Ocean Dynamics
Overall view of the large stratified tank
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Soliton isotherms
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Panoramic radar image of internal solitons.
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NOAA is increasingly monitoring ocean circulation and dynamics by means of remote sensors that probe its surface from ships, aircraft, and satellites. To infer underlying dynamics from the surface properties revealed by radars, radiometers, and lidars requires fundamental advances in our understanding of the surface manifestations of subsurface processes. One example is the way internal waves and long surface waves (swell) modify the short surface waves with which these sensors interact. Without such understanding, the sensors could give incorrect information about the motions of cold and warm currents, the transport of nutrients and pollutants, and air-sea interactions that affect weather and climate.
We combine theoretical studies with laboratory modeling and field experiments at sea to make headway on this extremely complex problem.
Theoretical Studies
Advanced models are needed to describe wave interactions. We are developing such models using both analytical and numerical methods. We have developed a theory of strong internal solitons that shows better agreement with observations than the commonly used model equations. A new numerical algorithm has been developed to simulate this class of processes. For surface waves, we have made progress in describing the modulation of short surface waves by long waves in the presence of turbulent wind. In connection with laboratory experiments, a theory of interactions between internal waves, currents and turbulence has been constructed.
Laboratory Modeling
We collaborate with the Institute of Applied Physics of the Russian Academy of Sciences in Nizhni Novgorod, Russia. This institute has created a unique laboratory complex including two density stratified wave tanks. The larger tank is 20x4x2 m in size, and has a closed wind-wave channel. The larger tank is equipped to simulate a number of processes in the ocean with a scaling of about 1:100 in size and 1:10 in velocity. Unique experimental data have been obtained using these laboratory facilities. Such data includes the distribution of curvatures of surface gravity waves, the evolution of short surface wave packets, redistribution of surface wave amplitudes over an obstacle, and damping of internal and surface waves by turbulence.
The Coastal Ocean Probing Experiment (COPE) was performed in the fall of 1995 by PSD (previously ETL) in collaboration with other institutions, including the Naval Postgraduate School (Monterey, CA) and the Institute of Ocean Sciences (Sidney, B.C., Canada). Extremely strong tidally-generated internal waves in the form of groups of solitary waves (solitons) were observed. They caused a strong modulation of radar signals. Time series of isotherms show thermocline undulations with tidal periods, as well as shorter-period internal-wave fluctuations.