Free convection scaling
From Glossary of Meteorology
free convection scaling
Velocity and length scales that apply to the atmospheric boundary layer during conditions of a statically unstable atmosphere with vigorous thermal circulations and negligible shear-generation of turbulence, such as during a sunny day over land with calm winds.
The length scale is zi, the mixed-layer depth, and the velocity scale is w* the Deardorff velocity. A free convection timescale can be created as t* = zi/w*. A free convection temperature scale 
can be found using the surface kinematic heat flux, 
. Similar scales can be generated for other variables such as humidity.
Stull, R. B. 1988. An Introduction to Boundary Layer Meteorology. 666 pp.
