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Lateral diffusivity from tracer release experiments in the tropical North Atlantic thermocline
Author(s) -
Banyte Donata,
Visbeck Martin,
Tanhua Toste,
Fischer Tim,
Krahmann Gerd,
Karstensen Johannes
Publication year - 2013
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/jgrc.20211
Subject(s) - tracer , thermocline , thermal diffusivity , upwelling , zonal and meridional , geology , eddy diffusion , sampling (signal processing) , jet (fluid) , geophysics , climatology , oceanography , meteorology , mechanics , turbulence , physics , thermodynamics , nuclear physics , optics , detector
Lateral diffusivity is computed from a tracer release experiment in the northeastern tropical Atlantic thermocline. The uncertainties of the estimates are inferred from a synthetic particle release using a high‐resolution ocean circulation model. The main method employed to compute zonal and meridional components of lateral diffusivity is the growth of the second moment of a cloud of tracer. The application of an areal comparison method for estimating tracer‐based diffusivity in the field experiments is also discussed. The best estimate of meridional eddy diffusivity in the Guinea Upwelling region at about 300 m depth is estimated to beK y = 500 ± 200 m 2 s −1 . The zonal component of lateral diffusivity is estimated to beK x = 1200 ± 600 m 2 s −1 , while areal comparison method yields areal equivalent zonal diffusivity component ofK x e = 1000 ± 500 m 2 s −1 . In comparison to K y , K x is about twice larger, resulting from the tracer patch stretching by zonal jets. Employed conceptual jet model indicates that zonal jet velocities of about 0.015 ± 0.005 m s −1 are required to explain the enhancement of the zonal eddy diffusivity component. Finally, different sampling strategies are tested on synthetic tracer release experiments. They indicate that the best sampling strategy is a sparse regular sampling grid covering most of the tracer patch.