Alleviating the Garden Sprinkler Effect in wind wave models

In ocean wave models, swell propagation at coarse spectral resolution leads to the disintegration of continuous swell fields into discrete swell fields. This process is known as the Garden Sprinkler Effect (GSE). An existing solution to the GSE consists of adding a diffusion tensor to the propagation equation. Although this diffusion method has been proven successful, it is prohibitively expensive for models with high spatial resolution. Two alternatives are presented here. The first is an averaging method. It shares characteristics with the diffusion method, but is much cheaper for high resolution models. The second method consists of adding divergence to the advection field. This divergence method is shown to be accurate for idealized conditions, and requires less tuning, but is still too expensive to replace the other methods in practical conditions. It is therefore suggested to replace the diffusion method with an averaging method in operational models, and to investigate the divergence method further.