Observations of surf beat

The magnitudes of cross‐shore velocity and elevation oscillations at surf beat frequencies observed on three ocean beaches are significantly correlated with the significant height of incident wind waves. Measured surf beat run‐up spectra are coupled with numerical integrations of the long wave equations to predict the energy spectrum at offshore sensors, and the coherence and phase between offshore sensors and run‐up meter. As in previous studies, valleys in the observed surf beat energy spectra at offshore sensors, and jumps in the relative phase between sensors, occur at the nodal frequencies of simple standing wave (either leaky or high mode edge wave) models. The variance observed in the surf beat cross‐shore velocity field is between 10 and 100 times larger near the shoreline than in 5 m depth, and decays more rapidly with increasing offshore distance than the variance in the surf beat elevation field. The standing wave model is qualitatively consistent with this structure.