Abstract. Surfactant layers with viscoelastic properties floating on the
water surface dampen short gravity-capillary waves. Taking advantage of the
known virtue of fish oil to still angry seas, a laboratory study has been
made to analyse wind-wave generation and the interaction between wind
waves, paddle waves, and airflow. This was done in a tank containing a thin
fish-oil film uniformly spread on the water surface. The research was aimed,
on the one hand, at quantifying for the first time the effectiveness of this
surfactant at impeding the generation of wind waves and, on the other, at
using the derived conditions to disentangle relevant mechanisms involved in
the air–sea interaction. In particular, our main interest concerned the
processes acting on the wind stress and on the wave growth. With oil
on the water surface, we have found that in the wind-only condition (no
paddle waves) the wave field does not grow from the rest condition. This
equilibrium is altered by irregular paddle (long) waves, the generation and
evolution of short waves (in clean water and with oil) being modified by
their interaction with the orbital velocity of the long waves and their
effect on the airflow. Paddle waves do grow under the action of wind, the amount being similar in clean and oily water conditions, a fact we ascribe to
the similar distortion of the wind vertical profile in the two cases. We
have also verified that the wind-supported stress on the oily water surface
was able to generate a surface current, whose magnitude turns out to be
comparable to the one in clean water. We stress the benefits of experiments
with surfactants to explore in detail the physics at, and the exchanges
across, the wavy and non-wavy air–water interface.
Analysis of the effect of fish oil on wind waves and implications for air–water interaction studies