Waves, rain, and surface roughness at Ocean Station Papa

A combined observational and forecast modeling study will address the coupling between ocean surface waves and rain. The observations will extend an existing time series at Ocean Weather Station Papa (OWS-P) and complement those observations with more detailed measurements using drifting buoys. The observations will be used to improve parameterizations in spectral wind-wave models, as well as fundamental understanding of surface turbulence in the presence of rain and the related changes to air-sea fluxes.

The intellectual merit of this research is addressing a knowledge gap in the suppression of ocean surface waves by rain and the associated changes in surface roughness and surface turbulence. The work will address this gap through long-term field observations at OWS-P, combined with a short-term process study using deployments of opportunity in the same region.

The results will improve understanding of air-sea interactions for coupled climate and forecast models. In particular, this work will enable existing spectral wind-wave forecast models (e.g., WAVEWATCH III, SWAN, etc) to account for the effect of rain on wave generation and dissipation. The broader impacts of this work are in the continuation of a time series of surface waves at a key reference site, as well as improvements to wave forecasting and bulk formulae for air-sea interactions.

Other impacts include undergraduate education, through paid internships each summer (funded directly by the project) and participation in the NSF Research Experiences for Undergraduate program (funded separately). Outreach will be conducted through an updated web site and short videos produced for an existing Applied Physics Lab YouTube channel, as well as booths at public events like Discovery Days (over 10,000 attendees).

The project will test the following hypotheses: 1. Rain suppresses ocean surface waves, especially the short waves in the `tail' of the spectrum. 2. The suppression, together with a reduction in wind input to waves, leads to a reduction in wave breaking. 3. The reduction in wave breaking reduces both the surface roughness (with implications for

drag coefficients) and the surface turbulence (with implications for fluxes). 4. Rain may increase the surface turbulence through a direct injection of turbulence by raindrops, especially in low to moderate winds, competing with the indirect effect of the surface turbulence damping through a reduction in wave breaking.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.