Editorial Type:
Article
Article Type:
Research Article

Eddies Observed by Argo Floats. Part I: Eddy Transport in the Upper 1000 dbar

Katsuro Katsumata Research and Development Center for Global Change, Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan

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Print Publication:
01 Nov 2016
DOI:
https://doi.org/10.1175/JPO-D-16-0150.1
Page(s):
3471–3486
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Abstract

Argo floats measure horizontal current velocities at the parking depth and vertical profiles of temperature and salinity. The data are sufficient for simultaneous estimates of velocities and vertical displacements of isopycnal surfaces. More than 980 000 pairs of observations of current velocity and water column stratification were used to calculate eddy transport above 1000 dbar and its uncertainty based on the temporal-residual-mean framework. Eddy transports larger than 1.0 m2 s−1 were found in the North Atlantic, western North Pacific, and Southern Oceans. The eddy transport T had components perpendicular and parallel to the density contours at 1000 dbar. In the midlatitude oceans, eddy transport was weaker (<0.5 m2 s−1), mostly perpendicular to the density contours, and equatorward. A large area of northward was found in the south Indian Ocean; analysis of velocity and thickness perturbations suggested that this transport was a northward intrusion of Antarctic Intermediate Water. In the midlatitude oceans and in most of the southern part of the Antarctic Circumpolar Current (ACC), was generally upgradient in density on 1000 dbar. Downgradient was found along the North Atlantic Current and Kuroshio Extension as well as in the northern part of the ACC. Zonally integrated meridional transport was poleward at latitudes higher than approximately 40° and equatorward at lower latitudes. The quasi-Stokes or Gent–McWilliams diffusivity coefficient was on the order of 1000 m2 s−1 but was associated with such large uncertainty that it was statistically indistinguishable from zero, except at midlatitudes in the Southern Hemisphere.

Corresponding author address: Katsuro Katsumata, RCGC, JAMSTEC, 2-15 Natsushima, Yokosuka, Japan. E-mail: k.katsumata@jamstec.go.jp

Abstract

Argo floats measure horizontal current velocities at the parking depth and vertical profiles of temperature and salinity. The data are sufficient for simultaneous estimates of velocities and vertical displacements of isopycnal surfaces. More than 980 000 pairs of observations of current velocity and water column stratification were used to calculate eddy transport above 1000 dbar and its uncertainty based on the temporal-residual-mean framework. Eddy transports larger than 1.0 m2 s−1 were found in the North Atlantic, western North Pacific, and Southern Oceans. The eddy transport T had components perpendicular and parallel to the density contours at 1000 dbar. In the midlatitude oceans, eddy transport was weaker (<0.5 m2 s−1), mostly perpendicular to the density contours, and equatorward. A large area of northward was found in the south Indian Ocean; analysis of velocity and thickness perturbations suggested that this transport was a northward intrusion of Antarctic Intermediate Water. In the midlatitude oceans and in most of the southern part of the Antarctic Circumpolar Current (ACC), was generally upgradient in density on 1000 dbar. Downgradient was found along the North Atlantic Current and Kuroshio Extension as well as in the northern part of the ACC. Zonally integrated meridional transport was poleward at latitudes higher than approximately 40° and equatorward at lower latitudes. The quasi-Stokes or Gent–McWilliams diffusivity coefficient was on the order of 1000 m2 s−1 but was associated with such large uncertainty that it was statistically indistinguishable from zero, except at midlatitudes in the Southern Hemisphere.

Corresponding author address: Katsuro Katsumata, RCGC, JAMSTEC, 2-15 Natsushima, Yokosuka, Japan. E-mail: k.katsumata@jamstec.go.jp
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