Researchers

Jim Thomson

Principal Oceanographer

AIRS Department

APL-UW

Associate Professor, Civil and Environmental Engineering

Eric D'Asaro

Senior Principal Oceanographer

OPD Department

APL-UW

Professor, Oceanography

Mike Ohmart

Field Engineer II

OE Department

APL-UW

Joe Talbert

Field Engineer II

AIRS Department

APL-UW

Alex de Klerk

Field Engineer I

AIRS Department

APL-UW

Michael Schwendeman

Research Assistant

AIRS Department

APL-UW

Stephanie Downey

Laboratory Assistant

Funding

NSF

Storm Chasing in the North Pacific

Breaking Wave Dissipation in Mixed Seas

There are very few measurements of waves in the open ocean. Energy really is the key thing we're looking for. To improve the wave forecast for the Navy or the merchant marine, we need to understand how much energy is going into the waves and how much is coming out.

Research Objectives

Our long-term objective is to remotely estimate energy dissipation by wave breaking in the open ocean. Significant progress towards this goal has been made, where we validated remote observations of wind-wave breaking in the absence of swell. We have now extended this research to broad-banded wave fields, that is, mixed seas.

The specific objectives are to:

  • Validate energy dissipation from the Phillips (1985) distribution using simultaneous in situ observations in broad-banded wave fields
  • Determine the dependence of energy dissipation on wave age and frequency-directional spread
  • Test the validity of a commonly used equilibrium approximation, in which energy dissipation is balanced by wind input

Remote observations (digital video recordings) will be processed using a Fourier-based method for breaking crest distribution, which has not yet been applied to broad-banded wave fields. In situ observations (pulse-coherent acoustic Doppler velocity profiles) will be made from a new free drifting platform and be processed using a structure function method.

Quantification of energy dissipation during wave breaking is essential for accurate modeling of waves and the evolution of sea states. Our research expands the validation, while evaluating the dependence of breaking on frequency-directional spreading, wave age, and wind stress. Potential applications of the results include improved global wave models for climate predictions and shipping-naval operations.

Research Cruise Blogs

More About This Research

Publications

Wave breaking dissipation observed by SWIFT drifters

Thomson, J., "Wave breaking dissipation observed by SWIFT drifters," J. Atmos. Ocean. Technol., 29, 1866-1882, doi:10.1175/JTECH-D-12-00018.1, 2012.

More Info

1 Dec 2012

Energy dissipation rates during ocean wave breaking are estimated from high-resolution profiles of turbulent velocities collected within 1 m of the surface.The velocity profiles are obtained from a pulse-coherent acoustic Doppler sonar on a wave-following platform, termed a Surface Wave Instrument Float with Tracking, or "SWIFT", and the dissipation rates are estimated from the structure function of the velocity profiles. The purpose of the SWIFT is to maintain a constant range to the time-varying surface and thereby observe the turbulence in breaking crests (i.e., above the mean still water level). The Lagrangian quality is also useful to pre-filter wave orbital motions and mean currents from the velocity measurements, which are limited in magnitude by phase-wrapping in the coherent Doppler processing. Field testing and examples from both offshore whitecaps and nearshore surf breaking are presented. Dissipation is elevated (up to 10-3 m2 s-3) during strong breaking conditions, which are confirmed using surface videos recorded onboard the SWIFT. Although some velocity contamination is present from platform tilting and heaving, the structure of the velocity profiles is dominated by a turbulent cascade of eddies (i.e., the inertial sub-range). The noise, or uncertainty, in the dissipation estimates is shown to be normally distributed and uncorrelated with platform motion. Aggregated SWIFT measurements are shown to be useful in mapping wave breaking dissipation in space and time.

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