Chapter 5. SPATIALLY-COHERENT STRUCTURES
concentrate in the convergence zones. Flotsam makes the bands visible
directly. These bands are sometimes observed even in the absence of floating
objects — compressed films make them visible due to suppressing capillary
waves, thereby giving the bands a smoother appearance in surface
reflectance. In some cases, the amplitude of the surface gravity waves
increases in convergence zones leading to wave breaking. Though
convergences at the ocean surface can be caused by different factors
including internal waves, oceanic fronts, convection etc., Langmuir
circulations are an important and frequent cause of the near-surface
convergence lines.
Figure 5-52. Langmuir cells (dark streaks) in nighttime infrared imagery. The streaks are
about 0.2°C cooler than the ambient surface water. The circle on the right highlights the
termination of one streak. The left circle indicates where two streaks merge. Such features
persisted over several minutes and drifted with the downwind surface current. Bright (warm)
spots occurring throughout the image represent microscale wave breaking events. (This image
is from the public domain of the Naval Research Laboratory Web Site
http://www.nrl.navy.mil.)
The convergence zones are sometimes seen in infrared imagery through
their interaction with the ocean’s cool skin. The infrared imagery shown in
Figure 5-52a depicts long, dark (cool) streaks associated with Langmuir
371
concentrate in the convergence zones. Flotsam makes the bands visible
directly. These bands are sometimes observed even in the absence of floating
objects — compressed films make them visible due to suppressing capillary
waves, thereby giving the bands a smoother appearance in surface
reflectance. In some cases, the amplitude of the surface gravity waves
increases in convergence zones leading to wave breaking. Though
convergences at the ocean surface can be caused by different factors
including internal waves, oceanic fronts, convection etc., Langmuir
circulations are an important and frequent cause of the near-surface
convergence lines.
Figure 5-52. Langmuir cells (dark streaks) in nighttime infrared imagery. The streaks are
about 0.2°C cooler than the ambient surface water. The circle on the right highlights the
termination of one streak. The left circle indicates where two streaks merge. Such features
persisted over several minutes and drifted with the downwind surface current. Bright (warm)
spots occurring throughout the image represent microscale wave breaking events. (This image
is from the public domain of the Naval Research Laboratory Web Site
http://www.nrl.navy.mil.)
The convergence zones are sometimes seen in infrared imagery through
their interaction with the ocean’s cool skin. The infrared imagery shown in
Figure 5-52a depicts long, dark (cool) streaks associated with Langmuir
371