A Numerical Study of Rain-Induced Surface Gravity Wave Attenuation

Strong rain-induced mixing in a thin surface layer is numerically shown to greatly increase surface gravity wave attenuation. This case study uses a single wavelength 2.8 m together with two mixed layer depths 10 and 20 cm. The rain induced mixing is simulated by varying kinematic viscosity within the mixed layer from 0.000001 to 0.01 sq m per sec, molecular to strong turbulent mixing, respectively. The results indicate that surface gravity wave attenuation in the presence of a thin rain induced mixed layer can increase by a factor of up to 6000 times the attenuation rate due to molecular viscosity alone. This indicates that rain need only mix the top 10-20 cm surface layer to effectively dampen short surface gravity waves.