeaWinds
mission science team studies involving collaborations with G. Mitchum (USF), A.
Busalacchi (NASA/GSFC), R.Lukas(U.H.), T. Liu (JPL), and P. Niiler (SIO). Gary
Lagerloef (email@example.com ) and
Fabrice Bonjean (firstname.lastname@example.org)
direct the ESR activities of these projects. John Gunn (email@example.com)
assists with the model implementation and data processing, and Susan Howard (firstname.lastname@example.org)
manages the web site.
But a PC interface edition is maintained at:
Alternatively, there is an archived version of similar software at:
Although we prefer you access data through the OSCAR web page, qualified researchers
with unique research needs may discuss specific research data sets via email
to John Gunn at
The official OSCAR web site is: www.oscar.noaa.gov
The most recent EOF map of the surface velocity and SST anomalies can be found
for the Pacific Ocean here.
Lagerloef, G.S.E., R. Lukas, F. Bonjean, J.T. Gunn, G.T. Mitchum, M. Bourassa,
A.J. Busalacchi, 2003: El Nino Tropical Pacific Ocean surface current and temperature
evolution in 2002 and outlook for early 2003, Geophys. Res. Lett., Vol. 30, No.
10, 1514, doi:10.1029/2003GL017096, 2003.
Bonjean, Fabrice, Gary S. E. Lagerloef, 2002: Diagnostic Model and Analysis of
the Surface Currents in the Tropical Pacific Ocean. J. Physical Oceano. Vol. 32,
No. 10, pp. 2938-2954.
Lagerloef,G.S.E., G.Mitchum, R.Lukas and P.Niiler, 1999: Tropical Pacific near-surface
currents estimated from altimeter, wind and drifter data, J. Geophys. Res., 104,
Ocean Surface Current Analysis - Real time, (poster) Jason/Topex/Poseidon
Science Working Team Meeting, October 2002, New Orleans, LA.
Tropical Ocean Currents Inferred From Satellite, (poster) "En Route to GODAE"
International Symposium, June 2002, Biarritz, France.
Seasonal to Interannual Variations of the Surface Currents in the Equatorial Oceans,
(Oral presentation) Ocean Sciences 2002, Honolulu, Hawaii.
Seasonal to Interannual Variations of the Surface Currents in the Tropical Atlantic
Ocean during 1993-2000, (Oral presentation) U.S. CLIVAR Atlantic Conference 12-14
June 2001, Boulder, CO.