SOME ASPECTS OF THE DECAY OF CONVECTIVE TURBULENCE

The decay of temperature and velocity fluctuations in a convective tur bulent 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 th at, when the cooling rate \dT(s)/d(t)\ is maintained constant, the dec ay times of turbulent velocity and temperature fields, from the initia tion of cooling, scale with Delta T-0/\dT(s)/dt\, where aro is the tem perature difference between the cooling surface and the mixed layer, i rrespective of the Prandtl number. Mechanistic explanations are provid ed to describe the experimental observations. Geophysical relevance of the results is also discussed by considering the dissolution of the a tmospheric convective boundary layer. (C) 1998 The Japan Society of Fl uid Mechanics Incorporated and Elsevier Science B.V. All rights reserv ed.