Field Evidence of Group Modulation of Open-Ocean Wave Breaking

Abstract:

Open ocean wave breaking (whitecapping) is a highly localized process in both space and time, and is therefore typically quantified using optical measures such as fractional whitecap coverage over an area. Visual observations, theoretical considerations and previous modelling studies give reason to expect that the group structure of surface waves modulates the process of whitecapping by changing the local wave steepness. We present field observations combining platform-based stereo video imagery and optical whitecap coverage that support this hypothesis by exhibiting enhanced instantaneous whitecapping activity within wave groups. We also examine the group-like structure of the instantaneous whitecap coverage in relation to the groupiness of the wave field with ship-based whitecapping measurements and Lagrangian wave buoys. The observational datasets were collected in a wide range of sea states in the central North Sea and the north Pacific Ocean during the winter of 2019-2020.