Absolute and convective instabilities of the natural convection in a vertical heated slot

The spatiotemporal instability of a natural convection flow in vertical heated slot is studied theoretically. The two unstable modes, secondary cell and traveling wave, are illustrated to be absolute and convective instabilities, respectively. Using a model to simulate the temperature gradient in the center of the slot, we propose an interpretation of the mechanism controlling the reverse transition of flow patterns, and explain the temperature fluctuation observed after the reverse transition in terms of the traveling wave mode.