[original media no longer available]
Here raw footage from NASA’s Cassini and Voyager missions has been combined in a stunning portrait of Saturn and Jupiter. Watch as tiny moons create gravity waves in the rings of Saturn and observe the complicated relative motion between the cloud bands on Jupiter and the swirls and vortices that result. Fluid dynamics are truly everywhere. (Video credit: Sander van den Berg; submitted by Daniel B)
This numerical simulation shows the variation of salinity in the Atlantic Ocean near the mouth of the Amazon River over the course of 36 months. The turbulent mixing of the fresh river water and salty ocean shifts with the ebb and flooding of the river. Salt content causes variations in ocean water density, which can strongly affect mixing and transport properties between different depths in the ocean due to buoyancy. Understanding this kind of flow helps predict climate forecasts, rain predictions, ice melting and much more. (Video credit: Mercator Ocean)
There are many different kinds of sea waves, some of which have fluid dynamical origins and some of which don’t. For example, tsunamis are caused by the sudden displacement of the ocean floor caused by earthquakes and the tides are caused by the pull of the moon on Earth’s oceans. But many of the waves we are accustomed to seeing are caused by the wind moving across open water, whether in the ocean, in a lake or a sea, or even a river or pond. When the wind blows across the free surface of the water, the difference in velocity between the two fluids causes shearing and the development of surface waves as a result of the Kelvin-Helmholtz instability. (Incidentally, this is why other examples of the K-H instability look so much like ocean waves.)
These wind-generated waves can take several forms. Ripples–or capillary waves–remain visible only as long as the wind is blowing. But under steady conditions, or after the wind has affected a large enough area, waves can form that will persist at the surface even if the wind stops blowing. At that point, even though the wind generated the waves, it is gravity that allows them to persist. This is the source of most of the waves we see on large bodies of water. (Photo credit: Travis Weins)