Observations of the Evolution of Turbulent Dissipation within the Ocean Surface Boundary Layer: an OSMOSIS study
Natasha Sarah Lucas1, John Allen2, Stephen E Belcher3, Tim Boyd4, Liam Brannigan5, Mark Inall6, Matthew Palmer7, Jeff Polton7 and Tom Philip Rippeth8, (1)Bangor University, School of Ocean Sciences, Menai Bridge, United Kingdom, (2)University of Portsmouth, United Kingdom, (3)University of Reading, Reading, RG6, United Kingdom, (4)Scottish Association for Marine Science (SAMS), United Kingdom, (5)University of Oxford, Physics, Oxford, United Kingdom, (6)Scottish Association for Marine Science, Oban, United Kingdom, (7)National Oceanography Centre, Liverpool, United Kingdom, (8)Bangor University, School of Ocean Sciences, Bangor, Wales, United Kingdom
Abstract:
This study presents a new 9.5 day dataset showing the evolution of the Ocean Surface Boundary Layer (OSBL) and dissipation of turbulence kinetic energy (TKE), carried out as part of OSMOSIS
[i], at a location in the North East Atlantic Ocean in September 2012. The TKE dissipation measurements were made using three methods; (i) repeated profiling between 100m and the surface by an Ocean Microstructure glider, (ii) three series of profiles made using a loosely tethered velocity microstructure glider and (iii) a moored pulse-pulse coherent high frequency ADCP. Supporting measurements show the evolution of the water column structure, including surface wave measurements from a TRIAXYS wave buoy.
This data shows two distinct regimes; the first, spanning 4 days with relatively low winds, displays a distinct diurnal cycle with the deepening of the active mixing layer during the night which shoaled during the day. The second spanned a significant storm, (with maximum winds speeds reaching ~20 m s-1 and significant wave heights reaching ~6 m), during which, rather than a deepening of the mixed layer as predicted by classical theory, the primary effect was a broadening of the transition layer, similar to that found by Dohan and Davies (2011). During the storm, significant dissipation was observed throughout the surface mixed layer and into the transition layer, driving fluxes of heat downwards through the base of the surface mixed layer.
[i] Ocean Surface Mixing and Submesoscale Interaction Study
Dohan, K. & Davis, R.E., 2011. Mixing in the Transition Layer during Two Storm Events. Journal of Physical Oceanography. 41 (1). pp. 42–66.
