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The Denmark Strait and Other Undersea Overflows The accurate prediction of many important short- and long-range aspects of the global climate, from El Nino to the melting polar ice caps to global warming, depends on models of the ocean and atmosphere which still do not fully capture the physics of some key processes. One example of this is in taking into account the undersea overflow of cold water from the Nordic Sea into the depths of the North Atlantic (see map). Most of the models currently used to simulate global ocean currents either dramatically underestimate the amount of mixing that goes on between these undersea rivers and the overlying water---meaning that too much cold water ends up sitting in the bottom of the North Atlantic; or they overestimate the amount of mixing---suggesting that the rivers completely dissipate into the overlying water very quickly and go nowhere. In situ (but fairly low resolution) measurements of the velocity and density fields in these overflows suggest that their behavior may actually be much more complicated. They may, in fact, go through various stages as the mixing itself alters the system parameters: sometimes entraining the bulk overlying fluid into the moving river; other times releasing initially fast-moving parts of the undersea current into the bulk fluid (detrainment).		Our goal is to experimentally investigate this mixing process in the laboratory where very precise measurements of the density and velocity fields can be made simultaneously. A number of preliminary images visualizing the temperature field using thermochromic liquid crystals are shown here. After calibration, the color information from these images can be mapped directly into fluid density fields. Things only get more interesting as we add in the simultaneous measurement of the velocity field using particle tracking velocimetry (from a similar convecting fluid experiment). More to come soon!
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Quasi-two-dimensional turbulence on the surface of Jupiter as seen from Galileo (NASA).