WHOI PO

Title: Understanding Interfacial and Sea Spray Heat Fluxes in High Winds Using Direct Covariance Heat Flux Observations
Abstract: Air-sea fluxes of sensible and latent heat are fundamental to the structure and energetics of the air-sea transition zone and storm systems in extreme conditions. In high winds (i.e., 10-m windspeed U10 ≳ 20 m/s), sea spray droplets ejected from breaking wave crests provide pathways for heat transfer via droplet cooling and evaporation that are not represented in the bulk algorithms widely used in extreme weather forecast models for extratropical and tropical cyclones. Sea spray physics is controlled by complex air-sea-wave interactions, but co-located and simultaneous in situ measurements of high-wind environments, spray, and air-sea heat fluxes are extremely limited. Because of this, ongoing challenges remain in robustly demonstrating spray’s presence in high-wind heat flux observations and in calibrating heat flux algorithms for high winds.
In this work, we examine a large and diverse collection of direct covariance (DC) sensible and latent heat flux datasets and compare these fluxes to those computed using the COARE version 3.6 algorithm, a bulk turbulent flux algorithm that does not include spray physics. Observations come from diverse sources, namely the CLIMODE, SPURS 1/2, DYNAMO, FASTEX, and HIWINGS field campaigns and the Pioneer, Endurance, Southern Ocean, and Irminger Sea moored buoys maintained by the Ocean Observatories Initiative. We find a systematic departure of observed heat fluxes from COARE 3.6 calculations in high winds that is consistent with the physics of near-surface spray evaporation. We then incorporate a new model for spray heat fluxes into the COARE algorithm and find that, with minor calibration, the new algorithm reproduces the observed flux behavior well. Finally, we reexamine the interfacial scalar roughness physics of the COARE 3.6 algorithm to determine an optimal interfacial flux model in the presence of spray, highlighting the uncertainty contributed by both spray and interfacial physics in high winds.
These results are promising but are limited by the continued scarcity of DC heat flux, wave, and spray measurements in high winds. This highlights the need for systematic, long-term, and simultaneous high-wind observations of these critical quantities.