Spectral Characteristics of Gravity‐Capillary Waves, With Connections to Wave Growth and Microbreaking

Abstract

AbstractIn order to improve our understanding of physical air‐sea interaction, it is essential to better describe the short‐scale ocean wave response to wind forcing. This is particularly true for waves which are small enough to evade observation by traditional buoy and point‐based gauge measurements but large enough to appreciably alter the transfer of momentum between atmosphere and ocean. Such waves are restored to equilibrium both by the Earth's gravity and air‐sea surface tension, hence the classification as “gravity‐capillary.” Radar remote sensing techniques depend greatly upon these waves in order to extract useful physical parameters from afar. Despite this importance, field observations of gravity‐capillary wave characteristics are uncommon and results vary from study to study. Furthermore, leading‐edge model wave number spectra generally do not match each other in shape or important spectral parameters. Here we present an extended analysis of short wave data collected via a polarimetric camera aboard Research Platform Floating Instrument Platform in the Santa Barbara Channel. Our wave number saturation spectra show the emergence of a peak in the gravity‐capillary subrange at low wind forcing magnitude (u*~0.045 m/s), consistent with critical wave growth in air side stability theory and previously only observed in the laboratory. Finally, the effects of microbreaking on wave spectral characteristics are discussed.