It is shown that the observationally determined roughness relation z0 = αu*2/g in which g is the acceleration of gravity, u*, is the friction velocity in air, and α = 0.0185 (Wu, 1982) for the wind profile over the sea surface relative to the surface current, is consistent with the existence of a Richardson Number criterion at the air-sea interface in which the critical Richardson Number, Ric = 1, such that all the shear energy is converted into potential energy.