I am currently researching internal waves.

Here is a good picture of a few interacting IW packets:

Internal Waves, Baja Peninsula, Mexico, October 1994. In the sun-glint, bands of internal waves can be seen approaching the Baja Peninsula near Point Prieta in Mexico in this north-looking low-oblique view. The area of the band of internal waves is just to the north of the Bay of Sebastian Vizcaino. Internal Waves are located just below the sea surface from near 10 feet (3 meters) to over 300 feet (92 meters). They are most obvious at a density interface within the ocean, such as, the base of the upper mixed layer of thermocline. The spacing of these internal waves can vary from over 1 mile (1.6 km) to 5 miles (8 km) and they usually occur in packs of four to eight waves per packet. Oceanographers became aware of internal waves in 1975 when they were photographed in the Andaman Sea by astronauts on the Apollo-Soyuz Mission.

ref: http://209.15.138.224/inmomex/s_dInternalWaves1.htm

How internal waves work:

Internal waves are gravity waves that oscillate due to buoyancy. The simplest example is a wave propagating at the interface between two fluids of different densities, such as oil and water. Internal waves typically have much lower frequencies and higher amplitudes than surface gravity waves because the density differences (and therefore the restoring forces) within a fluid are usually much smaller than the density of the fluid itself.

The atmosphere and ocean are continuously stratified: potential density generally increases with depth. Internal waves in a continuously stratified medium may propagate vertically as well as horizontally. The dispersion relation for such waves is curious: the direction of propagation of energy (group velocity) is perpendicular to the direction of propagation of wave crests and troughs (phase velocity).

Internal waves at tidal frequencies are produced by tidal flow over topography/bathymetry, and are known as internal tides. Nonlinear solitary internal waves are called solitons.

ref: http://en.wikipedia.org/wiki/Internal_wave