roughness length
Meteorology
noun
A parameter used in representing the variation of horizontal wind speed with height immediately above the ground (or water surface), and typically corresponding to the unevenness of the surface; also surface roughness length.
Origin
1930s; earliest use found in Quarterly Journal of the Royal Meteorological Society. Translating German Linearabmessung der Rauhigkeiten (L. Prandtl 1932, in Beiträge zur Physik der Atmosphäre 19 190.