EESS talk on "High-resolution observations of internal wave induced turbulence in the deep ocean"
Event details
| Date | 07.03.2017 |
| Hour | 12:15 › 13:15 |
| Speaker |
Dr Hans Van Haren, Senior scientist, Ocean Systems Sciences (OCS), Royal Netherlands Institute for Sea Research - NIOZ, Texel (NL) Short biography: Hans van Haren is a senior scientist at the Royal Netherlands Institute of Oceanography (NIOZ). He graduated from Utrecht University, completing his MsC (physics and geophysics—physical oceanography) in 1985 and PhD in 1990 (working at NIOZ). He worked as a Post-Doc in Canada 1990-1992 with Chris Garrett and Neil Oakey, first at Dalhousie University and Bedford Institute of Oceanography (Halifax), later at University of Victoria (BC). In 1992 he returned to NIOZ, first 3 years as Post-Doc, from 1995 onwards as permanent staff. His work is on ocean observations, including development of new instrumentation, and focusing on the study of turbulent exchange processes governed by internal waves and affecting ocean life. Over the years, he has participated and led more than 50 sea-campaign cruises, varying from shallow seas like the North Sea and Baltic to deep open Atlantic Ocean. |
| Location | |
| Category | Conferences - Seminars |
Abstract:
An overview is presented of high-resolution temperature observations above underwater topography in the deep, stably stratified ocean. The Eulerian mooring technique is used to monitor temperature variations by typically 100 sensors distributed over lines between 40 and 400 m long. The independent sensors sample at a rate of 1 Hz for up to one year with a precision better than 0.1 mK. This precision and sampling rate are sufficient to resolve the large, energy containing turbulent eddies and all of the internal waves and their breaking above underwater topography. Such underwater wave breaking is the key mechanism for the redistribution of nutrients and heat (to maintain the ocean stably stratified), and the resuspension of sediment.
Under conditions of tight temperature-salinity (temperature-density) relationship, the temperature data are used to quantify turbulent overturns. These observations show two distinctive turbulence processes that are associated with different phases of a large-scale (mainly tidal) internal gravity wave: i) highly nonlinear turbulent bores during the upslope propagating phase, and ii) Kelvin-Helmholtz billows, at some distance above the slope, during the downslope phase. While the former may be associated in part with convective turbulent overturning following Rayleigh-Taylor instabilities, the latter are mainly related to shear-induced instabilities. Under weaker stratified conditions, away from boundaries, free convection is the more dominant mixing process observed. With a newly developed five-lines mooring, the transition from isotropy (full turbulence) to anisotropy (stratified turbulence/internal waves) is revealed.
An overview is presented of high-resolution temperature observations above underwater topography in the deep, stably stratified ocean. The Eulerian mooring technique is used to monitor temperature variations by typically 100 sensors distributed over lines between 40 and 400 m long. The independent sensors sample at a rate of 1 Hz for up to one year with a precision better than 0.1 mK. This precision and sampling rate are sufficient to resolve the large, energy containing turbulent eddies and all of the internal waves and their breaking above underwater topography. Such underwater wave breaking is the key mechanism for the redistribution of nutrients and heat (to maintain the ocean stably stratified), and the resuspension of sediment.
Under conditions of tight temperature-salinity (temperature-density) relationship, the temperature data are used to quantify turbulent overturns. These observations show two distinctive turbulence processes that are associated with different phases of a large-scale (mainly tidal) internal gravity wave: i) highly nonlinear turbulent bores during the upslope propagating phase, and ii) Kelvin-Helmholtz billows, at some distance above the slope, during the downslope phase. While the former may be associated in part with convective turbulent overturning following Rayleigh-Taylor instabilities, the latter are mainly related to shear-induced instabilities. Under weaker stratified conditions, away from boundaries, free convection is the more dominant mixing process observed. With a newly developed five-lines mooring, the transition from isotropy (full turbulence) to anisotropy (stratified turbulence/internal waves) is revealed.
Practical information
- General public
- Free
- This event is internal
Organizer
- EESS - IIE
Contact
- Prof. D. Andrew Barry & Dr Andrea Cimatoribus, ECOL