Thread-shaped intensity field after light propagation through the convective cell

A thread-shaped intensity field has been observed at 2 m distance when a laser beam passed through a water convection cell with characteristic Rayleigh number about 10^{8}. Similar intensity fields were simulated by using phase screen method for various turbulent spectrum in the cell. We show that experimental result can be described by Tatarskii spectrum which take into account the inner scale.