(*Note on viewing the quicktime movies found here)
(*for Rob's Timeseries Class: see bottom of page)
... And Errata. Please do email me if you catch another mistake, or something that might be a mistake...
The mixing associated with Langmuir circulation can be important in the long-term evolution of the mixed layer. The strength and depth of these structures influence the sea surface temperature, and are important to weather and climate as well as to biology and chemistry.
The following studies are working toward possible interactions between LC and internal waves, based on data from the "Hawaiian Ocean Mixing Experiment" or HOME.
If you are interested in working with the area-mapped surface data (acoustic intensity, related to bubble density; or radial velocity) contact me by email. It is not in a standard form (there is no standard form for this), but we can work out what you need. (see contact info at bottom of page).
A major field experiment called "SandyDuck" took place at the USACE's "Field Research Facility", located near Duck, NC, on the barrier islands off the East Coast of the USA. The focus time ran from September through November, 1997. Many people and many measurements were involved. The goal is to understand the dynamics of flows near shore. These flows are forced by a combination of wave breaking, winds, and topographic effects. Of particular interest is the occurrence, form, and dynamics of rip currents. (Here, "rip currents" are loosely defined as narrow, offshore-directed flows extending some distance seaward from the shore through the surf zone.)
Surface waves are important in many of today's concerns. For example, in planning shipping routes, estimating storm damage risks, and driving coastal erosion. Global models of directional wave spectra are routinely run to assist in these endeavors; however, a model is only as good as the information going into it. The better the observations, the better the results.
Ocean waves can be tricky to measure- the instruments must survive the storms that make the biggest waves. Most modern measurements are fairly simple, giving us estimates of the size of the waves and (perhaps) the mean direction of wave propagation. But to model waves from several storms at once, it would be better to have more detailed directional information. Satellite pictures have great potential in helping with this; however, the "snapshot" pictures of the waves arising from satellites have a 180-degree ambiguity: they can show the orientation of wave crests quite accurately, but cannot tell which direction they are moving. To do that, one needs arrays that resolve the waves in both space and time- for example, Doppler sonar beams extending hundreds of meters along the surface, sampling every second or so.
A major outstanding problem in oceanography lies in understanding the interface between the air and sea. The challenge is to study minute details of the motion there without suffering damage from the large waves.
Some confusion about the interaction of waves and currents arises from the conceptual division of the flow into "Eulerian" (fixed location) versus "Lagrangian" (fluid-following) frameworks. For example, the difference between the mean velocity at a fixed point versus that of a drifting particle is the "Stokes' drift," due to the presence of waves. Often the results of seemingly complex analyses from one viewpoint can be more simply interpreted from the other. In any event, the relation between (often intrinsically Lagrangian) dynamic constraints and the measurements (normally Eulerian) must be borne in mind.
An attempt to write this up in an understandable way:
Smith, J.A., Wave-Current Interactions In Finite-Depth (pdf, 468 kB) vol. 36, no. 7. pp. 1403-1419, J. Phys. Oceanogr., 2006.
and see also:
Smith, J.A., Observed variability of ocean wave Stokes drift and the Eulerian response to passing groups (pdf, 2.6 MB) vol. 36, no. 7, pp. 1381-1402, J. Phys. Oceanogr., 2006.
Please do send suggestions/comments!
Jerome A. Smith, MPL/PORD
Scripps Institution of Oceanography
0213, UCSD
La Jolla, CA 92093-0213
email me: jasmith(at)ucsd.edu
-change (at) to at-sign, this helps defeat web-robots (I wish!)
For Rob's Timeseries Class: notes from 11/26,28,30 - Please check for consistency, and email me if you find any stuff out of place: