Near-Inertial Waves on the New England Shelf: The Role of Evolving Stratification, Turbulent Dissipation, and Bottom Drag

2005 ◽  
Vol 35 (12) ◽  
pp. 2408-2424 ◽  
Author(s):  
J. A. MacKinnon ◽  
M. C. Gregg
Keyword(s):  
New England ◽  
Internal Waves ◽  
Wind Stress ◽  
Surface Wind ◽  
Inertial Waves ◽  
Transfer Energy ◽  
Turbulent Dissipation ◽  
Bottom Stress ◽  
Surface Warming ◽  
Mode 2

Abstract Energetic variable near-inertial internal waves were observed on the springtime New England shelf as part of the Coastal Mixing and Optics (CMO) project. Surface warming and freshwater advection tripled the average stratification during a 3-week observational period in April/May 1997. The wave field was dominated by near-inertial internal waves generated by passing storms. Wave evolution was controlled by a balance among wind stress, bottom drag, and turbulent dissipation. As the stratification evolved, the vertical structure of these near-inertial waves switched from mode 1 to mode 2 with associated changes in the magnitude and location of wave shear. The growth of mode-2 waves was attributable to a combination of changing wind stress forcing and a nonlinear coupling between the first and second vertical modes through quadratic bottom stress. To explore both forcing mechanisms, an open-ocean mixed layer model is adapted to the continental shelf. In this model, surface wind stress and bottom stress are distributed over the surface and bottom mixed layers and then projected onto orthogonal vertical modes. The model replicates the correct magnitude and evolving modal distribution of the internal waves and confirms that bottom stress can act to transfer energy between internal wave modes.

scholarly journals Spring Mixing: Turbulence and Internal Waves during Restratification on the New England Shelf

2005 ◽  
Vol 35 (12) ◽  
pp. 2425-2443 ◽  
Author(s):  
J. A. MacKinnon ◽  
M. C. Gregg
Keyword(s):  
New England ◽  
Internal Waves ◽  
Mixed Layer ◽  
Wave Interaction ◽  
Heat Fluxes ◽  
Surface Mixed Layer ◽  
Turbulent Dissipation ◽  
Surface Heat Fluxes ◽  
Bottom Boundary Layers ◽  
Diapycnal Diffusivity

Abstract Integrated observations are presented of water property evolution and turbulent microstructure during the spring restratification period of April and May 1997 on the New England continental shelf. Turbulence is shown to be related to surface mixed layer entrainment and shear from low-mode near-inertial internal waves. The largest turbulent diapycnal diffusivity and associated buoyancy fluxes were found at the bottom of an actively entraining and highly variable wind-driven surface mixed layer. Away from surface and bottom boundary layers, turbulence was systematically correlated with internal wave shear, though the nature of that relationship underwent a regime shift as the stratification strengthened. During the first week, while stratification was weak, the largest turbulent dissipation away from boundaries was coincident with shear from mode-1 near-inertial waves generated by passing storms. Wave-induced Richardson numbers well below 0.25 and density overturning scales of several meters were observed. Turbulent dissipation rates in the region of peak shear were consistent in magnitude with several dimensional scalings. The associated average diapycnal diffusivity exceeded 10−3 m2 s−1. As stratification tripled, Richardson numbers from low-mode internal waves were no longer critical, though turbulence was still consistently elevated in patches of wave shear. Kinematically, dissipation during this period was consistent with the turbulence parameterization proposed by MacKinnon and Gregg, based on a reinterpretation of wave–wave interaction theory. The observed growth of temperature gradients was, in turn, consistent with a simple one-dimensional model that vertically distributed surface heat fluxes commensurate with calculated turbulent diffusivities.

The temporal variability of near-inertial internal waves in an internal tide beam

2021 ◽  
Author(s):  
Jonas Löb ◽  
Monika Rhein
Keyword(s):  
Internal Wave ◽  
Internal Waves ◽  
Temporal Variability ◽  
Internal Tide ◽  
Internal Tides ◽  
Inertial Waves ◽  
Energy Fluxes ◽  
Wind Event ◽  
Mode 2 ◽  
Inertial Energy

<p>Low mode internal waves in the stratified ocean are generated by the interaction between barotropic tides and seafloor topography and by the wind field in the near-inertial range. They are crucial for interior mixing and for the oceanic energy pathways, since they carry a large portion of the energy of the entire internal wave field. Long-term observations of energy fluxes of internal waves are sparse. The aim of this work is to study the temporal variability of wind generated low mode near-inertial internal waves inside an internal tide beam emanating from seamounts south of the Azores. For this, 20 months of consecutive mooring observations are used to calculate the mode 1 and mode 2 near-inertial energy fluxes as well as kinetic and potential energies. The gathered time series of near-inertial internal wave energy flux is not steady due to its intermittent forcing and is neither dominated by either mode 1 or mode 2. It shows a peak induced by a distinct strong wind event which is directly linked to wind-power input into the mixed layer north-east of the mooring location, and allows a comparison between the wind event and a background state. Furthermore, indications of non-linear interactions of the near-inertial waves with the internal tides in the form of resonant triad interaction and non-linear self-interaction have been found. This study provides new insights on the relative importance of single wind events and reinforces the assumption of a global non-uniform distribution of near-inertial energy with emphasis in regions where these events occur often and regularly. It furthermore displays its importance to be adequately incorporated into ocean general circulation models and in generating ocean mixing estimates by near-inertial waves as a similarly important component next to the internal tides.</p>

scholarly journals The evolution of mode-2 nonlinear internal waves over the northern Heng-Chun Ridge south of Taiwan

2015 ◽  
Vol 22 (4) ◽  
pp. 413-431 ◽  
Author(s):  
S. R. Ramp ◽  
Y. J. Yang ◽  
D. B. Reeder ◽  
M. C. Buijsman ◽  
F. L. Bahr
Keyword(s):  
Internal Waves ◽  
High Frequency ◽  
Velocity Structure ◽  
Primary Study ◽  
Turbulent Dissipation ◽  
Nonlinear Internal Waves ◽  
Mode 2 ◽  
Sill Depth ◽  
The Waves ◽  
Very High

Abstract. Two research cruises were conducted from the R/V OCEAN RESEARCHER 3 during 05–16 August 2011 to study the generation and propagation of high-frequency nonlinear internal waves (NLIWs) over the northern Heng-Chun Ridge south of Taiwan. The primary study site was on top of a smaller ridge about 15 km wide by 400 m high atop the primary ridge, with a sill depth of approximately 600 m. A single mooring was used in conjunction with shipboard observations to sample the temperature, salinity and velocity structure over the ridge. All the sensors observed a profusion of mode-2 NLIWs. Some of the waves were solitary, while others had as many as seven evenly spaced waves per packet. The waves all exhibited classic mode-2 velocity structure with a core near 150–200 m and opposing velocities in the layers above and below. At least two and possibly three most common propagation directions emerged from the analysis, suggesting multiple generation sites near the eastern side of the ridge. The turbulent dissipation due to overturns in the wave cores was very high at order 10−4–10−3 W kg−1. The energy budget suggests that the waves cannot persist very far from the ridge and likely do not contribute to the South China Sea transbasin wave phenomenon.

scholarly journals The evolution of Mode-2 nonlinear internal waves over the northern Heng-Chun ridge south of Taiwan

2015 ◽  
Vol 2 (1) ◽  
pp. 243-296 ◽  
Author(s):  
S. R. Ramp ◽  
Y. J. Yang ◽  
D. B. Reeder ◽  
M. C. Buijsman ◽  
F. L. Bahr
Keyword(s):  
Internal Waves ◽  
High Frequency ◽  
Velocity Structure ◽  
Primary Study ◽  
Turbulent Dissipation ◽  
Nonlinear Internal Waves ◽  
Mode 2 ◽  
Sill Depth ◽  
The Waves ◽  
Very High

Abstract. Two research cruises were conducted from the R/V OCEAN RESEARCHER 3 during 5–16 August 2011 to study the generation of high-frequency nonlinear internal waves (NLIW) over the northern Heng-Chun Ridge south of Taiwan. The primary study site, centered near 21°34' N, 120°54' E, was on top of a smaller ridge about 15 km wide by 400 m high atop the primary ridge, with a sill depth of approximately 600 m. The bottom slope was steep over both sides of the ridge, supercritical with respect to both diurnal and semidiurnal tides. The key result of the experiments is that a profusion of mode-2 NLIW were observed by all the sensors. Some of the waves were solitary while others had as many as seven evenly-spaced waves per packet. The waves all exhibited classic mode-2 velocity structure with a core near 150–200 m and opposing velocities in the layers above and below. At least two and possibly three most common propagation directions emerged from the analysis, suggesting multiple generation sites near the east side of the ridge. The turbulent dissipation due to overturns in the wave cores was very high at order 10−4–10−3 W kg−1. The energy budget suggests that the waves cannot persist very far from the ridge and likely do not contribute to the South China Sea transbasin wave phenomenon.

scholarly journals Observations of nonlinear momentum fluxes over the inner continental shelf

2021 ◽  
Vol 79 (1) ◽  
pp. 27-66
Author(s):  
Thomas P. Connolly ◽  
Steven J. Lentz
Keyword(s):  
Continental Shelf ◽  
New England ◽  
Wind Stress ◽  
Vertical Shear ◽  
Momentum Balance ◽  
Inner Shelf ◽  
Bottom Stress ◽  
Momentum Fluxes ◽  
Inner Continental Shelf

Nonlinear momentum fluxes over the inner continental shelf are examined using moored observations from multiple years at two different locations in the Middle Atlantic Bight. Inner shelf dynamics are often described in terms of a linear alongshore momentum balance, dominated by frictional stresses generated at the surface and bottom. In this study, observations over the North Carolina inner shelf show that the divergence of the cross-shelf flux of alongshore momentum is often substantial relative to the wind stress during periods of strong stratification. During upwelling at this location, offshore fluxes of alongshore momentum in the surface layer partially balance the wind stress and reduce the role of the bottom stress. During downwelling, onshore fluxes of alongshore momentum reinforce the wind stress and increase the role of bottom stress. Over the New England inner shelf, nonlinear terms have less of an impact in the momentum balance and exhibit different relationships with the wind forcing. Differences between locations and time periods are explained by variations in bottom slope, latitude, vertical shear and cross-shelf exchange. Over the New England inner shelf, where moored density data are available, variations in vertical shear are explained by a combination of thermal wind balance and wind stress. An implication of this study is that cross-shelf winds can potentially influence the alongshore momentum balance over the inner shelf, in contrast with deeper locations over the middle to outer shelf.

FEATURES OF WIND FIELD OVER THE SEA SURFACE IN THE COASTAL AREA BASED ON SAR OBSERVATIONS

2017 ◽  
Author(s):  
Anna Monzikova ◽  
Anna Monzikova ◽  
Vladimir Kudryavtsev Vladimir ◽  
Vladimir Kudryavtsev Vladimir ◽  
Alexander Myasoedov ◽  
...  
Keyword(s):  
Wind Stress ◽  
Surface Wind ◽  
Quantitative Description ◽  
Energy Resource ◽  
Resource Assessment ◽  
Internal Boundary Layer ◽  
Offshore Wind ◽  
Internal Boundary ◽  
Sar Images ◽  
Surface Wind Stress

“Wind-shadowing” effects in the Gulf of Finland coastal zone are analyzed using high resolution Envisat Synthetic Aperture Radar (SAR) measurements and model simulations. These effects are related to the internal boundary layer (IBL) development due to abrupt change the surface roughness at the sea-land boundary. Inside the "shadow" areas the airflow accelerates and the surface wind stress increases with the fetch. Such features can be revealed in SAR images as dark areas adjacent to the coastal line. Quantitative description of these effects is important for offshore wind energy resource assessment. It is found that the surface wind stress scaled by its equilibrium value (far from the coast) is universal functions of the dimensionless fetch Xf/G. Wind stress reaches an equilibrium value at the distance Xf/G of about 0.4.

scholarly journals Influence of El Niño Wind Stress Anomalies on South Brazil Bight Ocean Volume Transports

2015 ◽  
Vol 2015 ◽  
pp. 1-15 ◽  
Author(s):  
Luiz Paulo de Freitas Assad ◽  
Carina Stefoni Böck ◽  
Rogerio Neder Candella ◽  
Luiz Landau
Keyword(s):  
Stress Field ◽  
Interannual Variability ◽  
Wind Stress ◽  
Large Scale ◽  
Time Lag ◽  
Surface Wind ◽  
Circulation Model ◽  
Volume Transport ◽  
Wind Stress Field ◽  
Volume Transports

The knowledge of wind stress variability could represent an important contribution to understand the variability over upper layer ocean volume transports. The South Brazilian Bight (SBB) circulation had been studied by numerous researchers who predominantly attempted to estimate its meridional volume transport. The main objective and contribution of this study is to identify and quantify possible interannual variability in the ocean volume transport in the SBB induced by the sea surface wind stress field. A low resolution ocean global circulation model was implemented to investigate the volume transport variability. The results obtained indicate the occurrence of interannual variability in meridional ocean volume transports along three different zonal sections. These results also indicate the influence of a wind driven large-scale atmospheric process that alters locally the SBB and near-offshore region wind stress field and consequently causes interannual variability in the upper layer ocean volume transports. A strengthening of the southward flow in 25°S and 30°S was observed. The deep layer ocean volume transport in the three monitored sections indicates a potential dominance of other remote ocean processes. A small time lag between the integrated meridional volume transports changes in each monitored zonal section was observed.

Wind Stress Over Waves: Effects of Sea Roughness and Atmospheric Stability

2002 ◽  
Vol 124 (3) ◽  
pp. 169-172 ◽  
Author(s):  
Dag Myrhaug ◽  
Olav H. Slaattelid
Keyword(s):  
Boundary Layer ◽  
Wind Stress ◽  
Local Equilibrium ◽  
Surface Wind ◽  
Atmospheric Stability ◽  
Sea Surface ◽  
Stability Function ◽  
Sea Surface Wind ◽  
Surface Wind Stress ◽  
Sea Surface Roughness

The paper considers the effects of sea roughness and atmospheric stability on the sea surface wind stress over waves, which are in local equilibrium with the wind, by using the logarithmic boundary layer profile including a stability function, as well as adopting some commonly used sea surface roughness formulations. The engineering relevance of the results is also discussed.

Reduced Stability of the Atlantic Meridional Overturning Circulation due to Wind Stress Feedback during Glacial Times

2008 ◽  
Vol 21 (23) ◽  
pp. 6260-6282 ◽  
Author(s):  
Olivier Arzel ◽  
Matthew H. England ◽  
Willem P. Sijp
Keyword(s):  
Sea Ice ◽  
Wind Stress ◽  
Surface Wind ◽  
Meridional Overturning Circulation ◽  
Nonlinear Dependence ◽  
Upper Ocean ◽  
Overturning Circulation ◽  
Climate Conditions ◽  
Meridional Overturning ◽  
The Impact

Abstract A previous study by Mikolajewicz suggested that the wind stress feedback stabilizes the Atlantic thermohaline circulation. This result was obtained under modern climate conditions, for which the presence of the massive continental ice sheets characteristic of glacial times is missing. Here a coupled ocean–atmosphere–sea ice model of intermediate complexity, set up in an idealized spherical sector geometry of the Atlantic basin, is used to show that, under glacial climate conditions, wind stress feedback actually reduces the stability of the meridional overturning circulation (MOC). The analysis reveals that the influence of the wind stress feedback on the glacial MOC response to an external source of freshwater applied at high northern latitudes is controlled by the following two distinct processes: 1) the interactions between the wind field and the sea ice export in the Northern Hemisphere (NH), and 2) the northward Ekman transport in the tropics and upward Ekman pumping in the core of the NH subpolar gyre. The former dominates the response of the coupled system; it delays the recovery of the MOC, and in some cases even stabilizes collapsed MOC states achieved during the hosing period. The latter plays a minor role and mitigates the impact of the former process by reducing the upper-ocean freshening in deep-water formation regions. Hence, the wind stress feedback delays the recovery of the glacial MOC, which is the opposite of what occurs under modern climate conditions. Close to the critical transition threshold beyond which the circulation collapses, the glacial MOC appears to be very sensitive to changes in surface wind stress forcing and exhibits, in the aftermath of the freshwater pulse, a nonlinear dependence upon the wind stress feedback magnitude: a complete and irreversible MOC shutdown occurs only for intermediate wind stress feedback magnitudes. This behavior results from the competitive effects of processes 1 and 2 on the midlatitude upper-ocean salinity during the shutdown phase of the MOC. The mechanisms presented here may be relevant to the large meltwater pulses that punctuated the last glacial period.

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