Gas transfer velocity in the presence of wave breaking

Abstract

A B S T R A C T Wave breaking is known to cause air entrainment and enhancement of the near-surface turbulence. Thus, it intensifies the gas exchange across the airÁsea interface. Based on the combination of the vertical distribution of the turbulence in the wave-affected layer and the breaking wave-energy dissipation rate in the wave-breaking layer, we proposed a composite model for the gas transfer velocity in the presence of wave breaking. The gas transfer velocity was calculated as a function of the air frictional velocity, wave age, and whitecap coverage. The model was validated by the dependences on winds and wave ages by field and laboratory measurements. The results supported the hypothesis that the large uncertainties in the traditional gas transfer velocities based on wind speed alone at moderate-to-high wind speeds can be ascribed to the neglect of the windÁwave effect, which is mainly attributed to the whitecap coverage as a function of the windÁsea Reynolds number.

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

“…Our findings corroborate recent conclusions that the wave state is fundamental for accurate estimates of gas transfer velocities at the fetch-limited coastal ocean [50,57]. Furthermore, our conclusions also agree with Jackson et al [88] and Shuiqing and Dongliang [49] when inferring about the open ocean. In fact, the COAREG (the gas-dedicated version of the COARE) by Jackson et al [88] was applied to data from the GasEx cruises on the Northern Atlantic, Equatorial Pacific and Southern Ocean, with their results also suggesting that the sea state and atmospheric stability are important additional Comparing transfer velocity (k w ) algorithms using modelled data: (Wan92) transfer velocity of CO 2 estimated from Wanninkhof [29] and averaged over the 66 h; (RMSD) Root mean square deviation between estimating the transfer velocity following Wanninkhof [29] or Woolf [44] conjugated with the iterative wind log-linear profile.…”

“…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 .…”

“…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.…”

Turbulence Scaling Comparisons in the Ocean Surface Boundary Layer

“…Compared to T96's parameterization of α on A from Wang and Huang (), we find a different behavior, as we see a consistent decrease for α with A even for A that are below 0.0833. In a similar way, Shuiqing and Dongliang () observed a decrease of α with A and found higher values of α when using their complete data set; when focusing only on young seas with A above 0.0286, α was lower. However, their values of α = 1,700 (full data) and α = 230 (young seas) are still higher than the ones here.…”

“…Our observations support a depth dependency of ϵ described by b = −1.29 above z t , which is less than that proposed by T96 ( b = −2), which was supported by observations in Lake Michigan (Wang & Liao, ), in the Pacific Ocean at depths below approximately one H s (Sutherland & Melville, ), and in the laboratory (Siddiqui & Loewen, ) at depths below 0.4 H s . For measurements in coastal waters of the South China Sea, Shuiqing and Dongliang () find an even more gentle slope with b = −2.11. Feddersen et al () show a slightly smaller decay rate of b = −1.9 in nearshore regions, which still is higher than the b found in the presented study.…”