Dynamical aspects of shallow sea fronts

1981 ◽  
Vol 302 (1472) ◽  
pp. 563-581 ◽  
Keyword(s):  
Diffusion Equation ◽  
Vertical Mixing ◽  
Circulation Pattern ◽  
Viscosity Coefficient ◽  
Similarity Solutions ◽  
Tidal Mixing ◽  
Interfacial Friction ◽  
Diagnostic Model ◽  
Mean Flow ◽  
The Cross

We examine the role of internal friction in the evolution of a two-dimensional front in a rotating stratified fluid. For a two-layer fluid with interfacial friction the depth of the frontal interface satisfies a diffusion equation with respect to time and the cross-frontal coordinate. Similarity solutions are used to compare the behaviour of the front for linear and quadratic interfacial friction laws. For a continuously stratified front a simple formula is derived for the cross-frontal flow induced by friction, parametrized in terms of an eddy viscosity coefficient Av, provided that the Rossby and Ekman numbers are small. Outside surface and bottom Ekman layers the deptht) of an isopycnal with density p satisfies the diffusion equation z t — [(A 1 2/ / 2) where are the Väisälä and Coriolis frequencies, x is the cross-frontal coordinate and t is time. The consequences of this for the evolution and maintenance of a front are discussed. The circulation in tidal mixing fronts is examined, with results being presented for a semi-analytic diagnostic model, which is fitted to two particular continental shelf fronts. A prominent feature is a two-cell circulation pattern in the plane normal to the front. A variety of cross-frontal transfer mechanisms are discussed, with order-of-magnitude comparisons of their importance being made. Transfer by the mean flow appears to be more important than either shear flow dispersion or the flux associated with baroclinic eddies, but the results are sensitive to the parametrization of vertical mixing of momentum.

scholarly journals Characteristics and Dynamics of Density Fronts over the Inner to Mid-shelf under Weak Wind Conditions

2020 ◽  
Author(s):  
Xiaodong Wu ◽  
Falk Feddersen ◽  
Sarah N. Giddings
Keyword(s):  
Large Scale ◽  
Gravity Current ◽  
Vertical Mixing ◽  
Detection Algorithm ◽  
Mean Flow ◽  
Resolution Model ◽  
High Resolution Model ◽  
The Cross ◽  
Weak Winds ◽  
Light Side

AbstractHere, we explore the kinematics and dynamics of coastal density fronts (within 10 km from shore and < 30 m depth), identified using an edge detection algorithm, in a realistic high resolution model of the San Diego Bight with relatively weak winds and small freshwater input. The density fronts have lengths spanning 4 − 10 km and surface density gradients spanning 2 − 20 × 10−4 kg m−4. Cross-shore oriented fronts are more likely with northward subtidal flow and are 1/3 as numerous as alongshore oriented fronts which are more likely with onshore surface baroclinic diurnal flow. Using a subset of the cross-shore fronts, decomposed into cross-front mean and perturbation components, an ensemble front is created. The ensemble cross-front mean flow is largely geostrophic in the cross- and along-front directions. The ensemble cross-shore front extends several kilometers from shore, with a distinct linear front axis and downwelling (upwelling) on the dense (light) side of the front, convergent perturbation cross-front flow within the upper 5 m, strengthening the ensemble front. Vertical mixing of momentum is weak, counter to the turbulent thermal wind mechanism. The ensemble cross-shore front resembles a gravity current and is generated by a convergent strain field acting on the large scale density field. The ensemble front is bounded by the shoreline and is alongfront geostropic and cross-front ageostrophic. This contrasts with the cross-front geostrophic and along-front ageostrophic balances of classic deformation frontogenesis, but is consistent with semi-geostrophic coastal circulation.

Integral Solution for the Mean Flow Profiles of Turbulent Jets, Plumes, and Wakes

2003 ◽  
Vol 125 (5) ◽  
pp. 813-822 ◽  
Author(s):  
Amit Agrawal ◽  
Ajay K. Prasad
Keyword(s):  
Turbulent Jets ◽  
Universal Constant ◽  
Similarity Solutions ◽  
Stream Velocity ◽  
Centerline Velocity ◽  
Mean Flow ◽  
Production Term ◽  
Entrainment Velocity ◽  
Integral Methods ◽  
The Cross

Integral methods are used to derive similarity solutions for several quantities of interest including the cross-stream velocity, Reynolds stress, the dominant turbulent kinetic energy production term, and eddy diffusivities of momentum and heat for axisymmetric and planar turbulent jets, plumes, and wakes. A universal constant is evaluated for axisymmetric and planar plumes. The cross-stream velocity profiles show that jets and axisymmetric plumes experience an outflow near the axis and an inflow far away from it. The outflow is attributed to the decay of the centerline velocity with downstream distance, and the extent and magnitude of outflow correlates with the streamwise decay of the centerline velocity. It is also shown that the entrainment velocity should not in general be equated to the product of the entrainment coefficient and the centerline velocity. It is found that, due to similar governing equations, profiles for jets and plumes are qualitatively similar. Our results show that the derived quantities are strong functions of streamwise and cross-stream positions, in contrast to previous approaches that assumed constant (in the cross-stream direction) eddy viscosity and thermal diffusivity. The turbulent Prandtl number is approximately equal to unity which matches the value quoted in the literature.

scholarly journals Towards a regional ocean forecasting system for the IBI (Iberia-Biscay-Ireland area): developments and improvements within the ECOOP project framework

Ocean Science ◽  
2012 ◽  
Vol 8 (2) ◽  
pp. 143-159 ◽  
Author(s):  
S. Cailleau ◽  
J. Chanut ◽  
J.-M. Lellouche ◽  
B. Levier ◽  
C. Maraldi ◽  
...  
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Vertical Mixing ◽  
Circulation Model ◽  
Storm Surges ◽  
Ocean General Circulation Model ◽  
Tidal Mixing ◽  
Basin Scale ◽  
Forecasting System ◽  
Ocean Forecasting

Abstract. The regional ocean operational system remains a key element in downscaling from large scale (global or basin scale) systems to coastal ones. It enables the transition between systems in which the resolution and the resolved physics are quite different. Indeed, coastal applications need a system to predict local high frequency events (inferior to the day) such as storm surges, while deep sea applications need a system to predict large scale lower frequency ocean features. In the framework of the ECOOP project, a regional system for the Iberia-Biscay-Ireland area has been upgraded from an existing V0 version to a V2. This paper focuses on the improvements from the V1 system, for which the physics are close to a large scale basin system, to the V2 for which the physics are more adapted to shelf and coastal issues. Strong developments such as higher regional physics resolution in the NEMO Ocean General Circulation Model for tides, non linear free surface and adapted vertical mixing schemes among others have been implemented in the V2 version. Thus, regional thermal fronts due to tidal mixing now appear in the latest version solution and are quite well positioned. Moreover, simulation of the stratification in shelf areas is also improved in the V2.

Linear perturbation response of self-similar ablative flows relevant to inertial confinement fusion

2008 ◽  
Vol 609 ◽  
pp. 1-48 ◽  
Author(s):  
J.-M. CLARISSE ◽  
C. BOUDESOCQUE-DUBOIS ◽  
S. GAUTHIER
Keyword(s):  
Inertial Confinement Fusion ◽  
Similarity Solutions ◽  
Linear Perturbation ◽  
Inertial Confinement ◽  
Mean Flow ◽  
Direct Laser ◽  
Confinement Fusion ◽  
Self Similar ◽  
The Mean ◽  
Compressibility Effects

A family of exact similarity solutions for inviscid compressible ablative flows in slab symmetry with nonlinear heat conduction is proposed for studying unsteadiness and compressibility effects on the hydrodynamic stability of ablation fronts relevant to inertial confinement fusion. Dynamical multi-domain Chebyshev spectral methods are employed for computing both the similarity solution and its time-dependent linear perturbations. This approach has been exploited to analyse the linear stability properties of two self-similar ablative configurations subjected to direct laser illumination asymmetries. Linear perturbation temporal and reduced responses are analysed, evidencing a maximum instability for illumination asymmetries of zero transverse wavenumber as well as three distinct regimes of ablation-front distortion evolution, and emphasizing the importance of the mean flow unsteadiness, compressibility and stratification.

scholarly journals A parameterization of local and remote tidal mixing

2020 ◽  
Author(s):  
Casimir de Lavergne ◽  
Clément Vic ◽  
Gurvan Madec ◽  
Fabien Roquet ◽  
Amy Waterhouse ◽  
...  
Keyword(s):  
Vertical Mixing ◽  
Three Dimensional ◽  
Internal Tide ◽  
Ocean Model ◽  
Internal Tides ◽  
Tidal Mixing ◽  
Global Ocean ◽  
Energy Conserving ◽  
Energy Constrained ◽  
Lagrangian Tracking

&lt;p&gt;Vertical mixing is often regarded as the Achilles&amp;#8217; heel of ocean models. In particular, few models include a comprehensive and energy-constrained parameterization of mixing by internal ocean tides. Here, we present an energy-conserving mixing scheme which accounts for the local breaking of high-mode internal tides and the distant dissipation of low-mode internal tides. The scheme relies on four static two-dimensional maps of internal tide dissipation, constructed using mode-by-mode Lagrangian tracking of energy beams from sources to sinks. Each map is associated with a distinct dissipative process and a corresponding vertical structure. Applied to an observational climatology of stratification, the scheme produces a global three-dimensional map of dissipation which compares well with available microstructure observations and with upper-ocean finestructure mixing estimates. Implemented in the NEMO global ocean model, the scheme improves the representation of deep water-mass transformation and obviates the need for a constant background diffusivity.&lt;/p&gt;

Impact of cross-lapping angle and needling parameters on mechanical and functional properties of nonwoven air filter fabric

2021 ◽  
pp. 152808372110481
Author(s):  
Wondwossen Mamuye ◽  
SM Ishtiaque ◽  
Rupayan Roy ◽  
Priyal Dixit
Keyword(s):  
Fibre Orientation ◽  
Structural Characteristics ◽  
Research Work ◽  
Areal Density ◽  
Nonwoven Fabric ◽  
Mean Flow ◽  
Stroke Frequency ◽  
Air Filter ◽  
Box Behnken Design ◽  
The Cross

This research work investigated the influence of the cross-lapping angle in combination with punch density and stroke frequency on structural characteristics and properties of nonwoven fabric. An attempt has been made to change the cross-lapping angle by keeping the number of layers constant to maintain the same areal density of fabrics. The fibre orientation in the carded web was measured by using Lindsley and image analysis methods. Three variables, that is, cross-lapping angle, punch density and stroke frequency, were considered for the sampling plan to create a three-factor three-level Box–Behnken design. The properties such as mean flow pore size, bursting strength, filtration efficiency and pressure drop were evaluated and analysed in the light of fibre orientation in the carded web. It was concluded that the cross-lapping angle influenced the fibre orientation to a large extent; accordingly, the properties of nonwoven fabric were highly influenced by the fibre orientation.

scholarly journals Relation Between the Interannual Variability in the Stratospheric Rossby Wave Forcing and Zonal Mean Fields Suggesting an Interhemispheric Link in the Stratosphere

2019 ◽  
Author(s):  
Yuki Matsushita ◽  
Daiki Kado ◽  
Masashi Kohma ◽  
Kaoru Sato
Keyword(s):  
Interannual Variability ◽  
Rossby Wave ◽  
Reanalysis Data ◽  
Mean Flow ◽  
Flux Divergence ◽  
Wave Forcing ◽  
Mean Fields ◽  
Meridional Cross Section ◽  
The Cross ◽  
Modern Era

Abstract. Focusing on the interannual variabilities in the zonal mean fields and Rossby wave forcing in austral winter, an interhemispheric coupling in the stratosphere is examined using reanalysis data: the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2). In the present study, the Eliassen-Palm (EP) flux divergence averaged over the latitude and height regions of 50°–30° S and 0.3–1 hPa, respectively, are used as a proxy of the Rossby wave forcing, where the absolute value of the EP flux divergence is maximized in the winter in the Southern Hemisphere (SH). The interannual variabilities in the zonal mean temperature and zonal wind are significantly correlated with the SH Rossby wave forcing in the stratosphere in both the SH and Northern Hemisphere (NH). The interannual variability in the strength of the poleward residual mean flow in the SH stratosphere is also correlated with the strength of the wave forcing. This correlation is significant even around the equator at an altitude of 40 km and at NH low latitudes of 20–40 km. The temperature anomaly is consistent with this residual mean flow anomaly. The relationship between the cross-equatorial flow and the zonal mean absolute angular momentum gradient (My) is examined in the meridional cross section. The My around the equator at the altitude of 40 km is small when the wave forcing is strong, which provides a pathway for the cross-equatorial residual mean flow. These results indicate that an interhemispheric coupling is present in the stratosphere through the meridional circulation modulated by the Rossby wave forcing.

Turbulent Wall-Pressure Fluctuations: A New Model for Off-Axis Cross-Spectral Density

1997 ◽  
Vol 119 (2) ◽  
pp. 277-280 ◽  
Author(s):  
B. A. Singer
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Spectral Density ◽  
Flow Direction ◽  
Wall Pressure ◽  
Mean Flow ◽  
New Approach ◽  
Cross Spectral Density ◽  
The Mean ◽  
The Cross

Models for the distribution of the wall-pressure under a turbulent boundary layer often estimate the coherence of the cross-spectral density in terms of a product of two coherence functions. One such function describes the coherence as a function of separation distance in the mean-flow direction, the other function describes the coherence in the cross-stream direction. Analysis of data from a large-eddy simulation of a turbulent boundary layer reveals that this approximation dramatically underpredicts the coherence for separation directions that are neither aligned with nor perpendicular to the mean-flow direction. These models fail even when the coherence functions in the directions parallel and perpendicular to the mean flow are known exactly. A new approach for combining the parallel and perpendicular coherence functions is presented. The new approach results in vastly improved approximations for the coherence.

scholarly journals Discharge Estimation Using Tsallis and Shannon Entropy Theory in Natural Channels

Water ◽  
2020 ◽  
Vol 12 (6) ◽  
pp. 1786
Author(s):  
Jitendra Kumar Vyas ◽  
Muthiah Perumal ◽  
Tommaso Moramarco
Keyword(s):  
Flow Velocity ◽  
Surface Flow ◽  
Tsallis Entropy ◽  
Accurate Estimation ◽  
Mean Flow ◽  
Flow Area ◽  
Cross Sectional ◽  
The Cross ◽  
Discharge Estimation ◽  
Mean Flow Velocity

Streamflow measurements during high floods is a challenge for which the World Meteorological Organization fosters the development of innovative technologies for achieving an accurate estimation of the discharge. The use of non-contact sensors for monitoring surface flow velocities is of interest to turn these observed values into a cross-sectional mean flow velocity, and subsequently, into discharge if bathymetry is given. In this context, several techniques are available for the estimation of mean flow velocity, starting from observed surface velocities. Among them, the entropy-based methodology for river discharge assessment is often applied by leveraging the theoretical entropic principles of Shannon and Tsallis, both of which link the maximum flow velocity measured at a vertical of the flow area, named the y-axis, and the cross-sectional mean flow velocity at a river site. This study investigates the performance of the two different entropic approaches in estimating the mean flow velocity, starting from the maximum surface flow velocity sampled at the y-axis. A velocity dataset consisting of 70 events of measurements collected at two gauged stations with different geometric and hydraulic characteristics on the Po and Tiber Rivers in Italy was used for the analysis. The comparative evaluation of the velocity distribution observed at the y-axis of all 70 events of measurement was closely reproduced using both the Shannon and Tsallis entropy approaches. Accurate values in terms of the cross-sectional mean flow velocity and discharge were obtained with average errors not exceeding 10%, demonstrating that the Shannon and Tsallis entropy concepts were equally efficient for discharge estimation in any flow conditions.

Tidal Currents and Estuarine-Type Circulation in Johnstone Strait, British Columbia

1976 ◽  
Vol 33 (10) ◽  
pp. 2242-2264 ◽  
Author(s):  
Richard E. Thomson
Keyword(s):  
Lower Layer ◽  
Small Variation ◽  
Tidal Mixing ◽  
Mean Flow ◽  
Western Basin ◽  
Nonlinear Advection ◽  
Tide Height ◽  
The Mean ◽  
Stratified Estuary ◽  
Tidal Signal

Four months of current meter observations across the western basin of Johnstone Strait have been examined, with particular attention given to the mean flow and to variations at tidal frequencies. We show that the time-averaged motions are typical of a moderately stratified estuary driven by tidal mixing and nonlinear advection. Steady currents are nearly unidirectional at all depths with the net outflow in the upper layer essentially balanced by a net inflow in the lower layer to order 103 m3∙s−1. In addition, the relatively small variation in residual current speed is found to decrease with depth and to be associated mostly with the quasi-fortnightly tidal cycle. Near the surface the variance in the residual flow appears to be related to along-channel winds whose speeds and duration exceed 6 m∙s−1 and 24 h, respectively. Time-dependent motions are dominated by the tidal signal which is mixed, predominately semidiurnal. Maximum speeds of order 1 m∙s−1 are found at depth and are generally 1.5–1.7 times larger than in the upper layer. There is also a strong correlation between the tidal current speeds below 150-m depth and the local tide height lagged by 6 h. It is suggested that these large lower layer currents are associated with baroclinic motions being generated by the barotropic tide propagating over the rapidly shoaling bathymetry to the east of the observation region.

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