Global surface currents: a high-resolution product for investigating ocean dynamics

A global 1/4° resolution product of surface currents has been developed by the Centre de Topographie des Océans et de l’Hydrosphère. The surface current is calculated from a combination of Ekman currents derived from wind estimates from QuikSCAT satellite, geostrophic current anomalies derived from altimetry, and a mean geostrophic current derived from climatology. In the equatorial band, the currents are adjusted following the methodology proposed by Lagerloef et al. (J Geophys Res, 104(C10):22313–22326, 1999). These satellite-derived currents have been compared to different types of in situ current observations. A global validation is performed using Lagrangian surface drifting buoys and acoustic Doppler current profiler current observations along ship tracks. The comparison shows a very good agreement in the subtropical and mid-latitude bands. The correlation between the satellite-derived currents and the drifter currents in zonal mean bands is around 0.7 for most of the world oceans, both for the zonal and the meridional components. This correlation rises up to 0.8 in the regions of strong boundary currents. In the equatorial band, the correlation with the surface drifting buoys is reduced. A direct comparison with the TOGA/TAO moored current meter data at the equator shows that the low frequency currents are captured by the satellite current product, but there is a substantial high-frequency signal (<20 days), which is not reproduced. This is especially the case for the meridional component and is mainly related to the tropical instability waves. We also show that using daily QuikSCAT wind forcing improves the satellite current product, particularly in the high-latitude westerly wind belt and in the tropical Indian Ocean.

[1]  Michael H. Freilich,et al.  Observations of coupling between surface wind stress and sea surface temperature in the Eastern Tropical Pacific , 2001 .

[2]  El Niño Tropical Pacific Ocean surface current and temperature evolution in 2002 and outlook for early 2003 , 2003 .

[3]  Antonio J. Busalacchi,et al.  The Tropical Ocean‐Global Atmosphere observing system: A decade of progress , 1998 .

[4]  S. Rintoul,et al.  Seasonal and interannual evolution of the mixed layer in the Antarctic Zone south of Tasmania , 2004 .

[5]  L. Talley,et al.  Surface drifter exchange between the North Atlantic subtropical and subpolar gyres , 2006 .

[6]  W. White,et al.  Coupling of Extratropical Mesoscale Eddies in the Ocean to Westerly Winds in the Atmospheric Boundary Layer , 2003 .

[7]  J. Picaut,et al.  Use of the geostrophic approximation to estimate time-varying zonal currents at the Equator , 1989 .

[8]  D. Halpern,et al.  Observations of 20-Day Period Meridional Current Oscillations in the Upper Ocean along the Pacific Equator , 1988 .

[9]  H. Bryden,et al.  Observations of the Ekman Balance at 8°30′ N in the Arabian Sea during the 1995 Southwest Monsoon , 1997 .

[10]  D. Chelton,et al.  Surface Eddy Momentum Flux and Velocity Variances in the Southern Ocean from Geosat Altimetry , 1994 .

[11]  H. Seidel,et al.  Equatorial currents in the Pacific Ocean 1992–1997 , 1999 .

[12]  J. Picaut,et al.  Mechanisms of the 1997–1998 El Niño–La Niña, as inferred from space‐based observations , 2002 .

[13]  A. Weaver,et al.  Evidence of change in the sea of okhotsk: Implications for the north pacific , 2003 .

[14]  The geostrophic balance of the Pacific Equatorial Undercurrent , 1984 .

[15]  B. Subrahmanyam,et al.  Sea surface height variability in the Indian Ocean from TOPEX/POSEIDON altimetry and model simulations , 2000 .

[16]  J. Church,et al.  Ocean Circulation and Climate: Observing and Modelling the Global Ocean , 2001 .

[17]  Tropical instability wave kinematics: Observations from the Tropical Instability Wave Experiment , 1995 .

[18]  L. Prieur,et al.  A 1 year sea surface heat budget in the northeastern Atlantic basin during the POMME experiment: 1. Flux estimates , 2005 .

[19]  Elise Ralph,et al.  Wind-Driven Currents in the Tropical Pacific , 1999 .

[20]  C. Eden,et al.  Sea surface height changes in the North Atlantic Ocean related to the North Atlantic Oscillation , 2001 .

[21]  J. McWilliams,et al.  Dynamically balanced absolute sea level of the global ocean derived from near‐surface velocity observations , 2003 .

[22]  Scott C. Doney,et al.  The role of mesoscale variability on plankton dynamics in the North Atlantic , 2001 .

[23]  Simon Benhamou,et al.  Homing in green turtles Chelonia mydas: oceanic currents act as a constraint rather than as an information source , 2006 .

[24]  M. Mcphaden,et al.  Dynamics of Seasonal and Intraseasonal Variability in the Eastern Equatorial Pacific , 1988 .

[25]  Uwe Send,et al.  Observations of Deep Convection in the Gulf of Lions, Northern Mediterranean, during the Winter of 1991/92 , 1996 .

[26]  R. Morrow,et al.  Water properties and transport of the Leeuwin Current and Eddies off Western Australia , 2005 .

[27]  Gilles Reverdin,et al.  North Atlantic Ocean surface currents , 2003 .

[28]  Fangxin Fang,et al.  Anatomy of three warm-core Leeuwin Current eddies , 2003 .

[29]  D. Roemmich,et al.  A Comparison of Measured and Wind-derived Ekman Transport at 11°N in the Atlantic Ocean , 1991 .

[30]  J. Price,et al.  Stratified Ekman layers , 1999 .

[31]  Gary S. E. Lagerloef,et al.  Diagnostic Model and Analysis of the Surface Currents in the Tropical Pacific Ocean , 2002 .

[32]  Laurence C. Breaker,et al.  A Proposed Definition for Vector Correlation in Geophysics: Theory and Application , 1993 .

[33]  F. Hernandez,et al.  A mean dynamic topography computed over the world ocean from altimetry, in situ measurements, and a geoid model , 2004 .

[34]  M. Mcphaden,et al.  Seasonal variability in the surface currents of the equatorial Pacific , 1994 .

[35]  G. D. Strøm,et al.  Radar satellites: A new tool for pollution monitoring in coastal waters , 1996 .

[36]  R. Legeckis.  Long Waves in the Eastern Equatorial Pacific Ocean: A View from a Geostationary Satellite , 1977, Science.

[37]  G. Dibarboure,et al.  Velocity Mapping Capabilities of Present and Future Altimeter Missions: The Role of High-Frequency Signals , 2002 .

[38]  Gary S. E. Lagerloef,et al.  Validation and Error Analysis of OSCAR Sea Surface Currents , 2007 .

[39]  C. Provost,et al.  Mesoscale variability from a high-resolution model and from altimeter data in the North Atlantic Ocean , 2004 .

[40]  G. Mitchum,et al.  Tropical Pacific near‐surface currents estimated from altimeter, wind, and drifter data , 1999 .

[41]  P. Niiler,et al.  Temporal Variability of the Large-Scale Geostrophic Surface Velocity in the Northeast Pacific* , 1997 .

[42]  D. Olson,et al.  Surface current distributions in the tropical Indian Ocean derived from compilations of surface buoy trajectories , 1990 .

[43]  Gilles Reverdin,et al.  Global high-resolution mapping of ocean circulation from TOPEX/Poseidon and ERS-1 and -2 , 2000 .