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Evaluating Langmuir turbulence parameterizations in the ocean surface boundary layer
Author(s) -
Sutherland G.,
Christensen K. H.,
Ward B.
Publication year - 2014
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2013jc009537
Subject(s) - turbulence , boundary layer , langmuir turbulence , planetary boundary layer , environmental science , surface (topology) , surface layer , atmospheric sciences , mechanics , meteorology , langmuir , layer (electronics) , geology , physics , materials science , mathematics , geometry , chemistry , nanotechnology , aqueous solution
Abstract It is expected that surface gravity waves play an important role in the dynamics of the ocean surface boundary layer (OSBL), quantified with the turbulent Langmuir number ( L a =u * / u s 0, whereu *andu s 0are the friction velocity and surface Stokes drift, respectively). However, simultaneous measurements of the OSBL dynamics along with accurate measurements of the wave and atmospheric forcing are lacking. Measurements of the turbulent dissipation rate ϵ were collected using the Air‐Sea Interaction Profiler (ASIP), a freely rising microstructure profiler. Two definitions for the OSBL depth are used: the mixed layer derived from measurements of density ( h ρ ) , and the mixing layer ( h ϵ ) determined from direct measurements of ϵ . When surface buoyancy forces are relatively small, ϵ ∝ L a − 2only near the surface with no dependency on La at mid‐depths of the OSBL when usingh ρas the turbulent length scale. However, ifh ϵis used then the dependence of ϵ with L a − 2is more uniform throughout the OSBL. For relatively high destabilizing surface buoyancy forces, ϵ is proportional to the ratio of the OSBL depth against the Langmuir stability length L L . During destabilizing conditions, the mixed and mixing layer depths are nearly identical, but we have relatively few measurements under these conditions, rather than any physical implications. Observations of epsilon are compared with the OSBL regime diagram of Belcher et al. (2012) and are generally within an order of magnitude, but there is an improved agreement ifh ϵis used as the turbulent length scale rather thanh ρ .