Taylor Column Research Articles

Multidisciplinary indicators for confirming the existence and ecological effects of a Taylor column in the Tropical Western Pacific Ocean

The Taylor column, a typical hydrological structure around a seamount, can help to explain the high biomass and biodiversity around the seamount. However, it is difficult to observe a Taylor column in the field because it is easy to be destroyed by the change of ocean environment. Fortunately, a Taylor column around the C4 seamount in the Tropical Western Pacific Ocean was identified during our cruise. The existence of a Taylor column was confirmed by multidisciplinary indicators: 1) the theoretical calculation values of Bl and Ro were 4.922 and 0.195, respectively, indicating the environmental conditions were sufficient for a Taylor column to form; 2) the uplifts of isotherms and isohalines indicated the existence of the upwelling around the C4 seamount summit; 3) the Acoustic Doppler current profilers (ADCP) data indicated the existence of an anticyclonic circulation at the water layers ranging from 200 to 300 m. Meanwhile, the Taylor column's ecological effects were obvious around the seamount. The isolines of the nutrients, chlorophyll a and heterotrophic bacteria had uplifts approximately consistent with isotherms and isohalines, indicating they were influenced by the upwelling in this region. Meanwhile, the planar graphs of these parameters in the water column above 200 m showing the values around the seamount were relatively high, indicating the effects of the Taylor column on the enhancement of productivity. These results further confirmed that a Taylor column indeed formed and caused ecological effects in the C4 seamount. Finally, the scope of the Taylor column was roughly estimated based on the Chl a concentrations, which centered around the station O with a radius of 6.1 km.

Why the most long-lived oceanic vortices are found in the subtropical westward flows

This paper examines factors contributing to the remarkable longevity of coherent vortices in the subtropical westward flows. Baroclinic vortices embedded in large-scale vertical shears generate Rossby waves which form an opposite sign eddy associated with inertial Taylor columns on the beta-plane. The combination of the vortex and lee Rossby wave can be viewed as a hetonic dipole that induces meridional drift and heat flux leading to self-amplification of vortices in baroclinically unstable flows. The analytical tractability is achieved by considering the marginally stable flow, where the beta-effect is nearly compensated by the potential vorticity gradient (PVG) associated with the meridional slope of the density interface. In the two-layer model such compensation can occur in the upper layer with the westward flow or in the lower layer with the eastward flow on top. In baroclinically unstable mean flows, vortices are shown to intensify due to the Lagrangian conservation of potential vorticity inside their cores, drifting meridionally in the layer with negative PVG and supporting baroclinic turbulence. The theory is confirmed by numerical simulations indicating that for westward flows in subtropical oceans, reduced PVG in the upper layer provides favorable conditions for eddy longevity and pathways.

An experimental study on the motion of buoyant particles in the free-surface vortex flow

Experiments are conducted in a Ø600 mm tank to analyse the 3D motion of buoyant particles in the free-surface vortex flow. The experiments revealed two stages in the particle motion: stage 1 is the helical motion along the vortex air core and stage 2 is the axial motion inside the vortex core. The stage 1 motion is sensitive to the particle’s initial conditions by showing a chaotic behaviour and quantified by determining the largest Lyapunov exponent. Consequently, the predictability (forecast horizon) of the particle’s motion is limited. A motion parameter is proposed that indicates if a continuous downward motion along the air core occurs. The dynamics in the stage 2 motion is determined by the imbalance between the particle’s buoyancy force and fluid drag force. The drag appears to be determined by the Taylor column drag force as present in rotating fluids. Based on this force, a motion condition is proposed that indicates if axial motion inside the vortex core occurs.

Columnar vortices induced by dielectrophoretic force in a stationary cylindrical annulus filled with a dielectric liquid

Abstract

Morphological Classification of the Convective Regimes in Rotating Stars

Abstract We present a set of numerical simulations that model the convection zones of solar-like stars. With this suite of numerical experiments, we explore how the nature of the convective structures transitions through a series of morphological regimes as the reduced Rayleigh number increases. Convection first manifests as a belt of rotationally aligned, convective, Taylor columns that circumscribes the equator. As the supercriticality increases, the poles begin to convect, initially in a cellular form, but eventually a plumy form emerges. Finally, at extremely high values of the Rayleigh number, a weakly rotating regime is achieved with antisolar differential rotation, i.e., the equator rotates more slowly than the poles. For all of these regimes, we provide theoretical and empirical scaling relations that summarize how global quantities—such as the bulk Rossby number and Reynolds number—scale with the Rayleigh and Ekman numbers. We demonstrate that a Rossby number based on the properties of the thermal boundary layer that clings to the outer surface of the convection zone works particularly well to predict the transition to antisolar differential rotation.

An analysis in the non-inertial frame: ball in a rotating tube and the Taylor column

In this paper, we consider a small ball placed in a liquid-filled transparent cylinder sealed at both ends. When the tube is inclined and spun about the vertical axis like a centrifuge, a heavy ball (more dense than the liquid) will accelerate to either the top or bottom end of the tube depending on its release position while a light ball (less dense than the liquid) will instead tend towards an equilibrium position in the tube. Experimental measurements of the ball’s motion show large disagreements with Stokes’ theory of drag force on the ball. The formation of a rotating column of liquid induced by the Coriolis force, known as a Taylor column, significantly increases the drag on the ball. In this paper, we aim to investigate the equilibrium position as well as the motion path of the ball, with a numerical solution to the 3D time-dependent Navier–Stokes equation in the rotating frame of the tube, as a function of the inclination angle and angular velocity of rotation of the tube, which are experimentally verified for a ball in a water-filled tube. Increasing both the angular velocity and inclination angle will cause the equilibrium position to shift closer to the bottom of the tube, a faster motion of the ball, and larger deflections to the side of the tube. The formation of the Taylor column was also visualised in the rotating frame with dye injection.

Three-dimensional visualization of columnar vortices in rotating Rayleigh–Bénard convection

To enrich the three-dimensional experimental details of vortex structures in rotating Rayleigh–Benard convection, we established a technique visualizing three-dimensional vortex structures using scanning planar particle image velocimetry. Experiments were performed at fixed Rayleigh number, $$\hbox {Ra} = 1.0 \times 10^7$$ and different Taylor numbers from $$\hbox {Ta} = 6.0 \times 10^6$$ to $$1.0 \times 10^8$$ , corresponding to convective Rossby numbers from $$0.1 \le \hbox {Ro} \le 0.5$$ at which gradual transition between vortical plumes and convective Taylor columns regime is observed. Stream function distributions calculated from horizontal velocity vector fields visualize the vortex structure formed in the regimes. As quantitative information extracted from the visualized structures, distances between vortices recognized on the distributions show a good agreement with that evaluated by a theory. With the accumulated planar stream function distributions and vertical velocity component calculated from the horizontal velocity vectors, the three-dimensional representations of vortices indicate that quasi-two-dimensional columnar vortices straighten in the vertical direction with increasing Ta.

Mean flow anisotropy without waves in rotating turbulence

We tackle the question of how anisotropy in flows subject to background rotation favours structures elongated along the rotation axis, especially in turbulent flows. A new, wave-free mechanism is identified that challenges the current understanding of the process. Inertial waves propagating near the rotation axis are generally accepted as the most efficient mechanism to transport energy anisotropically. They have been shown to transfer energy to large anisotropic, columnar structures. Nevertheless, they cannot account for the formation of simpler steady anisotropic phenomena such as Taylor columns. Here, we experimentally show that more than one mechanism involving the Coriolis force may promote anisotropy. In particular, in the limit of fast rotation, that is at low Rossby number, anisotropy favouring the direction of rotation of the average of a turbulent flow arises neither because of inertial waves nor following the same mechanism as in steady Taylor columns, but from an interplay between the Coriolis force and average advection.

Poleward translation of vortices due to deep thermal convection on a rotating planet

Atmospheres of gas-giant planets are driven by thermal convection and often exhibit cyclonic circulation at the poles. Here we present the results of the numerical simulations of individual cold and warm blobs in a polar area of a rotating deep spherical layer. The simulations show that the cyclones created at the top of the atmosphere by sinking cold blobs translate northward. The cyclones are the surface signatures of the Taylor columns formed above the descending cold blobs. The Taylor columns are aligned with the planetary axis of rotation and are created by inertial (gyroscopic) waves emitted by the blobs. In contrast, the cyclones created at the bottom of the shell by rising warm blobs move southwards. The numerical results exclude beta-drift from possible reasons of the observed translation.

Raymond Hide. 17 May 1929—6 September 2016

Raymond Hide was a physicist who worked at the interfaces between fundamental hydrodynamics, magnetohydrodynamics (MHD), the geophysics of the Earth's interior, atmosphere and oceans and those of other planets. He received his PhD from the University of Cambridge, and spent the majority of his career at the Met Office and then the University of Oxford. In laboratory studies of sloping thermal convection carried out at Cambridge in the early 1950s he discovered various regimes of vacillation and other multiply-periodic intransitive flows as well as aperiodic flows, now recognized as a form of geostrophic turbulence. These findings influenced seminal mathematical studies of what came to be known as deterministic chaos, and provided a paradigm for interpreting large-scale flows in the atmospheres of the Earth and other planets. Related contributions include general theoretical results tested by crucial laboratory experiments on boundary layers, Taylor columns and detached shear layers. His contributions to MHD include the concepts of potential magnetic field and magnetic superhelicity. He also initiated research on the dynamo origin of the magnetic fields of Jupiter and other major planets and its implications for their internal structure and dynamics. His extensive research on fluctuations of the Earth's rotation led to new developments in areas as diverse as meteorology and climatology and studies of the structure and dynamics of the Earth's deep interior.

Micronekton distributions and assemblages at two shallow seamounts of the south-western Indian Ocean: Insights from acoustics and mesopelagic trawl data

Micronekton distributions and assemblages were investigated at two shallow seamounts of the south-western Indian Ocean using a combination of trawl data and a multi-frequency acoustic visualisation technique. La Pérouse seamount (summit depth ~60 m) is located on the outskirts of the oligotrophic Indian South Subtropical Gyre (ISSG) province with weak mesoscale activities and low primary productivity all year round. The “MAD-Ridge” seamount (thus termed in this study; ~240 m) is located in the productive East African Coastal (EAFR) province with high mesoscale activities to the south of Madagascar. Higher micronekton species richness was recorded at MAD-Ridge compared to La Pérouse. Resulting productivity at MAD-Ridge seamount was likely due to the action of mesoscale eddies advecting productivity and larvae from the Madagascar shelf rather than local dynamic processes such as Taylor column formation. Mean micronekton abundance/biomass, as estimated from mesopelagic trawl catches, were lower over the summit compared to the vicinity of the seamounts, due to net selectivity and catchability and depth gradient on micronekton assemblages. Mean acoustic densities in the night shallow scattering layer (SSL: 10–200 m) over the summit were not significantly different compared to the vicinity (within 14 nautical miles) of MAD-Ridge. At La Pérouse and MAD-Ridge, the night and day SSL were dominated by common diel vertically migrant and non-migrant micronekton species respectively. While seamount-associated mesopelagic fishes such as Diaphus suborbitalis (La Pérouse and MAD-Ridge) and Benthosema fibulatum performed diel vertical migrations (DVM) along the seamounts’ flanks, seamount-resident benthopelagic fishes, including Cookeolus japonicus (MAD-Ridge), were aggregated over MAD-Ridge summit. Before sunrise, mid-water migrants initiated their vertical migration from the intermediate to the deep scattering layer (DSL, La Pérouse: 500–650 m; MAD-Ridge: 400–700 m) or deeper. During sunrise, the other taxa contributing to the night SSL exhibited a series of vertical migration events from the surface to the DSL or deeper until all migrants have reached the DSL before daytime. Possible mechanisms leading to the observed patterns in micronekton vertical and horizontal distributions are discussed. This study contributes to a better understanding of how seamounts influence the DVM, horizontal distribution and community composition of micronekton and seamount-associated/resident species at two poorly studied shallow topographic features in the south-western Indian Ocean.

Physical Drivers of Phytoplankton Bloom Initiation in the Southern Ocean's Scotia Sea

AbstractThe Scotia Sea is the site of one of the largest spring phytoplankton blooms in the Southern Ocean. Past studies suggest that shelf‐iron inputs are responsible for the high productivity in this region, but the physical mechanisms that initiate and sustain the bloom are not well understood. Analysis of profiling float data from 2002 to 2017 shows that the Scotia Sea has an unusually shallow mixed‐layer depth during the transition from winter to spring, allowing the region to support a bloom earlier in the season than elsewhere in the Antarctic Circumpolar Current. We compare these results to the mixed‐layer depth in the 1/6° data‐assimilating Southern Ocean State Estimate and then use the model output to assess the physical balances governing mixed‐layer variability in the region. Results indicate the importance of lateral advection of Weddell Sea surface waters in setting the stratification. A Lagrangian particle release experiment run backward in time suggests that Weddell outflow constitutes 10% of the waters in the upper 200 m of the water column in the bloom region. This dense Weddell water subducts below the surface waters in the Scotia Sea, establishing a sharp subsurface density contrast that cannot be overcome by wintertime convection. Profiling float trajectories are consistent with the formation of Taylor columns over the region's complex bathymetry, which may also contribute to the unique stratification. Furthermore, biogeochemical measurements from 2016 and 2017 bloom events suggest that vertical exchange associated with this Taylor column enhances productivity by delivering nutrients to the euphotic zone.

Modeling Ice Shelf Cavities and Tabular Icebergs Using Lagrangian Elements

AbstractMost ocean climate models do not represent ice shelf calving in a physically realistic way, even though the calving of icebergs is a major component of the mass balance for Antarctic ice shelves. The infrequency of large calving events together with the difficulty of placing observational instruments around icebergs means that little is known about how calving icebergs affect the ocean. In this study we present a novel model of an ice shelf coupled to an ocean circulation model, where the ice shelf is constructed of Lagrangian elements that allow simulation of iceberg calving. The Lagrangian ice shelf model is used to simulate the flow beneath a static idealized ice shelf, to verify that it can reproduce the results of an existing Eulerian model simulation with an identical configuration. The Lagrangian model is then used to simulate the ocean's response to a calved iceberg drifting away from the ice shelf. The results show how a calving event and subsequent iceberg drift affect the ocean. At the ice front, the calving event leads to a warming of the ocean surface and cooling of the water column at depth, allowing cooler waters to enter the ice shelf cavity, leading to reduced melt rates within the cavity. A Taylor column is observed below the iceberg, which moves with the iceberg as it drifts into the open ocean. As the iceberg drifts further from the ice shelf, the circulation within the ice shelf cavity tends toward a new steady state, consistent with the new ice shelf geometry.

Environmental characteristics in three seamount areas of the Tropical Western Pacific Ocean: Focusing on nutrients

Nutrients distribution and influencing factors in three seamount areas named Y3, M2 and C4 of the Tropical Western Pacific Ocean (TWPO) were investigated. Nutrients showed obvious uplifts around the three seamounts, consistent with the uplifts of isotherms and isohalines, indicating the existence of a bottom-up process of nutrients. Meanwhile, compared with the stations away from seamount and the reference stations in the TWPO, nutrients concentrations around seamount were much higher. Among the three seamounts, the average nutrients concentrations were highest in Y3, while they were lowest in C4. Moreover, compared with the obvious nitrogen limitation in Y3 and M2, the N:P (13.5:1) and Si:N (6.1:1) were closed to the Redfield ratio. The current-seamount interaction was the determining influencing factor on nutrients distribution, causing the hydrology dynamic changes such as uplifts and Taylor column. Meanwhile, T and S also affected nutrients distribution, especially nutrients and T showed significant negative correlations.

Impact of deep-ocean eddies and fronts on the shelf seas of a sub-Antarctic Archipelago: The Prince Edward Islands

Abstract Ecosystems within the Southern Ocean, such as the Prince Edward Islands (PEIs), fulfil a pivotal role in sustaining rich environments with large populations of top predators. Many of these have already undergone dramatic shifts in response to changes in climate, highlighting the crucial need to enhance our understanding of drivers of oceanographic variability in the region, as well as their impacts on biological communities. Daily averaged bottom temperatures and water-column current speeds from two moorings in the inter-island region, between April 2014 and April 2018, present the first continuous set of high temporal resolution in situ measurements at the PEIs. These data were investigated to determine the influence of passing deep-sea mesoscale eddies and fronts on hydrographic conditions on the inter-island shelf. Warming/cooling events of the order of 0.5–2 °C, sometimes lasting longer than 30 days at a time, concomitant with changes in current speed and direction were associated with advection of waters into the shelf region from passing anticyclonic/cyclonic eddies. Similarly, the impact of frontal movement was quantified by increased current speeds throughout the water column when the southern branch of the sub-Antarctic Front (S-SAF), or the northern branch of the Antarctic Polar Front was in close proximity to the islands. When the S-SAF was located north of the PEIs, bottom temperatures were overall lower due to the stronger influx of Antarctic surface and intermediate waters. In contrast, when the S-SAF was close to or south of the PEIs, bottom temperatures were elevated as a result of the occurrence of larger proportions of warmer, more saline surface and intermediate sub-Antarctic and even Subtropical waters. Notably, the predominance of westerly flow in the southern portion of inter-island region suggested the perpetual existence of a Taylor column which was at times enhanced by the juxtaposition of some eddies.

Convective Models of Jupiter’s Zonal Jets with Realistic and Hyper-Energetic Excitation Source

Numerical simulations of Jupiter’s zonal jets are presented, which are generated with realistic and hyper energetic source. The models are three dimensional and nonlinear, applied to a gas that is convective, stratified and compressible. Two solutions are presented, one for a shallow 0.6% envelope, the other one 5% deep. For the shallow model (SM), Jupiter’s small energy flux was applied with low kinematic viscosity. For the deep model (DM), the energy source and viscosity had to be much larger to obtain a solution with manageable computer time. Alternating zonal winds are generated of order 100 m/s, and the models reproduce the observed width of the prograde equatorial jet and adjacent retrograde jets at 20° latitude. But the height variations of the zonal winds differ markedly. In SM the velocities vary radially with altitude, but in DM Taylor columns are formed. The dynamical properties of these divergent model results are discussed in light of the computed meridional wind velocities. With large planetary rotation rate Ω, the zonal winds are close to geostrophic, and a quantitative measure of that property is the meridional Rossby number, Rom. In the meridional momentum balance, the ratio between inertial and Coriolis forces produces Rom = V2/ΩLU, U zonal, V meridional winds, L horizontal length scale. Our analysis shows that the meridional winds vary with the viscosity like ν1/2. With much larger viscosity and meridional winds, the Rossby number for DM is much larger, Rom(DM) >> Rom(SM). Compared to the shallow model with zonal winds varying radially, the deeper and more viscous model with Taylor columns is much less geostrophic. The zonal winds of numerical models in the literature tend to be independent of the energy source, in agreement with the present results. With 104 times larger energy flux, the zonal winds for DM only increase by a factor of 3, and the answer is provided by the zonal momentum budget with meridional winds, VU/L = ΩV, yielding U = ΩL, independent of the source. The same relationship produces the zonal Rossby number, Roz = U/ΩL, of Order 1, which is commonly used as a dimensionless measure of the zonal wind velocities.

Nonlinear influence of the Earth’s rotation on iceberg melting

The calving of icebergs accounts for a significant fraction of the mass loss from both the Antarctic and Greenland ice sheets. Iceberg melting affects the water properties impacting sea ice formation, local circulation and biological activity. Laboratory experiments have investigated the effects of the Earth’s rotation on iceberg melting and the possible formation of Taylor columns (TCs) underneath icebergs. It is found that at high Rossby number,$Ro$, when rotation is weak compared to advection, iceberg melting is unaffected by the background rotation. As$Ro$decreases, the melt rate shows an increasing trend, which is expected to reverse for very low$Ro$. This behaviour is explained by considering the integrated horizontal velocity at the base of the iceberg. For moderate$Ro$, a partial TC is formed and its effective blocking accelerates the flow under the remainder of the iceberg, which increases the melt rate since the melting is proportional to the flow velocity. It is expected that for very low$Ro$the melt rate decreases because, with the expansion of the TC, the region of flow acceleration occurs away from the base of the iceberg. For low free stream velocity the freshwater produced by the ice melting introduces another dynamical effect. It is observed that there is a threshold free stream velocity below which the melt rate is constant. This is explained with the formation of a gravity current at the base of the iceberg that insulates it from the free flow and controls its melting.

Pebble-trapping Backreaction Does Not Destroy Vortices

The formation of planets remains one of the most challenging problems of contemporary astrophysics. Starting with micron-sized dust grains, coagulation models predict growth up to centimeter (pebbles), but growth beyond this size is difficult because of fragmentation and drift. Ways to bypass this problem have focused on inhomogeneities in the flow, be that zonal flows, streaming instability, or vortices. Because vortices are in equilibrium between the Coriolis and the pressure force, the pressureless grains will orbit along a vortex streamline experiencing a drag force. This is a very effective mechanism to concentrate pebbles as also seen in numerical simulations and possibly in ALMA observations. Yet, a high pebble load is dangerous for the vortex, and we showed that in two-dimensional simulations the backreaction eventually leads to vortex disruption. We investigate whether the same happens in three dimensions. We perform 3D simulations with pebbles in a local box finding that, although the pebbles disturb the vortex around the midplane, the column does not get destroyed. This result is important because, based on the previous 2D result suggesting complete disruption, the vortex interpretation of ALMA observations has been called into question. We show instead that the vortex behaves like a Taylor column, and the pebbles as obstacles to the flow. Pebble accumulation in the center of the vortices proceeds to roughly the same concentration as in the control run without backreaction.

Calibrated Seismic Imaging of Eddy‐Dominated Warm‐Water Transport Across the Bellingshausen Sea, Southern Ocean

AbstractSeismic reflection images of thermohaline circulation from the Bellingshausen Sea, adjacent to the West Antarctica Peninsula, were acquired during February 2015. This survey shows that bright reflectivity occurs throughout the upper 300 m. By calibrating these seismic images with coeval hydrographic measurements, intrusion of warm water features onto the continental shelf at Marguerite and Belgica Troughs is identified and characterized. These features have distinctive lens‐shaped patterns of reflectivity with lengths of 0.75–11.00 km and thicknesses of 100–150 m, suggesting that they are small mesoscale to submesoscale eddies. Abundant eddies are observed along a transect that crosses Belgica Trough. Near Alexander Island Drift, a large, of order km3, bowl‐like feature, that may represent an anticyclonic Taylor column, is imaged on a pair of orthogonal images. A modified iterative procedure is used to convert seismic imagery into maps of temperature that enable the number and size of eddies being transported onto the shelf to be quantified. Finally, analysis of prestack shot records suggests that these eddies are advecting southward at speeds of m s−1, consistent with limited legacy hydrographic measurements. Concentration of observed eddies south of the Southern Antarctic Circumpolar Current Front implies they represent both a dominant, and a long‐lived, mechanism of warm‐water transport, especially across Belgica Trough. Our observations suggest that previous estimates of eddy frequency may have been underestimated by up to 1 order of magnitude, which has significant implications for calculations of ice mass loss on the shelf of the West Antarctic Peninsula.

The Biology of Seamounts: 25 Years on.

Seamounts are one of the major biomes of the global ocean. The last 25 years of research has seen considerable advances in the understanding of these ecosystems. The interactions between seamounts and steady and variable flows have now been characterised providing a better mechanistic understanding of processes influencing biology. Processes leading to upwelling, including Taylor column formation and tidal rectification, have now been defined as well as those leading to draw down of organic matter from the ocean surface to seamount summit and flanks. There is also an improved understanding of the interactions between seamounts, zooplankton and micronekton communities especially with respect to increased predation pressure in the vicinity of seamounts. Evidence has accumulated of the role of seamounts as hot spots for ocean predators including large pelagic fish, sharks, pinnipeds, cetaceans and seabirds. The complexity of benthic communities associated with seamounts is high and drivers of biodiversity are now being resolved. Claims of high endemism resulting from isolation of seamounts as islands of habitat and speciation have not been supported. However, for species characterised by low dispersal capability, such as some groups of benthic sessile or low-mobility invertebrates, low connectivity between seamount populations has been found with evidence of endemism at a local level. Threats to seamounts have increased in the last 25 years and include overfishing, destructive fishing, marine litter, direct and indirect impacts of climate change and potentially marine mining in the near future. Issues around these threats and their management are discussed.