roughness sublayer
From Glossary of Meteorology
(Same as transition layer.) The lowest atmospheric layer immediately adjacent to a surface covered with relatively large roughness elements such as stones, vegetation, trees, or buildings.
The roughness sublayer extends from the surface up to about two to five times the height of the roughness elements and includes the canopy layer. Within the roughness sublayer the flow is three-dimensional, since it is dynamically influenced by length scales of individual roughness elements and surface layer scaling cannot be expected to apply.
Compare aerodynamic roughness length.
