The density of sea water is a function of both temperature and salinity. Increased temperature make water less dense; increased salinity makes water more dense. Vertical changes in density leads to horizontal pressure differences and thus to horizontal motion. Density changes can rise due to difference in temperature with depth or salinity or both. In this experiment we explore the effect of such variations.
Apparatus consists of two vertical, cylindrical acrylic tubes of 3 cm diameter and 30 cm height. The vertical tubes are connected horizontally by two acrylic tubes of 1 cm diameter and 20 cm length. Red and blue dye are needed for coloring the hot and cold, or salty and fresh water columns. The basic setup is show in the Figure to the right. Click on image for better-quality view. |
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Hot-Cold Currents: The left water-column is cooled in an ice bath and blue dye is added and mixed through the column. The right water-column is heated in an 80 ° C bath and red dye is added and mixed through the column. A movie (.avi; 30 MB; you may wish to download the movie before playing) depicts the evolution of this system over a two-minute period (). Observe how the pressure gradient reverses with depth such that the warm water flows right-to-left in the upper-horizontal tube while the cold water flows in the opposite direction in the lower-horizontal tube.
Fresh-Salty Currents: The left water-column is filled with fresh water which has a blue dye already added. The right water-column is filled with salty water which has a red dye already added. A movie (.avi; 20 MB; you may wish to download the movie before playing) depicts the evolution of this system over a two-minute period. Observe how the pressure gradient reverses with depth such that the fresh water flows left-to-right in the upper-horizontal tube while the salty water flows in the opposite direction in the lower-horizontal tube.
A Water-Column apparatus can be acquired from Kelvin Inc.
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