scholarly journals Reply to “Comment on ‘Abyssal Upwelling and Downwelling Driven by Near-Boundary Mixing’”

2018 ◽  
Vol 48 (3) ◽  
pp. 749-753 ◽  
Author(s):  
Trevor J. McDougall ◽  
Raffaele Ferrari
Keyword(s):  
Control Volume ◽  
Buoyancy Flux ◽  
Horizontal Distance ◽  
Simple Assumption ◽  
Boundary Mixing ◽  
Topographic Features ◽  
Budget Analysis ◽  
Abyssal Mixing ◽  
And Diffusion ◽  
Upwelling And Downwelling

AbstractLedwell, in a comment on McDougall and Ferrari, discusses the dianeutral upwelling and downwelling that occurs near isolated topographic features, by performing a buoyancy budget analysis that integrates the diffusive buoyancy fluxes only out to a set horizontal distance from the topography. The consequence of this choice of control volume is that the magnitude of the area-integrated diffusive buoyancy flux decreases to zero at the base of a topographic feature resulting in a net dianeutral upwelling of water. Based on this result, Ledwell argues that isolated topographic features are preferential locations for the upwelling of waters from the abyss. However the assumptions behind Ledwell’s analysis may or may not be typical of abyssal mixing in the ocean. McDougall and Ferrari developed general expressions for the balance between area-integrated dianeutral advection and diffusion, and then illustrated these general expressions using the very simple assumption that the magnitude of the buoyancy flux per unit area at the top of the turbulent boundary layer was constant. In these pedagogical illustrations, McDougall and Ferrari concentrated on the region near the top (rather than near the base) of isolated topographic features, and they found net sinking of abyssal waters. Here we show that McDougall and Ferrari’s conclusion that isolated topographic features cause dianeutral downwelling is in fact a result that applies for general geometries and for all forms of bottom-intensified mixing profiles at heights above the base of such topographic features.

scholarly journals BUOYANCY SPREAD OF WASTE WATER IN COASTAL REGIONS

1968 ◽  
Vol 1 (11) ◽  
pp. 89 ◽  
Author(s):  
Ian Larsen ◽  
Torben Sorenson
Keyword(s):  
Waste Water ◽  
Practical Importance ◽  
Cooling Water ◽  
Buoyancy Flux ◽  
Coastal Regions ◽  
Great Practical Importance ◽  
And Diffusion

Waste water may due to buoyancy effects spread horizontally on top of the recipient. The spreading is chiefly determined by the buoyancy flux and to a large extent unaffected by dilution and diffusion. This phenomenon is of great practical importance for larger outfalls of waste or cooling water in coastal regions.

Snow and blue-ice distribution patterns on the coastal Antarctic Ice Sheet

2000 ◽  
Vol 12 (1) ◽  
pp. 69-79 ◽  
Author(s):  
Glen E. Liston ◽  
Jan-Gunnar Winther ◽  
Oddbjørn Bruland ◽  
Hallgeir Elvehøy ◽  
Knut Sand ◽  
...  
Keyword(s):  
Transport Model ◽  
Distribution Patterns ◽  
Snow Accumulation ◽  
Horizontal Distance ◽  
Topographic Features ◽  
Dronning Maud Land ◽  
Screen Height ◽  
Topography Model ◽  
Surface Patterns ◽  
Snow Transport

Surface patterns of alternating snow and blue-ice bands are found in the Jutulgryta area of Dronning Maud Land, Antarctica. The snow-accumulation regions exist in the lee of blue-ice topographic ridges aligned perpendicular to winter winds. The snow bands are c. 500–2000 m wide and up to several kilometres long. In Jutulgryta, these features cover c. 5000 km2. These alternating snow and blue-ice bands are simulated using a snow transport and redistribution model, SnowTran-3D, that is driven with a winter cycle of observed daily screen-height air temperature, humidity, and wind speed and direction. The snow-transport model is coupled to a wind model that simulates wind flow over the relatively complex topography. Model results indicate that winter winds interact with the ice topographic features to produce alternating surface patterns of snow accumulation and erosion. In addition, model sensitivity simulations suggest that subtle topographic variations, on the order of 5m elevation change over a horizontal distance of 1 to 1.5 km, can lead to snow-accumulation variations that differ by a factor of six. This result is expected to have important consequences regarding the choice of sites for ice-coring efforts in Antarctica and elsewhere.

scholarly journals Abyssal Upwelling and Downwelling Driven by Near-Boundary Mixing

2017 ◽  
Vol 47 (2) ◽  
pp. 261-283 ◽  
Author(s):  
Trevor J. McDougall ◽  
Raffaele Ferrari
Keyword(s):  
Boundary Layers ◽  
Bottom Water ◽  
Volume Transport ◽  
Direct Result ◽  
Antarctic Bottom Water ◽  
Boundary Mixing ◽  
Budget Analysis ◽  
Bottom Boundary Layers ◽  
Stratified Ocean ◽  
Volume Transports

AbstractA buoyancy and volume budget analysis of bottom-intensified mixing in the abyssal ocean reveals simple expressions for the strong upwelling in very thin continental boundary layers and the interior near-boundary downwelling in the stratified ocean interior. For a given amount of Antarctic Bottom Water that is upwelled through neutral density surfaces in the abyssal ocean (between 2000 and 5000 m), up to 5 times this volume flux is upwelled in narrow, turbulent, sloping bottom boundary layers, while up to 4 times the net upward volume transport of Bottom Water flows downward across isopycnals in the near-boundary stratified ocean interior. These ratios are a direct result of a buoyancy budget with respect to buoyancy surfaces, and these ratios are calculated from knowledge of the stratification in the abyss along with the assumed e-folding height that characterizes the decrease of the magnitude of the turbulent diapycnal buoyancy flux away from the seafloor. These strong diapycnal upward and downward volume transports are confined to a few hundred kilometers of the continental boundaries, with no appreciable diapycnal motion in the bulk of the interior ocean.

scholarly journals Laboratory Investigation of the Impact of Lateral Spreading on Buoyancy Flux in a River Plume

2013 ◽  
Vol 43 (12) ◽  
pp. 2588-2610 ◽  
Author(s):  
Yeping Yuan ◽  
Alexander R. Horner-Devine
Keyword(s):  
Control Volume ◽  
River Mouth ◽  
Lateral Spreading ◽  
Buoyancy Flux ◽  
Mixing Processes ◽  
Apparent Paradox ◽  
Plan View ◽  
Image Velocimetry ◽  
Planar Laser ◽  
The Impact

Abstract The relationship between lateral spreading and mixing in stratified gravity currents is investigated by comparing laterally confined and unconfined currents in a series of laboratory experiments. The vertical turbulent buoyancy flux is determined using a control volume approach with velocity and density fields derived from combined particle image velocimetry (PIV) and planar-laser-induced fluorescence (PLIF). Lateral spreading is determined in the unconfined experiments based on plan-view imaging using the optical thickness method (OTM). The authors find that lateral spreading dramatically modifies the plume structure; the spreading plume layer consists of approximately linear density and velocity profiles that extend to the surface, whereas the channelized plume profiles are uniform near the surface. Lateral spreading decreases the average plume density relative to laterally confined currents with similar inflow conditions. However, the local turbulent buoyancy flux in the spreading experiments is approximately equal to that in the confined experiments. This apparent paradox is resolved when the plume areas are taken into account. The total mixing integrated over the horizontal plume area is significantly higher in the spreading experiments. Thus, the experiments suggest that spreading does not appreciably alter the turbulent mixing processes at the base of the plume. However, it significantly increases the area over which this mixing occurs and, through this mechanism, increases the net dilution of river water at a fixed distance from the river mouth. Finally, the authors hypothesize that the spreading does not significantly increase the local turbulent buoyancy flux because spreading occurs preferentially near the surface, whereas buoyancy flux is greatest in the core of the current.

scholarly journals Sediment Transport and Associated Long-term Bathymetric Changes due to Tidal Currents in The Seto Inland Sea, Japan

2021 ◽  
Vol 945 (1) ◽  
pp. 012041
Author(s):  
Motoki Ubara ◽  
Yusuke Uchiyama ◽  
Taichi Kosako
Keyword(s):  
Circulation Model ◽  
Sediment Budget ◽  
Tidal Currents ◽  
Seto Inland Sea ◽  
Shear Stresses ◽  
Topographic Features ◽  
Budget Analysis ◽  
The Seto Inland Sea ◽  
Deposition Processes ◽  
Residual Flows

Abstract The topography of the seafloor is essential for determining physical phenomena such as ocean currents, favorable habitats for marine organisms, optimal vessel navigation, and so on. Prevailing currents and waves, as well as associated shear stresses acting on the ocean floor, are responsible for the formation of typical topographic features including sea caldrons and sandbanks through erosion of bedrock and sediments and their deposition processes. In the Seto Inland Sea (SIS), the most extensive semi-enclosed estuary in Japan, tidal currents affect pronouncedly the formation of seafloor topographic features; however, they have not been fully studied, particularly from a hydrodynamic viewpoint. This study aims to understand bathymetric formation under the predominance of tidal currents in the SIS. A 3-D high-resolution SIS circulation model based on the JCOPE2-ROMS system in a triple-nested configuration was utilized to examine the detailed hydrodynamic processes for the topography formations. A high correlation between the bottom shear stress and the scour depth of the erosive areas was observed, demonstrating that local tidal forcing has continuously been exerted on the seafloor to erode. A diagnostic sediment budget analysis was then conducted for sediments typical of the SIS, that is, gravel, sand, and clay, using the modeled circulation field. The horizontal divergence of the residual flows indicates consistency between divergence (convergence) and erosion (deposition). The sediment budget model also shows that these sediments are generally transported from deep to shallow areas in eroded terrains to form deposited terrains fringing the eroded terrains, whereas sedimentation tendency differs largely from location to location.

Mixed-Layer Budget Analysis of the Diurnal Cycle of Entrainment in Southeast Pacific Stratocumulus

2005 ◽  
Vol 62 (10) ◽  
pp. 3775-3791 ◽  
Author(s):  
Peter Caldwell ◽  
Christopher S. Bretherton ◽  
Robert Wood
Keyword(s):  
Boundary Layer ◽  
Mixed Layer ◽  
Diurnal Cycle ◽  
Liquid Water ◽  
Layer Structure ◽  
Early Morning ◽  
Buoyancy Flux ◽  
Entrainment Rate ◽  
Budget Analysis ◽  
Static Energy

Abstract Mixed-layer budgets of boundary layer mass, moisture, and liquid water static energy are estimated from 6 days of data collected at 20°S, 85°W (a region of persistent stratocumulus) during the East Pacific Investigation of Climate (EPIC) stratocumulus cruise in 2001. These budgets are used to estimate a mean diurnal cycle of entrainment and, by diagnosing the fluxes of humidity and liquid water static energy necessary to maintain a mixed-layer structure, of buoyancy flux. Although the entrainment rates suggested by each of the budgets have significant uncertainty, the various methods are consistent in predicting a 6-day mean entrainment rate of 4 ± 1 mm s−1, with higher values at night and very little entrainment around local noon. The diurnal cycle of buoyancy flux suggests that drizzle, while only a small term in the boundary layer moisture budget, significantly reduces subcloud buoyancy flux and may induce weak decoupling of surface and cloud-layer turbulence during the early morning hours, a structure that is maintained throughout the day by shortwave warming. Finally, the diurnal cycle of entrainment diagnosed from three recently proposed entrainment closures is found to be consistent with the observationally derived values.

scholarly journals Analysis of Vortex Dynamics of Lateral Circulation in a Straight Tidal Estuary*

2014 ◽  
Vol 44 (10) ◽  
pp. 2779-2795 ◽  
Author(s):  
Ming Li ◽  
Peng Cheng ◽  
Robert Chant ◽  
Arnoldo Valle-Levinson ◽  
Kim Arnott
Keyword(s):  
Turbulent Diffusion ◽  
Tidal Cycle ◽  
Salinity Gradient ◽  
Vertical Shear ◽  
Streamwise Vorticity ◽  
Entire Cross Section ◽  
Boundary Mixing ◽  
Budget Analysis ◽  
Lateral Circulation ◽  
Differential Advection

Abstract The dynamics associated with lateral circulation in a tidally driven estuarine channel is analyzed on the basis of streamwise vorticity. Without rotational effects, differential advection and diffusive boundary mixing produce two counterrotating vortices (in the cross-channel section) whose strength and sense of circulation may change during a tidal cycle. The streamwise vorticity equation is determined by a balance between baroclinic forcing and turbulent diffusion, which explains the flood–ebb asymmetry of the lateral circulation. Analysis of the lateral salinity gradient shows that differential advection is the main driver of lateral flows, but boundary mixing can also be an important contributor in stratified estuaries. The strength of lateral circulation decreases with increasing stratification. With rotational effects, the lateral Ekman forcing in the bottom boundary layer drives a one-cell lateral circulation that switches its sense of rotation over the tidal cycle. The vorticity budget analysis reveals a three-way balance among the tilting of planetary vorticity by the vertical shear in the along-channel current, baroclinic forcing, and turbulent diffusion. The structure and magnitude of the lateral circulation change with the width of the estuary, expressed nondimensionally as the Kelvin number Ke. This lateral circulation features two counterrotating vortices in narrow estuaries, one vortex filling up the entire cross section in estuaries of intermediate widths and one vortex confined to the left side (looking into the estuary) in wide estuaries. The magnitude of the streamwise vorticity increases rapidly with Ke, reaches a maximum at , and decreases slightly in wide estuaries subject to strong rotational control.

Filling box flows in porous media

2015 ◽  
Vol 782 ◽  
pp. 455-478 ◽  
Author(s):  
Chunendra K. Sahu ◽  
M. R. Flynn
Keyword(s):  
Porous Medium ◽  
Similarity Solution ◽  
Control Volume ◽  
Salt Water ◽  
Current Source ◽  
Gravity Current ◽  
Gravity Currents ◽  
Horizontal Distance ◽  
Volume Flux ◽  
Reduced Gravity

We report upon a theoretical and experimental investigation of a porous medium ‘filling box’ flow by specifically examining the details of the laminar descending plume and its outflow in a control volume having an impermeable bottom boundary and sidewalls. The plume outflow initially comprises a pair of oppositely directed gravity currents. The gravity currents propagate horizontally until they reach the lateral sidewalls at $y=\pm L$. The flow then becomes of filling box type, with a vertically ascending ‘first front’ separating discharged plume fluid below from ambient fluid above. The flow details are described analytically by first deriving a new similarity solution for Darcy plumes with $\mathit{Pe}>O(1)$, where $\mathit{Pe}$ is the Péclet number. From the similarity solution so obtained, we then derive expressions for the plume volume flux and mean reduced gravity as functions of the vertical distance from the source. Regarding the plume outflow, a similarity solution adopted from Huppert & Woods (J. Fluid Mech., vol. 292, 1995, pp. 55–69) describes the height and front speed of the gravity currents, whereas a semi-implicit finite difference scheme is used to predict the first front elevation versus time and horizontal distance. As with high-Reynolds-number filling box flows, that studied here is an example of a coupled problem: the gravity current source conditions are prescribed by the plume volume flux and mean reduced gravity. Conversely, discharged plume fluid may be re-entrained into the plume, be it soon or long after reaching the bottom impermeable boundary. To corroborate our model predictions, analogue laboratory experiments are performed with fresh water and salt water as the working fluids. Our experiments consider as independent variables the porous medium bead diameter and the plume source volume flux and reduced gravity. Predictions for the gravity current front position and height compare favourably against analogue measured data. Good agreement is likewise noted when considering either the mean elevation or the profile of the first front. Results from this study may be adopted in modelling geological plumes. For example, our equations can be used to predict the time required for discharged plume fluid to return to the point of injection in the case of aquifers closed on the sides and below by impermeable boundaries.

Meridional Circulation, Turbulence, and Diffusion Processes in Stars

1976 ◽  
Vol 32 ◽  
pp. 109-116 ◽  
Author(s):  
S. Vauclair
Keyword(s):  
Convection Zone ◽  
Diffusion Processes ◽  
Meridional Circulation ◽  
Diffusion Time ◽  
Work In Progress ◽  
First Results ◽  
Stellar Envelopes ◽  
And Diffusion ◽  
Turbulence And Diffusion ◽  
Hr Diagram

This paper gives the first results of a work in progress, in collaboration with G. Michaud and G. Vauclair. It is a first attempt to compute the effects of meridional circulation and turbulence on diffusion processes in stellar envelopes. Computations have been made for a 2 Mʘstar, which lies in the Am - δ Scuti region of the HR diagram.Let us recall that in Am stars diffusion cannot occur between the two outer convection zones, contrary to what was assumed by Watson (1970, 1971) and Smith (1971), since they are linked by overshooting (Latour, 1972; Toomre et al., 1975). But diffusion may occur at the bottom of the second convection zone. According to Vauclair et al. (1974), the second convection zone, due to He II ionization, disappears after a time equal to the helium diffusion time, and then diffusion may happen at the bottom of the first convection zone, so that the arguments by Watson and Smith are preserved.

Sign in / Sign up

Export Citation Format

Share Document