scholarly journals Dynamics of Dense Water Descending a Continental Slope*

2005 ◽  
Vol 35 (8) ◽  
pp. 1318-1328 ◽  
Author(s):  
Hsien-Wang Ou
Keyword(s):  
Continental Slope ◽  
Mechanical Energy ◽  
Frictional Torque ◽  
Geostrophic Balance ◽  
Friction Control ◽  
Dense Water ◽  
Density Anomaly ◽  
Mass Properties ◽  
Model Predictions ◽  
Vorticity Balance

Abstract A reduced-gravity model is used to examine the dynamics of dense water descending a continental slope. The model solves for the geostrophically adjusted state before it is subjected to significant frictional decay. For such bottom-mounted flow, it is argued that frictional torque would dominate the net vorticity balance to equalize the edge flows, resulting in double velocity cores. Constrained by the geostrophic balance, the dense water thus may settle only over a concave bottom and is sheetlike, covering typically the whole slope rise. As such, the adjustment is characterized by a spreading rather than sinking of the layer—with little descent of the upper edge but a swift downslope current propelling the lower edge. Through the mechanical energy balance, it is found in addition that a greater density anomaly would increase the total entrainment flux to more strongly dilute the original anomaly, yielding a product water that is less varied in the water-mass properties. Model predictions compare favorably with some observed dense outflows, in support of the entrainment and friction control of the geostrophic adjustment.

Symmetric and Baroclinic Instability in Dense Shelf Overflows

2019 ◽  
Vol 49 (1) ◽  
pp. 39-61 ◽  
Author(s):  
Elizabeth Yankovsky ◽  
Sonya Legg
Keyword(s):  
Baroclinic Instability ◽  
Gravity Current ◽  
The Arctic ◽  
Neutral Buoyancy ◽  
Buoyancy Forcing ◽  
Dense Water ◽  
Density Anomaly ◽  
Eurasian Basin ◽  
Thermohaline Stratification ◽  
2D And 3D

AbstractIn this study, we revisit the problem of rotating dense overflow dynamics by performing nonhydrostatic numerical simulations, resolving submesoscale variability. Thermohaline stratification and buoyancy forcing are based on data from the Eurasian basin of the Arctic Ocean, where overflows are particularly crucial to the exchange of dense water between shelves and deep basins, yet have been studied relatively little. A nonlinear equation of state is used, allowing proper representation of thermohaline structure and mixing. We examine three increasingly complex scenarios: nonrotating 2D, rotating 2D, and rotating 3D. The nonrotating 2D case behaves according to known theory: the gravity current descends alongslope until reaching a relatively shallow neutral buoyancy level. However, in the rotating cases, we have identified novel dynamics: in both 2D and 3D, the submesoscale range is dominated by symmetric instability (SI). Rotation leads to geostrophic adjustment, causing dense water to be confined within the forcing region longer and attain a greater density anomaly. In the 2D case, Ekman drainage leads to descent of the geostrophic jet, forming a highly dense alongslope front. Beams of negative Ertel potential vorticity develop parallel to the slope, initiating SI and vigorous mixing in the overflow. In 3D, baroclinic eddies are responsible for cross-isobath dense water transport, but SI again develops along the slope and at eddy edges. Remarkably, through two different dynamics, the 2D SI-dominated case and 3D eddy-dominated case attain roughly the same final water mass distribution, highlighting the potential role of SI in driving mixing within certain regimes of dense overflows.

scholarly journals A Numerical Investigation of Formation and Variability of Antarctic Bottom Water off Cape Darnley, East Antarctica

2014 ◽  
Vol 44 (11) ◽  
pp. 2921-2937 ◽  
Author(s):  
Yoshihiro Nakayama ◽  
Kay I. Ohshima ◽  
Yoshimasa Matsumura ◽  
Yasushi Fukamachi ◽  
Hiroyasu Hasumi
Keyword(s):  
Sea Ice ◽  
Continental Slope ◽  
Bottom Water ◽  
Heat Budget ◽  
East Antarctica ◽  
Salt Flux ◽  
Ice Formation ◽  
Minor Importance ◽  
Antarctic Bottom Water ◽  
Dense Water

Abstract At several locations around Antarctica, dense water is formed as a result of intense sea ice formation. When this dense water becomes sufficiently denser than the surrounding water, it descends the continental slope and forms Antarctic Bottom Water (AABW). This study presents the AABW formation off the coast of Cape Darnley [Cape Darnley Bottom Water (CDBW)] in East Antarctica, using a nonhydrostatic model. The model is forced for 8 months by a temporally uniform surface salt flux (because of sea ice formation) estimated from Advanced Microwave Scanning Radiometer for Earth Observing System (EOS; AMSR-E) data and a heat budget calculation. The authors reproduce AABW formation and associated periodic downslope flows of dense water. Descending pathways of dense water are largely determined by the topography; most dense water flows into depressions on the continental shelf, advects onto the continental slope, and is steered downslope to greater depths by the canyons. Intense sea ice formation is the most important factor in the formation of AABW off Cape Darnley, and the existence of depressions is of only minor importance for the flux of CDBW. The mechanism responsible for the periodic downslope flow of dense water is further analyzed using an idealized model setup. The period of dense water outflow is regulated primarily by the topographic beta effect.

The global dominance of the Atlantic circulation, seen through boundary pressures.

2020 ◽  
Author(s):  
Chris W. Hughes ◽  
Joanne Williams ◽  
Adam Blaker ◽  
Andrew C. Coward
Keyword(s):  
Continental Slope ◽  
Large Scale ◽  
Strong Influence ◽  
Atlantic Meridional Overturning Circulation ◽  
Ocean Model ◽  
Meridional Overturning Circulation ◽  
Mesoscale Variability ◽  
Bottom Pressure ◽  
Meridional Overturning ◽  
Vorticity Balance

<p>The rapid propagation of boundary waves (or, equivalently, the strong influence of topography on vorticity balance) ensures that bottom pressure along the global continental slope reflects large scale ocean processes, making it possible to see through the fog of the mesoscale, which obscures many observable quantities. This fact is exploited in systems to monitor the Atlantic Meridional Overturning Circulation (AMOC). Here, we use diagnostics from an ocean model with realistic mesoscale variability to demonstrate two things. First: boundary pressures form an efficient method of monitoring AMOC variability. Second: pressures are remarkably constant along isobaths around the global continental slope, varying by less than 5 cm sea-level-equivalent over vast distances below the directly wind-driven circulation. In the latter context, the AMOC stands out as a clear exception, leading to a link between the AMOC and differences in the hydrography of entire ocean basins.</p>

scholarly journals Slackness between vessel and myocardium is necessary for coronary flow reserve

2012 ◽  
Vol 302 (11) ◽  
pp. H2230-H2242 ◽  
Author(s):  
Jonathan M. Young ◽  
Jenny S. Choy ◽  
Ghassan S. Kassab ◽  
Yoram Lanir
Keyword(s):  
Coronary Flow Reserve ◽  
Coronary Flow ◽  
Mechanical Energy ◽  
Potential Effect ◽  
Experimental Measurements ◽  
Flow Reserve ◽  
Model Predictions ◽  
Effectiveness And Efficiency ◽  
Vessel Resistance ◽  
Experimental Findings

Tone regulation in coronary microvessels has largely been studied in isolated vessels in the absence of myocardial tethering. Here, the potential effect of radial tethering and interstitial space connective tissue (ISCT) between coronary microvessels and the surrounding myocardium was studied. We hypothesized that rigid tethering between microvessels and the myocardium would constrain the active contraction of arterioles and is not compatible with the observed tone regulation. The ISCT between coronary microvessels and myocardium in five swine was found to increase exponentially from 0.22 ± 0.02 μm in capillaries (modified Strahler order 0) of the endocardium to 34.9 ± 7.1 μm in epicardial vessels ( order 10). Microvessels with both soft tethering and ISCT gap were capable of significant changes in vessel resistance (up to an ∼1,600% increase), consistent with experimental measurements of high coronary flow reserve. Additionally, the mechanical energy required for myogenic contraction was estimated. The results indicate that rigid tethering requires up to four times more mechanical energy than soft tethering in the absence of a gap. Hence, the experimental measurements and model predictions suggest that effectiveness and efficiency in tone regulation can be achieved only if the vessel is both softly tethered to and separated from the myocardium in accordance with the experimental findings of ISCT gap. These results have fundamental implications on future simulations of coronary circulation.

Laboratory Experiments of Dense Water Descending on Continental Slope

1993 ◽  
pp. 333-350 ◽  
Author(s):  
Yutaka Nagata ◽  
Ryuji Kimura ◽  
Hiroyuki Honji ◽  
Yasuhiro Yamazaki ◽  
Kazuhiro Kawaguchi ◽  
...  
Keyword(s):  
Continental Slope ◽  
Laboratory Experiments ◽  
Dense Water

scholarly journals Enhancement of rotational vacuum friction by surface photon tunneling

Nanophotonics ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 537-543
Author(s):  
Zhujing Xu ◽  
Zubin Jacob ◽  
Tongcang Li
Keyword(s):  
Mechanical Energy ◽  
Film Coating ◽  
Ferroelectric Ceramic ◽  
Frictional Torque ◽  
Thin Film Coating ◽  
Rotating Sphere ◽  
Photon Tunneling ◽  
Barium Strontium ◽  
Large Enhancement ◽  
First Time

AbstractWhen a neutral sphere is rotating near a surface in vacuum, it will experience a frictional torque due to quantum and thermal electromagnetic fluctuations. Such vacuum friction has attracted many interests but has been too weak to be observed. Here we investigate the vacuum frictional torque on a barium strontium titanate (BST) nanosphere near a BST surface. BST is a perovskite ferroelectric ceramic that can have large dielectric responses at GHz frequencies. At resonant rotating frequencies, the mechanical energy of motion can be converted to electromagnetic energy through resonant photon tunneling, leading to a large enhancement of the vacuum friction. The calculated vacuum frictional torques at resonances at sub-GHz and GHz frequencies are several orders larger than the minimum torque measured by an optically levitated nanorotor recently, and are thus promising to be observed experimentally. Moreover, we calculate the vacuum friction on a rotating sphere near a layered surface for the first time. By optimizing the thickness of the thin-film coating, the frictional torque can be further enhanced by several times.

Balance in non-hydrostatic rotating stratified turbulence

2008 ◽  
Vol 596 ◽  
pp. 201-219 ◽  
Author(s):  
WILLIAM J. McKIVER ◽  
DAVID G. DRITSCHEL
Keyword(s):  
Gravity Waves ◽  
Potential Vorticity ◽  
Acoustic Waves ◽  
Buoyancy Frequency ◽  
Scaling Analysis ◽  
Stratified Turbulence ◽  
Dynamical Equations ◽  
Geostrophic Balance ◽  
Vorticity Balance ◽  
Inertia Gravity Waves

It is now well established that two distinct types of motion occur in geophysical turbulence: slow motions associated with potential vorticity advection and fast oscillations due to inertia–gravity waves (or acoustic waves). Many studies have theorized the existence of a flow for which the entire motion is controlled by the potential vorticity (or one ‘master variable’) – this is known as balance. In real geophysical flows, deviations from balance in the form of inertia–gravity waves or ‘imbalance’ have often been found to be small. Here we examine the extent to which balance holds in rotating stratified turbulence which is nearly balanced initially.Using the non-hydrostatic fluid dynamical equations under the Boussinesq approximation, we analyse properties of rotating stratified turbulence spanning a range of Rossby numbers (Ro≡|ζ|max/f) and the frequency ratios (c≡N/f) where ζ is the relative vertical vorticity, f is the Coriolis frequency and N is the buoyancy frequency. Using a recently introduced diagnostic procedure, called ‘optimal potential vorticity balance’, we extract the balanced part of the flow in the simulations and assess how the degree of imbalance varies with the above parameters.We also introduce a new and more efficient procedure, building upon a quasi-geostrophic scaling analysis of the complete non-hydrostatic equations. This ‘nonlinear quasi-geostrophic balance’ procedure expands the equations of motion to second order in Rossby number but retains the exact (unexpanded) definition of potential vorticity. This proves crucial for obtaining an accurate estimate of balanced motions. In the analysis of rotating stratified turbulence at Ro≲1 and N/f≫1, this procedure captures a significantly greater fraction of the underlying balance than standard (linear) quasi-geostrophic balance (which is based on the linearized equations about a state of rest). Nonlinear quasi-geostrophic balance also compares well with optimal potential vorticity balance, which captures the greatest fraction of the underlying balance overall.More fundamentally, the results of these analyses indicate that balance dominates in carefully initialized simulations of freely decaying rotating stratified turbulence up to O(1) Rossby numbers when N/f≫1. The fluid motion exhibits important quasi-geostrophic features with, in particular, typical height-to-width scale ratios remaining comparable to f/N.

scholarly journals Humans optimally anticipate and compensate for an uneven step during walking

eLife ◽  
2022 ◽  
Vol 11 ◽  
Author(s):  
Osman Darici ◽  
Arthur D Kuo
Keyword(s):  
Human Subjects ◽  
Mechanical Energy ◽  
Bipedal Walking ◽  
Time Of Arrival ◽  
Dynamic Prediction ◽  
Simple Task ◽  
Model Predictions ◽  
Steady Level ◽  
Speed Fluctuation ◽  
Energy Economy

The simple task of walking up a sidewalk curb is actually a dynamic prediction task. The curb is a disturbance that could cause a loss of momentum if not anticipated and compensated for. It might be possible to adjust momentum sufficiently to ensure undisturbed time of arrival, but there are infinite possible ways to do so. Much of steady, level gait is determined by energy economy, which should be at least as important with terrain disturbances. It is, however, unknown whether economy also governs walking up a curb, and whether anticipation helps. Here we show that humans compensate with an anticipatory pattern of forward speed adjustments, predicted by a criterion of minimizing mechanical energy input. The strategy is mechanistically predicted by optimal control for a simple model of bipedal walking dynamics, with each leg's push-off work as input. Optimization predicts a tri-phasic trajectory of speed (and thus momentum) adjustments, including an anticipatory phase. In experiment, human subjects ascend an artificial curb with the predicted tri-phasic trajectory, which approximately conserves overall walking speed relative to undisturbed flat ground. The trajectory involves speeding up in a few steps before the curb, losing considerable momentum from ascending it, and then regaining speed in a few steps thereafter. Descending the curb entails a nearly opposite, but still anticipatory, speed fluctuation trajectory, in agreement with model predictions that speed fluctuation amplitudes should scale linearly with curb height. The fluctuation amplitudes also decrease slightly with faster average speeds, also as predicted by model. Humans can reason about the dynamics of walking to plan anticipatory and economical control, even with a sidewalk curb in the way.

scholarly journals Subthermocline Eddies over the Washington Continental Slope as Observed by Seagliders, 2003–09

2013 ◽  
Vol 43 (10) ◽  
pp. 2025-2053 ◽  
Author(s):  
Noel A. Pelland ◽  
Charles C. Eriksen ◽  
Craig M. Lee
Keyword(s):  
Continental Slope ◽  
Current System ◽  
California Current ◽  
Frictional Torque ◽  
California Current System ◽  
The Core ◽  
Northern California Current ◽  
Order Of Magnitude ◽  
Offshore Transport ◽  
Anticyclonic Eddies

Abstract In the California Current System, subthermocline, lenslike anticyclonic eddies generated within the California Undercurrent (CU) are one mechanism for lateral transport of the warm, saline waters of the CU. Garfield et al. established the name “Cuddies” for eddies of this type and hypothesized that they account for a significant fraction of the offshore transport of CU water. This study presents observations of subthermocline eddies collected from a time series of Seaglider surveys in the northern California Current System. Gliders made 46 crossings of subthermocline anticyclones and 17 crossings of subthermocline cyclones over 5.5 yr. Close inspection grouped these into 20 distinct anticyclones and 10 distinct cyclones. Water properties at the core of anticyclonic eddies were similar to those in the core of the CU over the continental slope; these anticyclones are examples of Cuddies. Anticyclonic (cyclonic) eddies had average radii of 20.4 (20.6) km, peak azimuthal current speeds of 0.25 (0.23) m s−1, and average core anomalies of potential vorticity 65% below (125% above) ambient values. Anticyclones contained an order of magnitude greater available heat and salt anomaly relative to background conditions than cyclones on average. Circumstantial evidence of eddy decay through lateral intrusions was found although this was not observed consistently. Observed eddy properties and the geometry of flow over the continental slope were consistent with eddy formation due to frictional torque acting on the CU. Loss of heat and salt from the CU due to subthermocline eddies is estimated to account for 44% of the freshening and cooling of the CU as it flows poleward.

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