Local Marangoni number at the onset of hydrothermal waves

We report the results of an experiment in which a layer of fluid, placed in a container open to the air, is subjected to a horizontal temperature difference DT. The fluid height h is kept constant and both the horizontal temperature difference and the horizontal dimensions of the fluid layer are changed. In this configuration, when DT goes beyond a certain threshold, waves propagating from the cold to the hot side appear ~hydrothermal waves! with a determined group velocity. We study the influence of the container geometry on these waves. Close to the threshold, they are spatially localized near the hot side and a local Marangoni number is defined to describe this behavior. If DT is further increased, the waves fill the whole fluid layer. We also find an agreement between our experimental results and theoretical works and simulations