Wave-breaking effects in radar signatures from 2-dimensional modelling of the HI-RES-1 rip feature

Full-spectral modelling of a two-dimensional current structure is used to understand the role of wave-current interaction and wave-breaking (WB) effects in the radar signatures of the rip-like sub-mesoscale feature that were observed during the First High Resolution Remote Sensing (HI-RES-1) experiment. It is found that the large variations in radar cross-section (RCS) in the neighborhood of the cusp-like features within the rip can be reproduced with or without incorporation of wave-breaking (WB) effects. However, when WB effects are not included, consistent with previous models that have used 1-dimensional current structures, in regions away from these cusp-like structures, the composite scattering (CB) model significantly underpredicts the magnitude of the signature. As a consequence, somewhat surprisingly, within the rip, the CB model over-predicts the magnitude of the cusp signature relative to the signature from the rip in non-cusp-like regions. By including WB effects, this deficiency is overcome, and good agreement is obtained. The resulting agreement occurs when the WB effect is based on an estimate of the local critical crest acceleration Ω_c=0.4 g (g=9.8 m/s²) that accompanies the onset of wave-breaking. This value for Ω_c is in good agreement with independently measured values obtained in wave-tank and field experiments. Incorporation of WB effects also eliminates a non-physical dependence on look-angle that occurs when the CB model alone is used