Mixed and mixing layer depths in the ocean surface boundary layer under conditions of diurnal stratification

Type Article
Date 2014-12
Language English
Author(s) Sutherland G.1, Reverdin Gilles2, Marie Louis3, 4, Ward Ben1
Affiliation(s) 1 : Natl Univ Ireland, Sch Phys, Galway, Ireland
2 : Univ Paris 06, Univ Sorbonne,Paris VI Denis Diderot Univ, Denis Diderot Univ,CNRS,IRD,MNHN, LOCEAN,Inst Pierre Simon Lapl Expt & Approches Nu, F-75252 Paris 05, France
3 : UBO, IRD, IFREMER, Lab Phys Oceans,UMR 6523,CNRS, Plouzane, France
4 : Ifremer, France
Source Geophysical Research Letters (0094-8276) (Amer Geophysical Union), 2014-12 , Vol. 41 , N. 23 , P. 8469-8476
DOI 10.1002/2014GL061939
WOS© Times Cited 33
Keyword(s) ocean surface boundary layer, mixed and mixing layer depths, buoyancy
Abstract A comparison between mixed (MLD) and mixing (XLD) layer depths is presented from the SubTRopical Atlantic Surface Salinity Experiment (STRASSE) cruise in the subtropical Atlantic. This study consists of 400 microstructure profiles during fairly calm and moderate conditions (2 < U10 < 10 m s−1) and strong solar heating O(1000 W m−2). The XLD is determined from a decrease in the turbulent dissipation rate to an assumed background level. Two different thresholds for the background dissipation level are tested, 10−8 and 10−9 m2 s−3, and these are compared with the MLD as calculated using a density threshold. The larger background threshold agrees with the MLD during restratification but only extends to half the MLD during nighttime convection, while the lesser threshold agrees well during convection but is deeper by a factor of 2 during restratification. Observations suggest the use of a larger density threshold to determine the MLD in a buoyancy driven regime.
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