Open AccessTropical Pacific near‐surface currents estimated from altimeter, wind, and drifter data
Author(s) -
Lagerloef Gary S. E.,
Mitchum Gary T.,
Lukas Roger B.,
Niiler Pearn P.
Publication year - 1999
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/1999jc900197
Subject(s) - drifter , geology , geostrophic wind , equator , wind stress , climatology , ekman transport , sea surface height , ocean gyre , latitude , zonal and meridional , ekman layer , ocean current , middle latitudes , scatterometer , geostrophic current , geodesy , sea surface temperature , oceanography , upwelling , wind speed , boundary layer , physics , lagrangian , mathematical physics , subtropics , fishery , biology , thermodynamics
Tropical surface currents are estimated from satellite‐derived surface topography and wind stress using a physically based statistical model calibrated by 15 m drogue drifters. The model assumes a surface layer dominated by steady geostrophic and Ekman dynamics. Geostrophy varies smoothly from a β plane formulation at the equator to an ƒ plane formulation in midlatitude, with the transition occurring at ∼2°–3° latitude. The transition is treated with a Gaussian weight function having a meridional decay scale that is found to be approximately the Rossby radius (∼2.2° latitude). The two‐parameter Ekman model represents drifter motion relative to wind stress, with downwind flow along the equator and turning with latitude. Velocities computed from satellite data are evaluated statistically against drifter velocities and equatorial current moorings. Examples of the geostrophic and Ekman flow fields in the western Pacific during a westerly wind burst in late December 1992 depict a strong eastward flow and equatorial convergence. A comparison between December 1996 and June 1997 illustrates the basin‐wide reversal of equatorial surface flow during the onset of the 1997 El Niño.