OSCAR

Products / Announcements / Temporal & Spatial Resolution / Documentation / Known Problems & Issues / FAQs / Citations/Ref. / Acronyms

Mission
OSCAR are the near surface currents calculated from altimetric and scatterometric satellite measurements. Quasi-linear and steady flow momentum equations are used to derive the currents.

oscar Image

5-Day Interval Surface Current
January 16, 2005
1.0 meter/sec
Credit: Earch & Space Research.

OSCAR Table

Products

	FTP / HEFT	s/w	6 months
Documentation: User Manual / Abstract / References	Comments:	Contains: depth, U (zonal velocity), V (meridional velocity)

Announcements

Temporal Resolution
Each file contains one year with a 5 day resolution.

Spatial resolution
1 degree grid from -69.5° to 69.5° latitude and 20.5° to 379.5° longitude.

Known Problems and Issues
These near-surface currents are estimated through a simplified diagnostic model of the surface circulation. Notably, local acceleration and non-linearities are not represented. As shown in [7], the present velocity field is best used for description of large scale and low frequency variations of surface flow (T>=20 days, L>=5° longitude). ESR currently provides the scientific community with an unfiltered velocity field (no post-processing), on a 1° X 1° grid with a 5 day resolution. Smoothing may have been induced only by the processing of the source data, that is ssh [2], W [4,5] and sst [6]; also some smoothing inherent to the method itself was caused by calculation of spatial gradient (for geostrophic and thermal-wind currents only). When comparing OSCAR to the drifter data, smoothing can also just be implied by the interpolation from the 1° X 1°/5-day grid to the drifter locations and times. This sort of indirect smoothing will be much removed when the new high-resolution OSCAR product is released (2008). ESR encourages researchers to make comparisons between this velocity field and in-situ observations on meso to short scales. As this surface current estimation is a work in progress, we are interested in any result involving the present velocity field, and we remain available for any help and discussion.

Frequently Asked Questions

Citations/References
1. Bonjean, F., and G. S. E. Lagerloef, 2002. Diagnostic model and analysis of
the surface currents in the tropical Pacific Ocean. J. Phys. Oceanogr., vol. 32, pg. 2938-2954.
http://www.esr.org/documents/bonjean/bl2002/bl2002.pdf

2. SALP-MU-P-EA-21065-CLS, Edition 1.9, June 2008 Ssalto/Duacs User
Handbook : (M)SLA and (M)ADT Near-Real Time and Delayed Time Products (http://www.aviso.oceanobs.com/fileadmin/documents/data/tools/hdbk_duacs.pdf )
.

3. Rio, M. H. and F. Hernandez, 2004. A mean dynamic topography computed
over the world ocean from altimetry, in situ measurements, and a geoid model. J. Geophys. Res., 109, C12032, doi:10.1029/2003JC002226.

4. Atlas, R., R. Hoffman, S. Bloom, J. Jusem, and J. Ardizzone, 1996. A multi-
year global surface wind velocity dataset using SSM/I wind observations. Bull. Amer. Meteor. Soc., vol. 77, pg. 869-882.

5. Pegion, P. J., M. A. Bourassa, D. M. Legler, and J. J. O'Brien, 2000:
Objectively-derived daily "winds" from satellite scatterometer data. Mon. Wea. Rev., 128, 3150-3168.
http://www.coaps.fsu.edu/scatterometry/Qscat/gcv_glob_L2B_1x1.html )

6. Reynolds, R. W. and T. M. Smith, 1994. Improved global sea surface
temperature analyses using optimum interpolation. J. Clim., vol. 20, pg. 1576-1582. http://ingrid.ldeo.columbia.edu/SOURCES/.IGOSS/ )

7. Johnson, E. S., F. Bonjean, G. S. E. Lagerloef, and J. T. Gunn, 2007.
Validation and error analysis of OSCAR sea surface currents. J. Atm. Ocean. Tech., vol. 24, pg. 688-701.

8. http://www.esr.org/oscar_index.html

9. http://www.oscar.noaa.gov/index.html