Observations of Air‐Sea Momentum Flux Variability Across the Inner Shelf

Ortiz‐Suslow, David G.; Haus, Brian K.; Williams, Neil J.; Graber, Hans C.; MacMahan, Jamie

doi:10.1029/2018jc014348

Cited by 15 publications

(20 citation statements)

References 52 publications

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“…During CASPER‐West, the sea state was persistently mixed, with three directionally distinct energy bands identifiable throughout much of the experiment: E s , E m , and E w , where E is the surface elevation variance density and subscripts represent the low frequency swell ( s ), mid‐frequency swell ( m ), and local windsea bands ( w ), respectively. The three bands were separated by f s (an arbitrary limit between E s and E m set to 0.08333) and f c , defined as (Ortiz‐Suslow et al., 2018):

f_{c} = \frac{g}{2.4 π U c o s (ψ - D_{p})},

where g is gravitational acceleration (9.81 ms −1 ), U is the local mean wind speed, ψ is the local mean wind direction, and D p is the direction of the spectral wave peak. If f c < 0.125, then the sea state was assumed to resemble a bi‐modal distribution with distinct swell ( E s ) and windsea ( E w ) bands only, that is, E m = 0.…”

Section: Methodology and Approachmentioning

confidence: 99%

“…Several field studies have shown that the relative direction between the wind and dominant waves can help explain unexpected changes in wind stress and other parameters with time and/or space (Grachev et al 2003;Ortiz-Suslow et al 2018, 2015Shabani et al 2014;Zhang, Drennan, Haus, & Graber 2009). To account for this here, the relative angle between the wind direction (ψ) and mid-frequency swell peak wave directions (D pm ) was examined.…”

Section: Definition Of Surface Wave Spectral Energy Bandsmentioning

confidence: 99%

“…During CASPER-West, the sea state was persistently mixed, with three directionally distinct energy bands identifi- able throughout much of the experiment: E s , E m , and E w , where E is the surface elevation variance density and subscripts represent the low frequency swell (s), mid-frequency swell (m), and local windsea bands (w), respectively. The three bands were separated by f s (an arbitrary limit between E s and E m set to 0.08333) and f c , defined as (Ortiz-Suslow et al, 2018):…”

Section: Definition Of Surface Wave Spectral Energy Bandsmentioning

confidence: 99%

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An Evaluation of the Constant Flux Layer in the Atmospheric Flow Above the Wavy Air‐Sea Interface

et al. 2021

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f_{c} = \frac{g}{2.4 π U c o s (ψ - D_{p})},

Section: Methodology and Approachmentioning

confidence: 99%

Section: Definition Of Surface Wave Spectral Energy Bandsmentioning

confidence: 99%

Section: Definition Of Surface Wave Spectral Energy Bandsmentioning

confidence: 99%

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An Evaluation of the Constant Flux Layer in the Atmospheric Flow Above the Wavy Air‐Sea Interface

et al. 2021

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“…However, COARE does not isolate the contribution or impact of SF to the fluxes, and therefore doing a comparison between EC and bulk techniques may highlight the separate impact SF have on the air‐sea exchange. This method of testing against bulk parameterizations has been used to assess the impact of nonresolved processes in previous works, for example, over complex nearshore regions (Ortiz‐Suslow et al, , ).…”

Section: Analysis Methodsmentioning

confidence: 99%

The Variability of Winds and Fluxes Observed Near Submesoscale Fronts

et al. 2019

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Submesoscale oceanic fronts (SFs), which typically occur on a spatial scale of 0.1-10 km, may have a large influence on the atmospheric surface layer (ASL). However, due to their short temporal-spatial scales, evaluating their direct impact on this layer remains challenging and characterizing the nature of SF-ASL interaction has not been done in the field. To address this, a study of the air-sea response to SFs was conducted using observations collected during the Lagrangian Submesoscale Experiment, which took place in the northern Gulf of Mexico. This manuscript focuses on the meteorological measurements made from a pair of masts installed on the bow of the R/V Walton Smith. This work represents one of the first observation-based investigations into the potential influence that SFs have on the ASL. Contemporaneous measurements from an X-band marine radar, moving vessel profiler, and Lagrangian drifters were also used to analyze the SF dynamics. Systematic surface wind velocity changes over several cross-frontal transects were observed, a process previously associated with mesoscale fronts. A comparison between the eddy covariance and parameterized (COARE 3.5) air-sea fluxes revealed that the directly observed heat flux was 1.5 times larger than the bulk value in the vicinity of the SFs. This suggests that the hydrodynamic processes near the front enhance the local exchange of sensible and latent heat. Given the prevalence of SF over the global upper ocean, these findings suggest that these features may have a widely distributed and cumulative impact on air-sea interactions. Plain Language SummaryThe atmosphere responds to the ocean over all scales-from microscopic to planetary scales. Previous studies showed that surface wind and even the entire atmospheric boundary layer could be affected by the relatively large-scale (10-1,000 km) temperature variations across the open ocean, for example, the Gulf Stream. However, the impacts of relatively small-scale (100 m to 10 km) and rapidly (hours to days) evolving fronts are largely unknown due to the difficulty in actually observing the physical processes. As part of an ongoing effort to better understand surface material dispersion across the northern Gulf of Mexico, we conducted ship-based measurements of air-sea fluxes across near small-scale fronts. The observations showed that the physical mechanism used to explain the interaction between the atmosphere and large-scale ocean temperature gradients readily downscales to these smaller fronts, which have a direct impact of wind directly above the ocean surface. These small-scale fronts were also observed to locally enhance the air-sea heat flux, and the conventional model used to predict this underestimates the observed value by as much as 50%. These small-scale frontal features are common across the global ocean, and our findings suggest that they could cumulatively impact the global energy budget.

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“…They further observed the stress vector deviation to be correlated with the horizontal current shear, and concluded that open ocean parameterizations underestimate the drag coefficient by a factor of 2.6. Recently, Ortiz-Suslow et al [10] observed a shift from swell-to current-dominated wind stress veering at a distance of 2 km off the coast in Monterey Bay, California. They reported a relationship between the wind stress veering and the alongshore surface current variance, within 2 km off the coast.…”

Section: Introductionmentioning

confidence: 99%

Wind Stress in the Coastal Zone: Observations from a Buoy in Southwestern Norway

et al. 2019

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Several studies have focused on the investigation of the wind stress in open ocean conditions where coastal processes were negligible. However, the direction and magnitude of the wind stress vector in coastal areas are still not fully known due to the low number of available measurement datasets. Here, we present new observations of the wind stress magnitude and its deviation from the mean wind direction. The data were recorded from a surface buoy during a five-day measurement campaign in southwestern Norway and cover wind speeds up to 10 m s−1 and significant wave heights up to 3.5 m in a coastal area with a steeply sloping sea floor. The adjustment of the wind stress vector due to changes in the wind and the wave conditions is illustrated and discussed by means of seven sample cases associated with both wind-following swell, cross-swell and counter-swell conditions. For this purpose, the stress vector computed in the sonic anemometer’s orthogonal coordinate system is projected into a non-orthogonal wind-swell coordinate system with its components aligned with: (1) the local wind-generated waves propagating in the wind direction; and (2) the swell wave direction. The wind stress direction was found to deviate from the wind direction by more than 20° for 46% of the recorded wind-following swell and cross-swell cases and for 54% of the counter-swell cases. The wind stress magnitude was observed to approach zero during the counter-swell period, which suggest a decoupling between the sea surface and the atmospheric surface layer. This was further investigated by means of an idealized Large Eddy Simulation results. The results in this study provide additional experimental evidence that the wind stress direction in coastal areas with a steeply sloping sea floor is influenced by the swell waves, the wave age and the wave steepness when the wind blows from undisturbed open ocean directions. For landward wind directions, the influence of the land boundary layer can, possibly in combination with atmospheric stability, adjust the magnitude and direction of the wind stress.

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Observations of Air‐Sea Momentum Flux Variability Across the Inner Shelf

Cited by 15 publications

References 52 publications

An Evaluation of the Constant Flux Layer in the Atmospheric Flow Above the Wavy Air‐Sea Interface

An Evaluation of the Constant Flux Layer in the Atmospheric Flow Above the Wavy Air‐Sea Interface

The Variability of Winds and Fluxes Observed Near Submesoscale Fronts

Wind Stress in the Coastal Zone: Observations from a Buoy in Southwestern Norway

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