FIELD INVESTIGATION OF INFRAGRAVITY WAVE RESPONSE UNDER SINGLE-PEAKED AND DOUBLE-PEAKED SPECTRAL SEA STATES

Infragravity (hereafter IG) waves are surface gravity waves with typical frequency in the range of 0.005 - 0.04Hz, which are only a few centimeters high in the deep ocean, but amplify rapidly near the coast and can exceed 1 meter in stormy conditions, thus playing an important role in beach and dune erosion. Although the correlation between IG waves and incident short waves has been studied by many scholars before, yet the relationship between the frequency of IG waves and the spectral shape of incident short waves has not been fully understood. In addition, previous studies have often been discussed under single-peaked spectra incident wave conditions, and studies on the IG wave response under double-peaked spectra conditions are scarce. In fact, the probability of double-peaked spectra occurring in real sea states is not low (Soares, 1991). To further investigate the above issues, in this study, we analyzed a dataset collected from the nearshore waters of the North Indian Ocean during the Southwest Monsoon period. The study area was strongly influenced by high-energy swells from the North Indian Ocean during the observation period. while the double-peaked spectra formed by the superposition of the swell energy and the local sea wave energy occurred more often than the single-peaked spectra.