Wave Age

Wave age is the ratio of the phase speed of the dominant waves to the wind speed (c_p / U), a dimensionless measure of how developed a sea state is relative to the wind forcing it. Young, growing wind seas have wave age below about 1.2, where waves travel slower than the wind and absorb momentum from it; a fully developed sea reaches wave age near 1.2, and swell that outruns the local wind has wave age above 1.2. Wave age controls the sea-surface roughness and the drag coefficient: younger, steeper seas are rougher and raise the wind stress, which couples the wave field to the momentum flux in the marine boundary layer.