Moored turbulence measurements using pulse-coherent doppler sonar
Moored turbulence measurements using pulse-coherent doppler sonar
Date
2021-09-01
Authors
Zippel, Seth F.
Farrar, J. Thomas
Zappa, Christopher J.
Miller, Una
St. Laurent, Louis C.
Ijichi, Takashi
Weller, Robert A.
McRaven, Leah T.
Nylund, Sven
Le Bel, Deborah
Farrar, J. Thomas
Zappa, Christopher J.
Miller, Una
St. Laurent, Louis C.
Ijichi, Takashi
Weller, Robert A.
McRaven, Leah T.
Nylund, Sven
Le Bel, Deborah
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DOI
10.1175/JTECH-D-21-0005.1
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Keywords
Ocean
Turbulence
Atmosphere-ocean interaction
Boundary layer
Oceanic mixed layer
In situ oceanic observations
Turbulence
Atmosphere-ocean interaction
Boundary layer
Oceanic mixed layer
In situ oceanic observations
Abstract
Upper-ocean turbulence is central to the exchanges of heat, momentum, and gases across the air–sea interface and therefore plays a large role in weather and climate. Current understanding of upper-ocean mixing is lacking, often leading models to misrepresent mixed layer depths and sea surface temperature. In part, progress has been limited by the difficulty of measuring turbulence from fixed moorings that can simultaneously measure surface fluxes and upper-ocean stratification over long time periods. Here we introduce a direct wavenumber method for measuring turbulent kinetic energy (TKE) dissipation rates ϵ from long-enduring moorings using pulse-coherent ADCPs. We discuss optimal programming of the ADCPs, a robust mechanical design for use on a mooring to maximize data return, and data processing techniques including phase-ambiguity unwrapping, spectral analysis, and a correction for instrument response. The method was used in the Salinity Processes Upper-Ocean Regional Study (SPURS) to collect two year-long datasets. We find that the mooring-derived TKE dissipation rates compare favorably to estimates made nearby from a microstructure shear probe mounted to a glider during its two separate 2-week missions for O(10−8) ≤ ϵ ≤ O(10−5) m2 s−3. Periods of disagreement between turbulence estimates from the two platforms coincide with differences in vertical temperature profiles, which may indicate that barrier layers can substantially modulate upper-ocean turbulence over horizontal scales of 1–10 km. We also find that dissipation estimates from two different moorings at 12.5 and at 7 m are in agreement with the surface buoyancy flux during periods of strong nighttime convection, consistent with classic boundary layer theory.
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Author Posting. © American Meteorological Society , 2021. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Zippel, S. F., Farrar, J. T., Zappa, C. J., Miller, U., St Laurent, L., Ijichi, T., Weller, R. A., McRaven, L., Nylund, S., & Le Bel, D. Moored turbulence measurements using pulse-coherent doppler sonar. Journal of Atmospheric and Oceanic Technology, 38(9), (2021): 1621–1639, https://doi.org/10.1175/JTECH-D-21-0005.1.
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Zippel, S. F., Farrar, J. T., Zappa, C. J., Miller, U., St Laurent, L., Ijichi, T., Weller, R. A., McRaven, L., Nylund, S., & Le Bel, D. (2021). Moored turbulence measurements using pulse-coherent doppler sonar. Journal of Atmospheric and Oceanic Technology, 38(9), 1621–1639.