Instability of the thermal bar formed in a gravity current

The results of experiments concerning fresh water at the temperature more than 4°C released along a free surface into water with a temperature less than 4°C are presented. As a result of Relay-Taylor instability caused by the nonmonotonic dependence of water density on the temperature, the denser water initially sank to the inclined bottom. At the same time, a vertical front separating water masses less and greater than 4°C formed. In limnology such an effect is called the “thermal bar.” Under certain conditions along with the Relay-Taylor instability, the Kelvin-Helmholtz instability tending to destroy the vertical front was also observed. Corresponding illustrations are presented.