Observations of whitecaps during HiWinGS, their dependence on wave field, and relation to gas transfer velocities
Abstract:
Taking advantage of the range of physical forcing and wave conditions sampled during HiWinGS, we investigate how the fractional whitecap coverage (W) and gas transfer velocity (K) vary with sea state. We distinguish between windseas and swell based on a separation algorithm applied to directional wave spectra, allowing contrasting pure windseas to swell dominated periods. For mixed seas, system alignment is considered when interpreting results.
The four gases sampled during HiWinGS ranged from being mostly waterside controlled to almost entirely airside controlled. While bubble-mediated transfer appears to be small for moderately soluble gases like DMS, the importance of wave breaking turbulence transport has yet to be determined for all gases regardless of their solubility. This will be addressed by correlating measured K to estimates of active whitecap fraction (WA) and turbulent kinetic energy dissipation rate (ε). WA and ε are estimated from moments of the breaking crest length distribution derived from the imagery, focusing on young seas, when it is likely that large-scale breaking waves (i.e., whitecapping) will dominate the ε.