Observations from a suite of platforms deployed in the coastal ocean are being combined with numerical models and simulations to investigate the processes that couple the atmosphere and ocean.

Abstract. Laboratory results showing that the air-water gas transfer velocity k is correlated with mean square wave slope have been cited as evidence that a wave-related mechanism regulates k at low to moderate wind speeds [JShne et al., 1987;Bock et al., 1999]. Csanady [1990] has modeled the effect of microscale wave breaking on air-water gas transfer with the result that k is proportional to the fractional surface area covered by surface renewal generated during the breaking process. In this report we investigate the role of microscale wave breaking in gas transfer by determining the correlation between k and AB, the fractional area coverage of microscale breaking waves. Simultaneous, colocated infrared (IR) and wave slope imagery is used to verify that AB detected using IR techniques corresponds to the fraction of surface area covered by surface renewal in the wakes of microscale breaking waves. Using measurements of k and AB made at the University of Washington wind-wave tank at wind speeds from 4.6 to 10.7 m s -1, we show that k is linearly correlated with AB, regardless of the presence of surfactants. This result is consistent with Csanady's [1990] model and implies that microscale wave breaking is likely a fundamental physical mechanism contributing to gas transfer.

[1] The role of microscale wave breaking in controlling the air-water transfer of heat and gas is investigated in a laboratory wind-wave tank. The local heat transfer velocity, k H , is measured using an active infrared technique and the tank-averaged gas transfer velocity, k G , is measured using conservative mass balances. Simultaneous, colocated infrared and wave slope imagery show that wave-related areas of thermal boundary layer disruption and renewal are the turbulent wakes of microscale breaking waves, or microbreakers. The fractional area coverage of microbreakers, A B , is found to be 0.1-0.4 in the wind speed range 4.2-9.3 m s À1 for cleaned and surfactant-influenced surfaces, and k H and k G are correlated with A B . The correlation of k H with A B is independent of fetch and the presence of surfactants, while that for k G with A B depends on surfactants. Additionally, A B is correlated with the mean square wave slope, hS 2 i, which has shown promise as a correlate for k G in previous studies. The ratio of k H measured inside and outside the microbreaker wakes is 3.4, demonstrating that at these wind speeds, up to 75% of the transfer is the direct result of microbreaking. These results provide quantitative evidence that microbreaking is the dominant mechanism contributing to air-water heat and gas transfer at low to moderate wind speeds.

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Vertical salinity gradients in the top few meters of the ocean surface can exist due to the freshwater input from rain. If present, surface gradients complicate comparing salinity measured at depths of a few meters to salinities retrieved using L-band microwave radiometers such as SMOS and Aquarius. Therefore, understanding the spatial scales and the frequency of occurrence of these vertical gradients and the conditions under which they form will be important in understanding sea surface salinity maps provided by microwave radiometers. Salinity gradients in the near-surface ocean were measured using a towed profiler that profiled salinity in the top 2 m of the ocean with a minimum measurement depth of 0.1 m. In addition, an Underway Salinity Profiling System was installed on the R/V Thomas G. Thompson. This measured nearsurface salinity at depths of 1 and 2 m. Both the towed profiler and the underway system found the occurrence of negative salinity anomalies (i.e., salinity decreasing toward the surface) was correlated with the presence of rain. The magnitude of the anomaly (i.e., the difference between salinity at 0.1 m and the salinity at 0.26 m) was proportional to the cube of the rain rate for rain rate, R, greater than 6 mm h 21 . From this, for R > 15-22 mm h 21 , depending on the areal extent of the salinity anomalies, rain can cause sceneaveraged salinity offsets that are as large as the accuracy goal for Aquarius of 0.1&.

[1] Energy dissipation by breaking water waves is quantified indirectly using remote observations (digital video recordings) and directly using in situ observations (acoustic Doppler velocity profiles). The analysis is the first validation using field data to test the Duncan-Phillips formulation relating energy dissipation to the spectral distribution of whitecap speeds and lengths. Energy dissipation estimates are in agreement over two orders of magnitude, and demonstrate a promising method for routine observation of wave breaking dynamics. Breaking statistics are partitioned into contributions from waves at the peak of the wave-height spectrum and waves at higher frequencies in the spectrum. Peak waves are found to be only 10% of the total breaking rate, however peak waves contribute up to 75% of the total dissipation rate. In addition, breaking statistics are found to depend on the peak wave steepness and the energy input by the wind. Citation: Thomson, J., J. R.Gemmrich, and A. T. Jessup (2009), Energy dissipation and the spectral distribution of whitecaps, Geophys. Res. Lett., 36, L11601,

Abstract. Breaking without air entrainment of very short wind-forced waves, or microscale wave breaking, is undoubtedly widespread over the oceans and may prove to be a significant mechanism for enhancing the transfer of heat and gas across the air-sea interface. However, quantifying the effects of microscale wave breaking has been difficult because the phenomenon lacks the visible manifestation of whitecapping. In this brief report we present limited but promising laboratory measurements which show that microscale wave breaking associated with evolving wind waves disturbs the thermal boundary layer at the air-water interface, producing signatures that can be detected with infrared imagery. Simultaneous video and infrared observations show that the infrared signature itself may serve as a practical means of defining and characterizing the microscale breaking process. The infrared imagery is used to quantify microscale breaking waves in terms of the frequency of occurrence and the areal coverage, which is substantial under the moderate wind speed conditions investigated. The results imply that "bursting" phenomena observed beneath laboratory wind waves are likely produced by microscale breaking waves but that not all microscale breaking waves produce bursts. Oceanic measurements show the ability to quantify microscale wave breaking in the field. Our results demonstrate that infrared techniques can provide the information necessary to quantify the breaking process for inclusion in models of air-sea heat and gas fluxes, as well as unprecedented details on the origin and evolution of microscale wave breaking.

We report the results from a laboratory investigation in which microscale breaking waves were detected using an infrared (IR) imager and two-dimensional (2-D) velocity fields were simultaneously measured using particle image velocimetry (PIV). In addition, the local heat transfer velocity was measured using the controlled flux technique. To the best of our knowledge these are the first measurements of the instantaneous 2-D velocity fields generated beneath microscale breaking waves. Careful measurements of the water surface profile enabled us to make accurate estimates of the near-surface velocities using PIV. Previous experiments have shown that behind the leading edge of a microscale breaker the cool skin layer is disrupted creating a thermal signature in the IR image [Jessup et al., J. Geophys. Res. 102, 23145 (1997)]. The simultaneously sampled IR images and PIV data enabled us to show that these disruptions or wakes are typically produced by a series of vortices that form behind the leading edge of the breaker. When the vortices are first formed they are very strong and coherent but as time passes, and they move from the crest region to the back face of the wave, they become weaker and less coherent. The near-surface vorticity was correlated with both the fractional area coverage of microscale breaking waves and the local heat transfer velocity. The strong correlations provide convincing evidence that the wakes produced by microscale breaking waves are regions of high near-surface vorticity that are in turn responsible for enhancing air–water heat transfer rates.