Surface Current Velocity OSCAR

OSCAR filtered velocity, 21 Oct 1992 — OSCAR global filtered surface velocity, 21 Oct 1992 Copyright: UHH/CEN/AJB

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Access

RESTRICTED: This link to the data set is only available for a restricted user group. The data set is only accessible in CEN/MPI net or accessible from external nets with a customer account. Please contact ICDC if you would like to access this data from outside the network.

View velocity data at LAS
Access velocity data via OPeNDAP
Data access via file system: /data/icdc/ocean/oscar_surface_current_velocity/

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Description

The subsequent data set contains global near-surface current estimates, derived using quasi-linear and steady flow momentum equations. The horizontal velocity (zonal: u- and meridional: v-components) is a vertical average over a surface layer thickness of 30 m and is directly estimated from sea surface height, near surface vector wind and sea surface temperature data as described in brief in the Users Guide, see references.

The data used were collected from various satellites and in-situ instruments. These comprise

gridded SSH anomalies (Sea Level SSH from C3S at ICDC)
an absolute SSH product based on 7 years of GRACE mission data, altimetry and hydrologic and drifter data
Near surface wind velocity (SSM/I until 07/1999, QuikSCAT (and presumably ASCAT) from 08/1999 until present
Reynolds SST at weekly temporal resolution

The model formulation used combines geostrophic, Ekman and Stommel shear dynamics, and a complementary term from the surface buoyancy gradient [Bonjean and Lagerloef, 2002, references]. More details about the method are also given on the OSCAR webpage, see references.

For both grid resolutions u- and v-components are given. For the 1 degree product additionally filtered velocities are included; see the OSCAR webpage in references for more information. For the 1/3 degree product additionally so-called "Maximum mask velocities" are included; these are basically the geostrophic component at every grid point plus any concurrent Ekman and buoyancy components. Inclusion of this latter product is driven by the different coverage of the gridded input data sets.

Last update of data set at ICDC: December 21 2023.

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Parameters

Parameters of the data set
Name	Unit	1 degree	1/3 degree
Zonal surface velocity (u-component)	m/s	x	x
Meridional surface velocity (v-component)	m/s	x	x
Filtered u-component	m/s	x	-
Filtered v-component	m/s	x	-
Maximum mask zonal surface velocity (u-component)	m/s	-	x
Maximum mask meridional surface velocity (v-component)	m/s	-	x

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Coverage, spatial and temporal resolution

Period and temporal resolution:

1992-10-05 to 2023-12-16
about 5 days (or 1/72 year)

Coverage and spatial resolution:

Global
Spatial resolution: 1 degree x 1 degree and 1/3 degree x 1/3 degree; cartesian Grid
Geographic latitude: 1 degree data: -69.5°N to 69.5°N; 1/3 degree data: -80.0°N to 80.0°N
Geographic longitude: 1degree data: 20.5°E to 379.5°E (data are shifted East by 20°); 1/3 degree data: 20.0°E to 420.0°E (data are shifted East by 20° and are repeated for another 40°)
Dimension: 1 degree data: 360 columns x 140 rows; 1/3 degree data: 1201 columns x 481 rows
Altitude: 0.0 m

Format:

NetCDF

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Data quality

The data set does not contain estimates of the uncertainty.

The authors of the data set note that the gridded data sets used to generate the OSCAR products (see description) create errors in the product due to, e.g. clouds, high wind velocity and rain in case of the near surface wind velocity and SST, residual orbit errors and long wavelength errors in case of the SSH products, and formal mapping and sampling errors.

The OSCAR product accuracy and representativity is limited by the usage of a simplified diagnostic model of the surface circulation. Effects on the near surface currents due to local acceleration and non-linearities are not taken into account. This limits the applicability of the OSCAR product to rather larger spatial scales (> 5° in longitude) and low frequency variations (> 20 days).

Information about validation and inter-comparison studies is given at the OSCAR webpage, and in various publications (see references).

The authors of the data set note that the Johnson et al. (2007) paper is a bit outdated because in the current version (2009 for the 1/3 degree data set) an updated version of the AVISO SSH anomaly is used which reduced uncertainties.

For differences in the methodology used between the 1 degree and the 1/3 degree product we refer to the Users Guide, see references.

We note that both the land mask and the sea ice mask change kind of irregularly in the two products and a not consistently used - which might prevent usage of the product too close to the coast and in certain basins.

1 degree data set:

Until Oct 26 2000: Relatively coarse landmask, some basins missing; seasonally static sea ice mask
Since Nov 1 2000: Finer resolved landmask, particularly in Caribbean and Indonesia; seasonally static sea ice mask
Since Sep 6 2014: Further refinement of landmask, now Mediterranean and Red Sea included; seasonally static sea ice mask

1/3 degree data set:

Until Oct 1 1999: Relatively coarse landmask, some basins missing, seasonally static sea ice mask; dat cut off at 60 degrees N or S
Since Oct. 6 1999: Much finer resolved landmask, but once in a while it switches back to coarser resolution; seasonal sea ice mask
Since April 7 2014: Further refinement of landmask, now Baltic Sea, Mediterranean and Red Sea included; seasonal sea ice mask
Since July 2 2015: Further small refinement of landmask, but this one is not stable over time; seasonal sea ice mask

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Contact

Kathleen Dohan
Earth & Space Research (ESR), Seattle, WA
email: kdohan (at) esr.org

John T. Gunn
Earth & Space Research (ESR), Seattle, WA
email: gunn (at) esr.org

Jessica Hausman
Physical Oceanography DAAC
email: podaac (at) podaac.jpl.nasa.gov

Stefan Kern
ICDC / CEN / University of Hamburg
email: stefan.kern (at) uni-hamburg.de

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References

Literature:

Users Guide, Ocean Surface Current Analysis (OSCAR) Third Degree Resolution User’s Handbook, 2009 (pdf, not barrier free)
Bonjean, F., and Lagerloef, G. S. E. (2002). Diagnostic Model and Analysis of the Surface Currents in the Tropical Pacific Ocean. Journal of Physical Oceanography 32, 10, 2938-2954, https://doi.org/10.1175/1520-0485(2002)032<2938:DMAAOT>2.0.CO;2
Johnson, E.S., F. Bonjean, G.S.E. Lagerloef, J.T. Gunn, and G.T. Mitchum, 2007: Validation and Error Analysis of OSCAR Sea Surface Currents. J. Atmos. Oceanic Technol., 24(4), 688–701.
Dohan, K., and N. Maximenko, 2010: Monitoring ocean currents with satellite sensors. Oceanography, 23(4), 94-103, doi:5670/oceanog.2010.08. https://doi.org/5670/oceanog.2010.08
Dohan, K., 2017, Ocean surface currents from satellite data. J. Geophys. Res. - Oceans, 122, 2647-2651, doi:10.1002/2017JC012961. https://doi.org/10.1002/2017JC012961

Websites:

OSCAR Ocean Surface Current Analyses Real-time, http://www.esr.org/research/oscar/
OSCAR Surface Currents, https://www.esr.org/research/oscar/oscar-surface-currents/

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Data citation, License, and Acknowledgments

Please cite the data as follows:

Bonjean F. and G.S.E. Lagerloef, 2002: Diagnostic model and analysis of the surface currents in the tropical Pacific ocean, J. Phys. Oceanogr., 32, 2938-2954.

and for the 1/3 degree data:

ESR. 2009. OSCAR third degree resolution ocean surface currents. Ver. 1. PO.DAAC, CA, USA. http://dx.doi.org/10.5067/OSCAR-03D01 (last access: 2023-12-19).

while for the 1 degree data use:

ESR. 2007. OSCAR 1 degree ocean surface currents. Ver. 1. PO.DAAC, CA, USA. http://dx.doi.org/10.5067/OSCAR-10D01 (last access: 2023-12-19).

and with the following acknowledgments:

Thanks to ICDC, CEN, University of Hamburg for data support.

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