Variations in the atmospheric drag co-efficient due to changes in sea state

Measurements made on both sides of an atmospheric front of the neutral atmospheric drag coefficient, , and ocean surface wave spectra showed a large variation in at constant wind speed that was unexplained by conventional formulations. In our investigation, which for the first time made wave spectral measurements together with correlation flux measurements in the marine surface layer, coincident wave spectral measurements showed an unexpected increase in energy in the 6-sec wave band ( ), which was well correlated with the variation of and the surface roughness, . We derived a relation of to the wave spectra which reduces to Charnock\´s relation in situations of dynamic equilibrium between the wind field and the surface waves. In situations of disequilibrium, the relation shows a strong dependence of on the 6-sec wave field. This relationship of to the surface wave spectra helps explain the apparently high values of behind moving fronts reported in the literature.