Influence of surface forcing on near-surface and mixing layer turbulence in the tropical Indian Ocean |
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| Institution: | 1. School of Physics, Ryan Institute, National University of Ireland, Galway, Ireland;2. Scripps Institution of Oceanography, San Diego, USA;3. Sorbonne Universités (UPMC, Univ Paris 06)-CNRS-IRD-MNHN, LOCEAN Laboratory, IPSL, Paris, France;1. INRIA Rennes-Bretagne Atlantique, campus de Beaulieu, 35042 Rennes, France;2. LIRNE-EIMA, Ibn Tofaïl University, B.P. 133, 14 000 Kenitra, Morocco;1. School of Materials Science and Engineering, Sichuan University, Chengdu 610065, PR China;2. Center for Superconducting and Magnetic Materials, Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore;3. Temasek Laboratories, National University of Singapore, 5A Engineering Drive 2, Singapore 117411, Singapore;4. Key Laboratory of Advanced Special Material & Technology, Ministry of Education, Chengdu 610065, PR China;1. Departamento de Química Física, Universidad Complutense, 28040 Madrid, Spain;2. Laboratoire Colisions, Agrégats et Reactivité, UMR 5589, IRSAMC, Université Paul Sabatier, 31062 Toulouse, France;1. LMGC, UMR CNRS 5508, Université Montpellier-2, case courier 048, place Eugène-Bataillon, 34095 Montpellier cedex 5, France;2. Department of Mathematics, Faculty of Science, Mahidol University, Bangkok 10400, Thailand;3. Centre of Excellence in Mathematics, CHE, Bangkok 10400, Thailand;4. Departamento de Matemáticas, Universidad de los Andes, Cra 1 No 18A-12, Bogota, Colombia;1. LMGC, UMR-CNRS 5508, Université Montpellier-2, case courier 048, place Eugène-Bataillon, 34095 Montpellier cedex 5, France;2. Department of Mathematics, Faculty of Science, Mahidol University, Bangkok 10400, Thailand;3. Centre of Excellence in Mathematics, CHE, Bangkok 10400, Thailand |
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| Abstract: | An autonomous upwardly-moving microstructure profiler was used to collect measurements of the rate of dissipation of turbulent kinetic energy (ε) in the tropical Indian Ocean during a single diurnal cycle, from about 50 m depth to the sea surface. This dataset is one of only a few to resolve upper ocean ε over a diurnal cycle from below the active mixing layer up to the air–sea interface. Wind speed was weak with an average value of ~5 m s?1 and the wave field was swell-dominated. Within the wind and wave affected surface layer (WWSL), ε values were on the order of 10?7–10?6 W kg?1 at a depth of 0.75 m and when averaged, were almost a factor of two above classical law of the wall theory, possibly indicative of an additional source of energy from the wave field. Below this depth, ε values were closer to wall layer scaling, suggesting that the work of the Reynolds stress on the wind-induced vertical shear was the major source of turbulence within this layer. No evidence of persistent elevated near-surface ε characteristic of wave-breaking conditions was found. Profiles collected during night-time displayed relatively constant ε values at depths between the WWSL and the base of the mixing layer, characteristic of mixing by convective overturning. Within the remnant layer, depth-averaged values of ε started decaying exponentially with an e-folding time of 47 min, about 30 min after the reversal of the total surface net heat flux from oceanic loss to gain. |
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| Keywords: | Dissipation of turbulent kinetic energy Near-surface turbulence Remnant layer Dissipation decay time Air-Sea Interaction Profiler (ASIP) Diurnal cycle Wind-driven mixing Convectively-driven mixing |
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