With the advent of aircraft early in the century, a need arose to relate air flow drag to aircraft surfaces such as the wings and fuselage. It was quickly demonstrated that the drag coefficient of a boundary layer was related to the roughness of the underlying surface [Nikuradse, 1933], and meteorologists soon were able to develop these ideas for calculating the atmospheric drag over land. A popular concept was aerodynamic roughness length, z0, which can be uniquely related to the drag coefficient under the assumption that the velocity profile in air is logarithmically distributed with height above the surface. This appears quite reasonable in near neutral, steady conditions.
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