Ocean Swell: its Decay and Period Increase

Abstract

HITHERTO there has been a difference of opinion concerning the role of eddy viscosity in the behaviour of wind waves and swell. On one hand, Suthons¹ ascribes the lengthening of waves in sea and swell and part of the decay of swell to the effect of eddy viscosity. According to Suthons, waves become longer simply because viscosity tends to increase the depth of water affected by the wave motion, since it transfers kinetic energy downwards. This reasoning does not, however, seem convincing. Obviously, longer waves have greater depths of water affected by the wave motion; but this does not mean that, conversely, the waves would become longer if the depth of water having kinetic energy were increased by effects that have nothing to do with the mechanism of wave motion.