Heat Transfer by Thermals in the Convective Boundary Layer
The convective boundary layer (CBL) develops in the atmosphere if turbulence generated by buoyancy due to upward heat flux from the surface dominates relative to turbulence generated by mean shear. The CBL extends from the surface up to an inversion layer at height z i . Above the inversion, the fluid is stably stratified. Turbulence in the mixed layer below the inversion scales with the convective velocity w * = (g β z i Q s )1/3 and the convective temperature T *. = Q s /w *, where g, β, and Q s are the gravitational acceleration, the volumetric expansion coefficient and the temperature flux at the surface, respectively. Typical values in the atmosphere are z i = 1000m, w *. = 1m/s, T * = 0.1K and the related Rayleigh number is of the order 1018, while previous laboratory experiments are limited to Rayleigh numbers less than about 109, e.g. see . The surface layer (0 ≤ z ≤ 0.1z i ,) is affected by the surface roughness height z 0, where z i /z 0 is typically larger than 1000. The surface temperature θ s exceeds the temperature θ m of the mixed layer by an amount ∆θ = θ s − θ m as a function of T *. and z i /z 0.
KeywordsConvection Coherence Stratification Advection
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- 1.R.J. Adrian, R.T.D.S. Ferreira, T. Boberg: Experim. in Fluids 4, 121 (1986)Google Scholar
- 5.R.B. Chatfield, R.A. Brost: J. Geophys. Res. 92, D11, 13263 (1987)Google Scholar
- 10.P.J. Mason: J. Atmos. Sci, in press (1989)Google Scholar
- 11.H. Schmidt: DFVLR-FB-88–30 (1988)Google Scholar
- 12.H. Schmidt, U. Schumann: J. Fluid Mech., in press (1989)Google Scholar