This paper presents physics improvements to the cool skin parameterization in the Coupled Ocean-Atmosphere Response Experiment (COARE) bulk flux algorithm. The principal improvement is adopting a specification of the ocean side mixing profile that combines molecular and turbulent diffusivities via a form that allows turbulent dissipation to suppress turbulence near the interface. The turbulence is also scaled with the viscous friction velocity, since the stress input to waves is not realized continuously as turbulence at the interface but only intermittently at localized regions where the waves are breaking. Additional improvements include adopting a newer specification of the solar absorption profile in the ocean and incorporating the impacts of the rain sensible heat flux. The new parameterization is tuned to published observations of cool skin from a series of cruises and a recent publication of the turbo-molecular mixing term deduced for observations of gas fluxes. Data from three recent ship-based field programs, particularly the Propagation of Intraseasonal Oscillations in the Maritime Continent Region (PISTON) experiment, with radiometric sea surface and floating near-surface temperature sensors as well as high-quality air-sea flux measurements were analyzed to evaluate the model. The improvements led to modest decreases in the nonsolar cool skin (similar to 16%) and in the solar heating contribution, both principally in light winds. The new model better reproduced mean nighttime cool skin amplitudes and was somewhat better than the previous COARE v3.6 model at reproducing the mean diurnal cycle. Overall, cool skin predictions for a large cruise database were reduced by similar to 0.01 degrees C.

Previous studies of air-sea interactions over sharp oceanic fronts have suggested that it is the ocean that drives the atmosphere across sub-mesoscale ocean fronts, but it is the atmosphere that drives the ocean at synoptic scales; the responsible mechanism, however, is still a matter of debate. This paper examines direct sea surface temperature (SST) measurements of the skin (SST skin) and near-surface SST (SST depth), and wind speeds measured during the Sub-Mesoscale Ocean Dynamics Experiment (S-MODE) along with derived bulk fluxes. We evaluate the modulation of the net heat flux, wind speed, and skin cooling across SST fronts and the ability of the COARE bulk flux algorithm to reproduce this variability. Bulk flux computations can be performed directly from a radiometric SST skin, or more commonly, from the SST depth provided that the depth of the SST measurement is corrected for cool skin and diurnal warming effects. Both types of SST were measured during S-MODE allowing for (a) an assessment of the importance of having a SST skin for a direct flux evaluation in frontal regions, and (b) an evaluation of the accuracy of the cool skin and diurnal warming corrections within COARE for the indirect bulk flux computation. The ocean-atmosphere feedback over the sampled S-MODE submesoscale front suggested that the ocean was indeed forcing the atmosphere, mainly through the surface net heat losses, while the wind response to changes in SST skin was irregular. Testing of the COARE algorithm suggested that indirect bulk fluxes had sufficient accuracy to close the heat budget over the front.

Laboratory experiments were conducted to measure the heat flux from seafoam continuously generated in natural seawater. Using a control volume technique, heat flux was calculated from foam and foam-free surfaces as a function of ambient humidity (ranged from 40% to 78%), air–water temperature difference (ranged from −9 °C to 0 °C), and wind speed (variable up to 3 m s−1). Water-surface skin temperature was imaged with a calibrated thermal infrared camera, and near-surface temperature profiles in the air, water, and foam were recorded. Net heat flux from foam surfaces increased with increasing wind speed and was shown to be up to four times greater than a foam-free surface. The fraction of the total heat flux due to the latent heat flux was observed for foam to be 0.75, with this value being relatively constant with wind speed. In contrast, for a foam-free surface the fraction of the total heat flux due to the latent heat flux decreased at higher wind speeds. Temperature profiles through foam are linear and have larger gradients, which increased with wind speed, while foam free surfaces show the expected logarithmic profile and show no variation with temperature. The radiometric surface temperatures show that foam is cooler and more variable than a foam-free surface, and bubble-resolving thermal images show that radiometrically transparent bubble caps and burst bubbles reveal warm foam below the cool surface layer, contributing to the enhanced variability.

Quantifying energy dissipation due to wave breaking remains an essential but elusive goal for studying and modeling air-sea fluxes of heat, gas, and momentum. Previous observations have shown that lifetimes of bubble plumes and surface foam are directly related to the dissipated energy. Specifically, the foam decay time can be used to estimate the timescale of the subsurface bubble plume and the energy dissipated in the breaking process. A mitigating factor is that the foam decay time can be significantly affected by the surfactant concentration. We present an experimental investigation of a new technique that exploits the thermal signature of cooling foam to infer wave breaking dynamics. The experiments were conducted in a laboratory wave tank using artificial seawater with and without the addition of a surfactant. We show that the time from the start of the breaking process to the onset of cooling scales with the bubble plume decay time and the dissipated energy, and is not significantly affected by the presence of additional surfactants. We confirm observations from the field of the spatial variability of the temperature of foam generated by an individual breaking event, which has implications for inferring the spatial variability of bubble plume depth.

This is the first of a 2-part series concerning remote observation and wave-by-wave analysis of the onset of breaking in the surf zone. In the surf zone, breaking waves drive nearshore circulation, suspend sediment, and promote air-sea gas exchange. Nearshore wave model predictions often diverge from in situ measurements near the break point location because common parameterizations do not account for the rapid changes that occur near the onset of breaking. This work presents extensive methodology to combine data from a line-scanning LIDAR and thermal infrared cameras to detect breaking, classify breaker type, and measure geometric wave parameters on a wave-by-wave basis, which can be used to improve breaker parameterizations. Over 2,600 non-breaking and 1,600 breaking waves are analyzed from data collected at the USACE Field Research Facility in Duck, NC, including 413 spilling and 111 plunging waves for which the onset of breaking was observed. Wave height is estimated using a spatio-temporal method for wave tracking that preserves the sea surface elevation maximum and overcomes field of view limitations. Methods for estimating instantaneous wave speed are refined by fitting a skewed Gaussian function to each wave profile before tracking the peaks. Wave slope is estimated from a linear fit to the upper 80% of the wave face, which provides a robust metric and strong correlation with geometric wave slope defined relative to mean sea level. Finally, breaking wave face foam coverage is analyzed to assess common model assumptions about roller length for wave energy dissipation parameterizations.

Flow in rivers and the coastal ocean is controlled by the frictional force exerted on the water by riverbed or seabed roughness. The frictional force is typically characterized by a drag coefficient Cd, which is estimated from bulk measurements and often assumed constant. Here, we demonstrate a relationship between bed roughness and water surface turbulence that can be used to make remote estimates of Cd. We observe that regions with larger bed roughness result in greater turbulent kinetic energy (TKE), which is transported upward by river boils to the water surface. We present a relationship between surface TKE and Cd, and validate this relationship by comparing remotely sensed estimates of Cd to those from in situ measurements. Thus, our results provide an approach for estimating bottom roughness and Cd based entirely on remotely sensed data, including their spatial variability, which can improve modeling of river discharge and morphodynamics in data‐poor regions.

This is the second of a two-part series concerning remote observation and wave-by-wave analysis of the onset of breaking for spilling and plunging waves in the surf zone. Nearshore phase-averaged and phase-resolving wave models parameterize and directly simulate wave breaking and require realistic critical values of key wave parameters, such as the depth-limited breaking index gamma, steepness, or phase speed to initialize wave breaking. Using LIDAR line-scans and infrared imagery, we observe over 1,600 breaking waves at the US Army Corps of Engineers Field Research Facility (FRF) in Duck, NC, and examine these parameters on a wave-by-wave basis at the onset of breaking for 413 spilling and 111 plunging waves. We find that gamma is maximum near the onset of breaking at values consistent with those previously observed at the FRF, but that gamma for plunging waves (0.73 <= gamma(P) <= 0.81) is greater than gamma for spilling waves (0.63 <= gamma(S) <= 0.71). Direct estimates of wave face slope are maximum at the onset of breaking, approximately 22 degrees for spilling and 30 degrees for plunging waves. Using the relationship between gamma and wave face slope, we develop a threshold for the onset of breaking that is a linear function of the two parameters. Wave face slope and gamma are further used together to quantify whether a spilling- or plunging-type breaker is more likely. We test the Miche steepness limit on our depth-limited breaking data and find it correctly predicts only 10% of the plunging breakers and none of the spilling breakers in the surf zone.

Earth and Space Science Open Archive PosterOpen AccessYou are viewing the latest version by default [v1]Estimating Bubble Plume Dynamics in Breaking Waves using the Thermal Signature of the Residual FoamAuthorsNaeemMasnadiiDC. ChrisChickadelAndrewJessupSee all authors Naeem MasnadiiDCorresponding Author• Submitting AuthorApplied Physics Lab University of WashingtoniDhttps://orcid.org/0000-0003-2697-2230view email addressThe email was not providedcopy email addressC. Chris ChickadelApplied Physics Lab University of Washingtonview email addressThe email was not providedcopy email addressAndrew JessupApplied Physics Lab University of Washingtonview email addressThe email was not providedcopy email address

This study is motivated by the observation that after a wave breaking event in the ocean, the residual surface foam left in the wake of the breaker rapidly cools down. The relationship between the cooling foam and the characteristics of the breaking wave such as bubble plume dynamics, visible surface foam, and energy dissipation is investigated experimentally. Previous studies have suggested that the decay time of the visible foam can be used to determine the dynamics of the subsurface bubble plume and to estimate the energy dissipation by the breaking process but the foam decay process can be greatly affected by the surfactants concentration in the ocean. We present a new approach that utilizes the thermal signature of the cooling foam to infer the breaking characteristics. The experiments are conducted in a wave flume that is equipped with a piston-type wavemaker and is filled with salt water. Breaking …

Sea Surface Temperature (SST) modifies the turbulent mixing, drag, and pressure gradients within the marine atmospheric boundary layer that accelerate near-surface flow from cool to warm SST and decelerate the flow from warm to cool SST. This phenomenon is well documented on scales of 100-1,000 km (the oceanic mesoscale); however, the nature of this air-sea coupling at scales on the order of 1-10 km (the submesoscale) remains unknown. The Advanced Spaceborne Thermal Emission and Reflection Radiometer can be used to study submesoscale phenomena because the high-resolution infrared and near-infrared images can used to estimate both SST and wind speed. Observations of dramatic temperature and wind gradients along the Gulf Stream landward edge are used to examine the surface wind response to submesoscale fronts in SST. Our analysis indicates that SST-induced wind speed perturbations are observed at the scales of order 1-10 km, significantly smaller than previously suggested. Plain Language Summary Seafarers have long known that winds speed up over warm water. The reason for this was not fully understood until the mid-1990 s when satellite observations of sea surface temperature and winds revealed that this phenomenon can be observed in regions where large gradients in sea surface temperature occur. The basic mechanism is quite simple; warm water allows the movement of winds higher up in the atmosphere to be transferred down near the ocean's surface. This is accentuated by a difference in atmospheric pressure over warm and cold water driving a wind from high to low pressure. Using a satellite sensor built to image land, we developed methods to estimate both the sea surface temperature and wind speed at an unprecedented resolution of 100 m, revealing that this phenomenon occurs at spatial scales as small as 1km and over the course of minutes. These observations provide evidence that sea surface temperature induced wind anomalies not only occur at incredibly small scales, in terms of the vastness of the World Ocean, but also that this phenomenon should be included in global atmosphere/ocean simulations if we are to correctly forecast winds over the ocean.

A comprehensive system error source analysis and calibration of an airborne along-track interferometric FMCW SAR for ocean surface currents velocity retrieval is presented. Starting with the observed phase errors from a stationary test site, three major error sources are analyzed and possible calibration approaches are derived. The range-dependent phase offsets are demonstrated to be introduced by the phase imbalance between receive channels and receive antennas of the transceiver. The phase undulations in the along-track direction are likely due to the uncompensated motion errors caused by inaccurate aircraft attitude and velocity measurements. After calibration, most of the system phase errors are removed which greatly improves the accuracy for surface velocity retrieval by ATI-SAR.

During the second Salinity Processes in the Upper-ocean Regional Study (SPURS-2) field experiments in 2016 and 2017 in the eastern tropical Pacific Ocean, the surface salinity profiler (SSP) measured temperature and salinity profiles in the upper 1.1 m of the ocean. The SSP captured the response of the ocean surface to 35 rain events, providing insight into the generation and evolution of rain-formed fresh layers. This paper describes the measurements made with the SSP during SPURS-2 and quantifies the fresh layers in terms of their vertical salinity gradients between 0.05 m and 1.1 m, Delta S1.1-0.05m. For the 35 rain events sampled with the SSP in 2016 and 2017, the maximum value of Delta S1.1-0.05m is well correlated with the accumulated rainfall. The maximum value of Delta S1.1-0.05m is shown to be linearly proportional to the maximum rain rate and inversely proportional to the wind speed. This wind speed-dependent relationship shows a high degree of scatter, reflecting that the vertical salinity gradient formed during any individual rain event depends on the complex interaction between the local ocean dynamics and the highly variable forcing from rain and wind.

Ship-based X-band radar observations of rain were collected with high spatial resolution during the 2016 and 2017 Salinity Processes in the Upperocean Regional Study 2 (SPURS-2) field experiments in the eastern tropical Pacific Ocean. These observations were collected with a repurposed marine radar that is not typically used for weather monitoring. The radar images captured during SPURS-2 show the spatial extent and variable intensity of rain at a horizontal resolution of 180 m within 30 km of the ship. When analyzed alongside collocated measurements of oceanic and atmospheric properties collected during SPURS-2, the radar-derived rain maps enable a clearer understanding of the impact of spatially and temporally varying freshwater fluxes on ocean salinity. Ocean surface freshening, measured by ship gauges, is found to be affected by local rain accumulation, and also by prior rain accumulation in surrounding locations that was measured by radar. In one example, the X-band marine radar measured rain directly ahead of the ship’s path. The ship then sampled a near-surface freshening signature within the time period expected based on the ship speed, ship heading, and rain area measured by the radar. created by rain are referred to here as rain layers. Significant progress has been made in understanding the vertical one-dimensional processes that contribute to rain layer formation and evolution. Using in situ measurements of salinity and temperature and one-dimensional models, Asher et al. (2014), Anderson and Riser (2014), Drushka et al. (2016), and Thompson et al. (2019) demonstrated that the formation of near-surface vertical salinity gradients depends on local rain rate, net heat flux, wind speed, and ocean turbulence. However, according to observations made by You (1995), Thompson et al. (2019), and Drushka et al. (2019), surface freshening and vertical salinity stratification are also often detected when rain is not present locally, but where it rained recently near the location of salinity measurements. In these cases, freshwater deposited on the ocean By Elizabeth J. Thompson, William E. Asher, Andrew T. Jessup, and Kyla Drushka INTRODUCTION Rain often creates density stratification in the upper few meters of the tropical ocean, which can lead to large vertical and horizontal gradients in sea surface salinity (Lukas and Lindstrom, 1991; Anderson et al., 1996; Wijesekera et al., 1999; Anderson and Riser, 2014; Asher et al., 2014; Drushka et al., 2016; Thompson et al., 2019). Following Thompson et al. (2019), stable surface layers in the ocean

Rain-generated lenses of fresher water at the ocean surface affect satellite remote sensing of salinity, mixed-layer dynamics, and air-sea exchange of heat, momentum, and gases.Understanding how rain and wind generate turbulence at the ocean surface is important in modeling the generation and evolution of these fresh lenses.This paper discusses the use of the active controlled flux technique (ACFT) to determine relative levels of turbulence in the top centimeter of the ocean surface in the presence of rain.ACFT measurements were made during the 2016 second Salinity Processes in the Upper-ocean Regional Study (SPURS-2) in the eastern equatorial Pacific Ocean.The data show that at wind speeds below 4 m s -1 , the turbulence dissipation rate at the ocean surface (as parameterized by the water-side surface renewal time constant) is correlated with the instantaneous rain rate.However, at higher wind speeds, the wind stress dominates turbulence production and rain is not a significant source of turbulence.There is also evidence that internal waves can be a significant source of turbulence at the ocean surface under non-raining conditions when a diurnal warm layer is present.

Partnership between the private sector and the ocean observing community brings exciting opportunities to address observing challenges through leveraging the unique strengths of each sector. Here, we discuss a case study of a successful relationship between the National Oceanic and Atmospheric Administration (NOAA) Pacific Marine Environmental Laboratory (PMEL) and Saildrone to instrument an Unmanned Surface Vehicle (USV) in order to serve shared goals. This case study demonstrates that a private company working with a federal laboratory has provided innovative ocean observing solutions deployed at regional scale in only a few years, and we project that this model will be sustainable over the long-term. An alignment of long-term goals with practical deliverables during the development process and integrating group cultures were key to success. To date, this effort has expanded NOAA’s interdisciplinary observing capabilities, improved public access to ocean data, and paved the way for a growing range of USV applications in every ocean. By emphasizing shared needs, complementary strengths, and a clear vision for a sustainable future observing system, we believe that this case study can serve as a blueprint for public and private partners who wish to improve observational capacity. We recommend that the international scientific community continue to foster collaborations between the private sector and regional ocean observing networks. This effort could include regional workshops that build community confidence through independent oversight of data quality. We also recommend that an international framework should be created to organize public and private partners in the atmospheric and oceanographic fields. This body would coordinate development of observational technologies that adhere to best practices and standards for sensor integration, verification, data quality control and delivery, and provide guidance for unmanned vehicle providers. Last, we also recommend building bridges between the private sector, ocean observing community, and the operational forecast community to consider the future of this new private sector, with goals to determine targeted ocean observing needs; assess the appropriateness of USVs as science platforms, sensors, and data format standards; and establish usage and data quality control and distribution protocols for ocean observing and operational forecasting.

Airborne light detection and ranging (LiDAR) measurements and model simulations are used to investigate the temporal and spatial variability of the water surface elevation at the mouth of the Columbia River. A series of 15-km transects repeated in 2-3-h flights over a two week period resolve processes at a range of scales that are important to the dynamics of the river mouth region, including tides, surface slope, surface gravity waves, and wave setup. Water surface elevations agree well with a nearby tide gauge with an average difference of 0.01 m and an root mean square error of 0.39 m. Significant wave heights derived from the LiDAR measurements agree well with in situ wave drifter measurements and are observed to react to both bathymetry and spatial/temporal variations in currents, increasing up to 228 % on large ebb tides. Surface slopes varied from 2.7 x 10(-5) to -2.6 x 10(-5) over the course of a typical tide to as large as 6.3 x 10(-5) to -4.8 x 10(-5) during a larger tide. The magnitude of the setup and set down due to wave height amplification during ebb tide was estimated to be 4 x 10(-6). These observations demonstrate that many of the key dynamical variables at river mouths can be determined from airborne remote sensing measurements of water surface elevation and suggest that forthcoming altimetry products, such as those from the Surface Water Ocean Topography altimeter, may be able to provide new insight on monitoring in these complex regions.

F05. 00003: Inferring Wave Breaking Dissipation Using Cooling Whitecap Foam: A Proof of Concept*