Two dimensional hydrothermal waves in an extended cylindrical vessel

We report experimental results for hydrothermal waves instability in thermocapillary-driven flow in an extended cylindrical geometry. The waves are shown to appear via a supercritical I-o instability. At larger fluid depth, the conventional predictions of Smith and Davis - planar waves referred to as HW1 - are observed. For smaller depth, i.e. for larger aspect ratios, a new kind of spatial behavior is reported which may be interpreted as a new instability. This new instability is localized in the center of the cell and its spatial structure close to onset resembles targets, i.e. purely radial waves. We refer to these hydrothermal waves as HW2.