Infragravity response to variable wave forcing in the nearshore

Abstract

Analysis of field observations of sea‐surface elevation reveals the role of time‐varying incident forcing and bound wave release mechanisms on the generation of infragravity waves on a barred beach. Observations of infragravity response were obtained during sea breeze and swell periods with wave height varying from 0.2 to 1.2 m and wave period from 3 to 16 s. The observations show a stronger infragravity response to longer period incident swell than to short period wind‐sea. During the peak of the sea breeze, short period wind‐sea is conducive to long wave generation by breakpoint forcing. Under swell‐dominated conditions, the frequency and wave number of incoming bound waves associated with wave groups may satisfy the linear dispersion relationship, leading to resonant forcing of a free wave that appears to be released from the wave group. The transition between long wave generation due to bound wave release and time‐varying breakpoint forcing agrees with the surf beat similarity parameter.