Ocean Gravity-Capillary Waves: Dependence on Sea-Surface Processes and Microlayer Properties

Lead PI: Dr. Christopher J. Zappa , Nathan J.M. Laxague

Unit Affiliation: Ocean and Climate Physics, Lamont-Doherty Earth Observatory (LDEO)

September 2019 - August 2021
Project Type: Research

DESCRIPTION: Poor understanding of ten centimeter and shorter waves, termed 'gravity-capillary' and 'capillary' waves, remains a point of weakness in modern wave models. Adequate characterization of these waves and their response to wind forcing is essential to understand how momentum, heat and gases are transferred between the atmosphere and ocean. The presence of surfactants on the ocean surface has long been understood to damp such waves, but direct observations of this effect in the real ocean remain exceedingly rare. The physical process of rain impacting the ocean surface also affects surface gravity-capillary waves, though observations of this interaction in the real ocean do not yet exist. This project is to analyze an underutilized data set collected at sea with state-of-the-art observational systems, describing short wave properties of the sea surface, and incorporating sea surface microlayer chemical properties. These data will allow a better description of gravity-capillary waves and the air-sea fluxes they mediate over a variety of environmental conditions, and help improve existing models. The results from the data will be used to create stimulating teaching materials through the Earth2Class (E2C) Workshops for Educators, a professional development program for teachers which reaches school districts with large numbers of students from underrepresented groups. Workshop results will be shared through the E2C website, and team members will also present public lectures to reach a non-classroom audience.

The overall body of measurements of these waves in the real ocean is quite small, owing to the difficulty in observing them using traditional techniques. This has led to a paucity of descriptions of gravity-capillary wave response to atmospheric forcing, changes in sea surface chemistry, and disruptive physical processes such as rain. The novel dataset to be utilized included observations of fine-scale wind wave characteristics made simultaneously with measurements of sea surface microlayer (SSML) chemical and biological properties. This study will test three hypotheses focused on short-scale ocean waves, how they grow due to wind forcing, how they are attenuated by surfactants, and the ways in which they are impacted by rain. This work will greatly expand our understanding of short ocean waves characteristics, producing a rich base of gravity-capillary wave observations which will be invaluable to future wave modeling efforts. Incorporation of the SSML chemical and biological properties into this analysis will produce a first-of-its-kind study of the scale-dependent response of gravity-capillary ocean waves to changes in surface chemistry and the SSML microbiome. Analyses of the impact of rain on these short waves will provide further insight into physical processes whose mechanistic descriptions are both underrepresented in the literature and increasingly found to be of importance to physical air-sea interaction.