Award Abstract # 1434694
Collaborative Research: A Lagrangian Description of Breaking Ocean Surface Waves from Laboratory Measurements and Stochastic Parameterizations.

NSF Org: OCE
Division Of Ocean Sciences
Recipient: UNIVERSITY OF CALIFORNIA SAN DIEGO
Initial Amendment Date: July 1, 2014
Latest Amendment Date: July 1, 2014
Award Number: 1434694
Award Instrument: Standard Grant
Program Manager: Eric C. Itsweire
OCE
 Division Of Ocean Sciences
GEO
 Directorate for Geosciences
Start Date: October 1, 2014
End Date: September 30, 2017 (Estimated)
Total Intended Award Amount: $479,490.00
Total Awarded Amount to Date: $479,490.00
Funds Obligated to Date: FY 2014 = $479,490.00
History of Investigator:
  • W Melville (Principal Investigator)
    kmelville@ucsd.edu
Recipient Sponsored Research Office: University of California-San Diego Scripps Inst of Oceanography
8622 DISCOVERY WAY # 116
LA JOLLA
CA  US  92093-1500
(858)534-1293
Sponsor Congressional District: 50
Primary Place of Performance: University of California-San Diego Scripps Inst of Oceanography
CA  US  92093-0213
Primary Place of Performance
Congressional District:
50
Unique Entity Identifier (UEI): QJ8HMDK7MRM3
Parent UEI: QJ8HMDK7MRM3
NSF Program(s): PHYSICAL OCEANOGRAPHY
Primary Program Source: 01001415DB NSF RESEARCH & RELATED ACTIVIT
Program Reference Code(s):
Program Element Code(s): 161000
Award Agency Code: 4900
Fund Agency Code: 4900
Assistance Listing Number(s): 47.050

ABSTRACT

Wave breaking effects are important in many areas of atmospheric and ocean sciences, including air-sea interaction and momentum, energy and biogeochemical fluxes; hurricane dynamics and thermodynamics; pollutant transport and dispersion; aerosol production and ocean acoustics, to name a few. The goal of this collaborative research is to build a stochastic Lagrangian parameterization of surface wave breaking that can subsequently be applied to wave and ocean modeling. The students and postdoctoral researchers employed in this project will gain experience in the disciplines of science, technology, engineering and mathematics (STEM). The data and breaking parameterization developed here will subsequently find direct application in atmosphere and ocean modeling.

Increases in the fidelity and resolution of ocean models, specifically those focused on the sub-mesoscales, require improved representation of surface wave processes. In addition to the importance of wave breaking in the dynamics of wave-current interaction, it also plays an important role in mass transport beyond that represented in classical theories of Stokes drift; in the dynamics and kinematics of Langmuir turbulence; and, more generally, in the transport and dispersion of tracers and pollutants. This research involves laboratory experiments to measure the Lagrangian displacement and velocity of fluid particles in breaking waves. The data will then be used to develop and parameterize a stochastic ordinary differential equation, within the class of Langevin equations, to describe the Lagrangian motion of the fluid elements. The parameterization will be constrained by the n-point structure functions for the experimentally obtained particle paths, which are comparatively easier to obtain and to relate to a stochastic ordinary (Lagrangian) differential equation, when compared to obtaining the n-point structure function of an (Eulerian) stochastic partial differential equation. Given the Lagrangian model, a projection to the Eulerian frame will be used to obtain the dynamical representation of breaking for wave-current interaction and other mixed-layer processes.

PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH

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Deike, L., Melville, W.K. & Popinet, S. "Air entrainment and bubble statistics in three dimensional breaking waves" Journal of fluid mechanics , v.801 , 2015 , p.91
Deike, L., Pizzo, N.E., Melville, W.K. "Lagrangian transport by breaking waves." Journal of Fluid Mechanics , v.829 , 2017 , p.364
Deike, L., Popinet, S. & Melville,W.K. "Capillary effects on wave breaking" Journal of Fluid Mechanics , v.769 , 2015 , p.541
N. Pizzo, L. Deike and W.K. Melville "Current generation by deep-water breaking waves." Journal of Fluid Mechanics , v.803 , 2016 , p.275
Pizzo, N.E. "Surfing surface gravity waves" Journal of Fluid Mechanics , v.823 , 2017 , p.316

PROJECT OUTCOMES REPORT

Disclaimer

This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.

Objects floating on the ocean surface are transported by a "Stokes drift" due to the slightly open orbits of the fluid motion associated with the waves. This motion is illustrated by the particle paths in Figure 1a for unbroken waves. The Stokes drift is important for a number of processes in the surface layers of the ocean, including the dispersion of pollutants. But it has been an open question as to what the drift is if the waves are breaking, and how it may be parameterized in ocean models. This was the focus of this project, conducted in collaboration with Prof. Juan Restrepo at Oregon State University.

 It was originally intended to conduct laboratory experiments on the breaking problem at Scripps Institution of Oceanography, UC San Diego,  but the need to construct a new experimental facility during the course of this project forced us to resort to numerical experiments, as demonstrated in Figure 1. Figure 1b shows an example of fluid particle paths in a breaking wave packet. Note the large displacement as a wave packet focuses and breaks; significanly different from the unbroken case in Figure 1a. These data may be processed to measure an average drift velocity plotted versus a characteristic slope of the waves, S. These results are shown in Figure 2 where for small slopes (unbroken waves) the drift velocity is approximately proportional to the slope squared, consistent with Stokes drift, whereas for larger slopes (breaking waves) it is proportional to the slope. This is the primary result of this project.

The fact that the drift in breaking waves is proportional to the slope is consistent with a theory of the onset of breaking also developed during this project.

These results are currently being used to consider an improved model of surface drift in more realistic ocean models. Such models have application to better understanding the generation of ocean currents, the dynamics and mixing of the upper ocean, and the dispersion of pollutants at the ocean surface.

 

 

 


Last Modified: 01/28/2018
Modified by: W K Melville

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