Parameterizations and Algorithms for Oceanic Whitecap Coverage

Abstract

Shipboard measurements of fractional whitecap coverage W and wind speed at 10-m height, obtained during the 2006 Marine Aerosol Production (MAP) campaign, have been combined with ECMWF wave model and Quick Scatterometer (QuikSCAT) satellite wind speed data for assessment of existing W parameterizations. The wind history trend found in an earlier study of the MAP data could be associated with wave development on whitecapping, as previously postulated. Whitecapping was shown to be mainly wind driven; for high wind speeds (.9 m s 21 ), a minor reduction in the scatter of in situ W data points could be achieved by including sea state conditions or by using parameters related to wave breaking. The W values were slightly larger for decreasing wind/developed waves than for increasing wind/developing waves, whereas cross-swell conditions (deflection angle between wind and swell waves between 6458 and 61358) appeared to dampen whitecapping. Tabulated curve fitting results of the different parameterizations show that the errors that could not be attributed to the propagation of the standard error in U 10 remained largely unexplained. It is possible that the counteracting effects of wave development and cross swell undermine the performance of the simple parameterizations in this study.

The FuGas 2.3 Framework for Atmosphere–Ocean Coupling: Comparing Algorithms for the Estimation of Solubilities and Gas Fluxes

“…This fits the general theory that under low-moderate wind speeds, the k w is set by surface renewal and micro-scale wave breaking (i.e., by k wind ), increasing with steeper younger waves [28,51,65], and only under higher wind speeds is k w set by bubbles from breaking waves (i.e., k bubble ) [41][42][43][44][45][46][47][48][49][50]. The preponderance of surface renewal and micro-scale wave breaking at the coastal ocean turn it more susceptible to additional factors driving k w .…”

“…We rejected periods for which there were abrupt changes in wind speed or direction as these represented strong violations of the required homogeneous conditions [77]. An extra filter was applied to remove measurements in which wave age denoted large dominance of swell conditions (β > 2), since they have been identified as biasing measurements of transfer velocity [47,48]. When the ratio is >1 the waves move faster than the wind, indicating the presence of swell [47,48].…”

“…An extra filter was applied to remove measurements in which wave age denoted large dominance of swell conditions (β > 2), since they have been identified as biasing measurements of transfer velocity [47,48]. When the ratio is >1 the waves move faster than the wind, indicating the presence of swell [47,48]. Using only the observations passing the quality control check, the air-water CO 2 fluxes measured by eddy-covariance were smoothed over 30 min bins and corrected according to the Webb-Pearman-Leuning (WPL) method [78].…”

“…Such are the formulations proposed by Carini et al [30] or Raymond and Cole [31], accounting only for u 10 , or by Borges et al [32], adding current drag with the bottom. Meanwhile, new evidence emerged for the effects of the sea surface cool-skin and warm-layer [33][34][35][36][37][38], atmospheric stability [39,40], wave-breaking [41][42][43][44][45][46][47][48][49][50], water surface renewal [28,[51][52][53][54][55][56][57], surfactants [28,[58][59][60] and rain [61][62][63][64], just to mention a few examples from an extensive list of published works. In addition to their single influence, these factors also interact.…”

Dielectric and Radiative Properties of Sea Foam at Microwave Frequencies: Conceptual Understanding of Foam Emissivity

“…Whitecap fraction can be evaluated with a number of parameterizations developed for open ocean [8] and coastal zone [9] using photographic measurements [10][11][12] in the visible portion of the electromagnetic (EM) spectrum. Whitecaps can also be observed at infrared [13] and microwave wavelengths [14].…”