Glider Observations of the North Equatorial Current in the Western Tropical Pacific
Journal Article - Open Access
SCRIPPS INSTITUTION OF OCEANOGRAPHY LA JOLLA CA LA JOLLA United States
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The North Equatorial Current NEC of the Pacific Ocean advects subtropical, subpolar, and tropical water masses. Repeat underwater glider observations of the NEC from June 2009 to January 2014 along 134.38E provide absolute zonal geostrophic velocity, transport, and water mass structure at length scales of 101000 km. The NEC is strongest near the surface and persistent eastward undercurrents are identified deeper than potential density surface 26 kg m23 at 9.68N and 13.18N. Mean transport from the surface to 27.3 kg m23 and 8.58N16.58N is 37.6 Sv 106 m3 s21, with a standard deviation of 15.6 Sv. The transport variability is greatest deeper than 26 kg m23 due to undercurrent variability. Wavelet analysis at scales of 1080 km reveals extrema of fine-scale salinity variance along isopycnals spice variance. High spice variance is found in the North Pacific Tropical Water NPTW and the North Pacific Intermediate Water NPIW, with a spice variance minimum between water masses at 25.5 kg m23. A horizontal Cox number, CH, relates salinity variance at fine scales 1080 km to that at greater length scales 120200 km. As a function of density, CH is nearly vertically uniform, indicating that the stirring of mean salinity gradients enhances fine-scale salinity variance. NPTW, with an estimated horizontal eddy diffusivity of order 104 m s22, is a useful tracer for the region and may be used to relate the fine-scale salinity variance to an eddy diffusivity.
- Physical and Dynamic Oceanography