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The decay of temperature and velocity uctuations in a convective turbulent boundary layer over a heated surface in response to cooling at the surface was studied using a laboratory experiment. The time scale associated with cooling was greater than the relaxation time scale of turbulence, whereupon the convective layer responds to the changes of thermal forcing in a series of quasi-stationary steps. It was found that, when the cooling rate |dT s=dt| is maintained constant, the decay times of turbulent velocity and temperature ÿelds, from the initiation of cooling, scale with T0=|dTs=dt|, where T0 is the temperature di erence between the cooling surface and the mixed layer, irrespective of the Prandtl number. Mechanistic explanations are provided to describe the experimental observations. Geophysical relevance of the results is also discussed by considering the dissolution of the atmospheric convective boundary layer.

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