Bishakhdatta Gayen

Boundary layer profiles during melting of the sloping ice shelves

Publisher: Australian Antarctic Data Centre

Date: 2018

DOI: 10.4225/15/5B0224D8BA453

PSI to turbulence during internal wave beam refraction through the upper ocean pycnocline

Publisher: American Geophysical Union (AGU)

Date: 16-12-2014

DOI: 10.1002/2014GL061226

Ocean gyres driven by surface buoyancy forcing

Publisher: Wiley

Date: 19-05-2020

DOI: 10.1002/ESSOAR.10503133.1

Development of a novel wind to electrical energy converter of passive ferrofluid levitation through its parameter modelling and optimization

Publisher: Elsevier BV

Date: 12-2021

DOI: 10.1016/J.SETA.2021.101641

Algebraic and exponential instabilities in a sheared micropolar granular fluid

Publisher: Cambridge University Press (CUP)

Date: 19-10-2006

DOI: 10.1017/S002211200600214X

The role of double-diffusive convection in basal melting of Antarctic ice shelves

Publisher: Proceedings of the National Academy of Sciences

Date: 05-02-2021

DOI: 10.1073/PNAS.2007541118

Abstract: Ocean-driven melting of ice shelves is a leading cause of mass loss from Antarctica. However, the small-scale ocean processes responsible for melting are poorly understood due to the difficulty of making direct measurements in these hard to reach environments. Here, we use a high-resolution ocean model to fill this knowledge gap. At low current speeds and relatively warm ocean temperatures, we show that a small-scale ocean process called double-diffusive convection controls ice shelf melt rates and turbulent mixing, forming a unique “staircase” structure beneath the ice. This process is currently missing from ocean–climate models, which consider only turbulent melting due to ocean currents.

Negative turbulent production during flow reversal in a stratified oscillating boundary layer on a sloping bottom

Publisher: AIP Publishing

Date: 10-2011

DOI: 10.1063/1.3651359

Abstract: Three-dimensional direct numerical simulations are performed to model an internal tidal beam at near-critical slope, and the phase dependence of turbulent processes is investigated. Convective instability leads to density overturns that originate in the upper flank of the beam and span the beam width of 6 m during flow reversal from downslope to upslope boundary motion. During this flow reversal event, negative turbulent production is observed signaling energy transfer from velocity fluctuations to the mean flow. In this note, we explain the mechanism underlying negative production.

The Sensitivity of the Antarctic Ice Sheet to a Changing Climate: Past, Present, and Future

Publisher: American Geophysical Union (AGU)

Date: 11-11-2020

DOI: 10.1029/2019RG000663

Abstract: The Antarctic Ice Sheet (AIS) is out of equilibrium with the current anthropogenic‐enhanced climate forcing. Paleoenvironmental records and ice sheet models reveal that the AIS has been tightly coupled to the climate system during the past and indicate the potential for accelerated and sustained Antarctic ice mass loss into the future. Modern observations by contrast suggest that the AIS has only just started to respond to climate change in recent decades. The maximum projected sea level contribution from Antarctica to 2100 has increased significantly since the Intergovernmental Panel on Climate Change (IPCC) 5th Assessment Report, although estimates continue to evolve with new observational and theoretical advances. This review brings together recent literature highlighting the progress made on the known processes and feedbacks that influence the stability of the AIS. Reducing the uncertainty in the magnitude and timing of the future sea level response to AIS change requires a multidisciplinary approach that integrates knowledge of the interactions between the ice sheet, solid Earth, atmosphere, and ocean systems and across time scales of days to millennia. We start by reviewing the processes affecting AIS mass change, from atmospheric and oceanic processes acting on short time scales (days to decades), through to ice processes acting on intermediate time scales (decades to centuries) and the response to solid Earth interactions over longer time scales (decades to millennia). We then review the evidence of AIS changes from the Pliocene to the present and consider the projections of global sea level rise and their consequences. We highlight priority research areas required to improve our understanding of the processes and feedbacks governing AIS change.

Eddy‐Freshwater Interaction Using Regional Ocean Modeling System in the Bay of Bengal

Publisher: American Geophysical Union (AGU)

Date: 28-03-2023

DOI: 10.1029/2022JC019439

Abstract: Eddy‐freshwater interaction is studied in the north Bay of Bengal (BoB) with a high‐resolution simulation using the Regional Ocean Modeling System. Following observations, the model simulates the trapping and homogenization of river water by a cyclonic mesoscale eddy on a submonthly time scale from October to November 2015. As fresh river water is trapped in the eddy, it is characterized by strong vertical and lateral gradients in salinity. Within a few weeks, these gradients relax along with the progressive homogenization of freshwater within the eddy. A mixed‐layer salinity budget shows the importance of ageostrophic vertical advection in addition to lateral advection during the evolution of salinity within the eddy. An analysis of the eddy kinetic energy (EKE) budget in the upper ocean indicates the development of barotropic and baroclinic instabilities. The vertical profiles of EKE conversion terms reveal that the surface freshwater was involved in the evolution of baroclinic instability within the mixed layer. In addition, an eddy available potential energy (EPE) budget shows that the entrainment of the river water raises the EPE, which is due to an increase in lateral salinity gradients across the eddy during the trapping event. Subsequently, the salinity homogenization leads to a decrease in the EPE, and its rate of decay is modulated by a correlation between surface buoyancy fluxes and density anomalies. Finally, reanalysis data show similar trapping and homogenization of freshwater events across multiple years, highlighting the importance of this mechanism on the subseasonal time scale in the BoB.

Turbulence during the generation of internal tide on a critical slope

Publisher: American Physical Society (APS)

Date: 27-05-2010

DOI: 10.1103/PHYSREVLETT.104.218502

Tidal conversion and turbulence at a model ridge: Direct and large eddy simulations

Publisher: Cambridge University Press (CUP)

Date: 09-01-2013

DOI: 10.1017/JFM.2012.513

Abstract: Direct and large eddy simulations are performed to study the internal waves generated by the oscillation of a barotropic tide over a model ridge of triangular shape. The objective is to go beyond linear theory and assess the role of nonlinear interactions including turbulence in situations with low tidal excursion number. The criticality parameter, defined as the ratio of the topographic slope to the characteristic slope of the tidal rays, is varied from subcritical to supercritical values. The barotropic tidal forcing is also systematically increased. Numerical results of the energy conversion are compared with linear theory and, in laminar flow at low forcing, they agree well in subcritical and supercritical cases but not at critical slope angle. In critical and supercritical cases with higher forcing, there are convective overturns, turbulence and significant reduction (as much as 25 %) of the radiated wave flux with respect to laminar flow results. Analysis of the baroclinic energy budget and spatial modal analysis are performed to understand the reduction. The near-bottom velocity is intensified at critical angle slope leading to a radiated internal wave beam as well as an upslope bore of cold water with a thermal front. In the critical case, the entire slope has turbulence while, in the supercritical case, turbulence originates near the top of the topography where the slope angle transitions through the critical value. The phase dependence of turbulence within a tidal cycle is examined and found to differ substantially between the ridge slope and the ridge top where the beams from the two sides cross.

Mixing and dissipation in a geostrophic buoyancy‐driven circulation

Publisher: American Geophysical Union (AGU)

Date: 08-2016

DOI: 10.1002/2016JC011691

Effect of Coulomb friction on orientational correlation and velocity distribution functions in a sheared dilute granular gas

Publisher: American Physical Society (APS)

Date: 12-08-2011

DOI: 10.1103/PHYSREVE.84.021304

Double‐Diffusive Layer and Meltwater Plume Effects on Ice Face Scalloping in Phase‐Change Simulations

Publisher: American Geophysical Union (AGU)

Date: 29-08-2023

DOI: 10.1029/2023GL104396

Abstract: Antarctic ice shelves are losing mass at increasing rates, yet the ice‐ocean interactions that cause significant ice loss are not well understood. A new approach of high‐resolution phase‐change simulations is used to model vertical ice melting into a stratified ocean. The ocean dynamics show complicated interplay between a turbulent buoyant meltwater plume and double‐diffusive layers, while the ice actively melts and changes topography. At room temperatures, the double‐diffusive layer thickness is closely linked to ice scalloping. At lower, more realistic ocean temperatures, the meltwater plume becomes prominent with a laminar‐to‐turbulent transition imprinting an indent on the melting ice. The double‐diffusive layer thickness is consistent with scaling prediction, while the real‐world application demonstrates reasonably good matching of the scaling prediction for some Antarctic regions. Our study is a key first step toward the future use of high‐resolution phase‐change fluid dynamics simulations to better understand Antarctic ice shelves in a changing climate.

Available potential energy in Rayleigh–Bénard convection

Publisher: Cambridge University Press (CUP)

Date: 09-08-2013

DOI: 10.1017/JFM.2013.353

Abstract: The mechanical energy budget for thermally equilibrated Rayleigh–Bénard convection is developed theoretically, with explicit consideration of the role of available potential energy, this being the form in which all the mechanical energy for the flow is supplied. The analysis allows derivation for the first time of a closed analytical expression relating the rate of mixing in symmetric fully developed convection to the rate at which available potential energy is supplied by the thermal forcing. Only about half this supplied energy is dissipated viscously. The remainder is consumed by mixing acting to homogenize the density field. This finding is expected to apply over a wide range of Rayleigh and Prandtl numbers for which the Nusselt number is significantly greater than unity. Thus convection at large Rayleigh number involves energetically efficient mixing of density variations. In contrast to conventional approaches to Rayleigh–Bénard convection, the dissipation of temperature or density variance is shown not to be of direct relevance to the mechanical energy budget. Thus, explicit recognition of available potential energy as the source of mechanical energy for convection, and of both mixing and viscous dissipation as the sinks of this energy, could be of further use in understanding the physics.

Large eddy simulation of a stratified boundary layer under an oscillatory current

Publisher: Cambridge University Press (CUP)

Date: 17-12-2010

DOI: 10.1017/S002211200999200X

Abstract: A numerical study based on large eddy simulation is performed to investigate a bottom boundary layer under an oscillating tidal current. The focus is on the boundary layer response to an external stratification. The thermal field shows a mixed layer that is separated from the external stratified fluid by a thermocline. The mixed layer grows slowly in time with an oscillatory modulation by the tidal flow. Stratification strongly affects the mean velocity profiles, boundary layer thickness and turbulence levels in the outer region although the effect on the near-bottom unstratified fluid is relatively mild. The turbulence is asymmetric between the accelerating and decelerating stages. The asymmetry is more pronounced with increasing stratification. There is an overshoot of the mean velocity in the outer layer this jet is linked to the phase asymmetry of the Reynolds shear stress gradient by using the simulation data to examine the mean momentum equation. Depending on the height above the bottom, there is a lag of the maximum turbulent kinetic energy, dissipation and production with respect to the peak external velocity and the value of the lag is found to be influenced by the stratification. Flow instabilities and turbulence in the bottom boundary layer excite internal gravity waves that propagate away into the ambient. Unlike the steady case, the phase lines of the internal waves change direction during the tidal cycle and also from near to far field. The frequency spectrum of the propagating wave field is analysed and found to span a narrow band of frequencies clustered around 45°.

Meltrate of basal ice shelves at difference inclination

Publisher: Australian Antarctic Data Centre

Date: 2018

DOI: 10.4225/15/5B022497C7B72

Eddy Induced Trapping and Homogenization of Freshwater in the Bay of Bengal

Publisher: American Geophysical Union (AGU)

Date: 06-2021

DOI: 10.1029/2021JC017180

Abstract: Freshwater from rivers influences Indian summer monsoon rainfall and tropical cyclones by stratifying the upper layer and warming the subsurface ocean in the Bay of Bengal (BoB). Here, we use in situ and satellite data with reanalysis to showcase how river water experiences a significant increase in salinity on sub‐seasonal timescales. This involves the trapping and homogenization of freshwater by a cyclonic eddy in the Bay. Using a specific ex le from 2015, river water is shown to enter an eddy along its attracting manifolds within a period of 2 weeks. This leads to the formation of a highly stratified subsurface layer within the eddy. When freshest, the eddy has the largest sea‐level anomaly, spins fastest, and supports strong lateral gradients in salinity. Subsequently, observations reveal a progressive increase in salinity inside the eddy within a month. In particular, salty water spirals in, and freshwater is pulled out across the eddy boundary. Lagrangian experiments elucidate this process, whereby horizontal chaotic mixing provides a mechanism for the rapid increase in surface salinity. A salinity budget also suggests that horizontal advection explains much of the change in mixed layer salinity. Further, the adjustment of this freshwater eddy triggers submesoscale dynamics which appear to be an integral part of the process of salinity homogenization. This pathway is distinct from vertical diffusive mixing and is likely to be important for the evolution of salinity in the BoB.

Ocean Convection

Publisher: MDPI AG

Date: 12-10-2017

DOI: 10.3390/FLUIDS6100360

Abstract: Ocean convection is a key mechanism that regulates heat uptake, water-mass transformation, CO2 exchange, and nutrient transport with crucial implications for ocean dynamics and climate change. Both cooling to the atmosphere and salinification, from evaporation or sea-ice formation, cause surface waters to become dense and down-well as turbulent convective plumes. The upper mixed layer in the ocean is significantly deepened and sustained by convection. In the tropics and subtropics, night-time cooling is a main driver of mixed layer convection, while in the mid- and high-latitude regions, winter cooling is key to mixed layer convection. Additionally, at higher latitudes, and particularly in the sub-polar North Atlantic Ocean, the extensive surface heat loss during winter drives open-ocean convection that can reach thousands of meters in depth. On the Antarctic continental shelf, polynya convection regulates the formation of dense bottom slope currents. These strong convection events help to drive the immense water-mass transport of the globally-spanning meridional overturning circulation (MOC). However, convection is often highly localised in time and space, making it extremely difficult to accurately measure in field observations. Ocean models such as global circulation models (GCMs) are unable to resolve convection and turbulence and, instead, rely on simple convective parameterizations that result in a poor representation of convective processes and their impact on ocean circulation, air–sea exchange, and ocean biology. In the past few decades there has been markedly more observations, advancements in high-resolution numerical simulations, continued innovation in laboratory experiments and improvement of theory for ocean convection. The impacts of anthropogenic climate change on ocean convection are beginning to be observed, but key questions remain regarding future climate scenarios. Here, we review the current knowledge and future direction of ocean convection arising from sea–surface interactions, with a focus on mixed layer, open-ocean, and polynya convection.

Transport by deep convection in basin-scale geostrophic circulation: turbulence-resolving simulations

Publisher: Cambridge University Press (CUP)

Date: 26-02-2019

DOI: 10.1017/JFM.2019.64

Abstract: Direct numerical simulations are used to investigate the nature of fully resolved small-scale convection and its role in large-scale circulation in a rotating $f$ -plane rectangular basin with imposed surface temperature difference. The large-scale circulation has a horizontal geostrophic component and a deep vertical overturning. This paper focuses on convective circulation with no wind stress, and buoyancy forcing sufficiently strong to ensure turbulent convection within the thermal boundary layer (horizontal Rayleigh numbers $Ra\\approx 10^{12}{-}10^{13}$ ). The dynamics are found to depend on the value of a convective Rossby number, $Ro_{\\unicode[STIX]{x0394}T}$ , which represents the strength of buoyancy forcing relative to Coriolis forces. Vertical convection shifts from a mean endwall plume under weak rotation ( $Ro_{\\unicode[STIX]{x0394}T} ^{-1}$ ) to ‘open ocean’ chimney convection plus mean vertical plumes at the side boundaries under strong rotation ( $Ro_{\\unicode[STIX]{x0394}T} ^{-1}$ ). The overall heat throughput, horizontal gyre transport and zonally integrated overturning transport are then consistent with scaling predictions for flow constrained by thermal wind balance in the thermal boundary layer coupled to vertical advection–diffusion balance in the boundary layer. For small Rossby numbers relevant to circulation in an ocean basin, vertical heat transport from the surface layer into the deep interior occurs mostly in ‘open ocean’ chimney convection while most vertical mass transport is against the side boundaries. Both heat throughput and the mean circulation (in geostrophic gyres, boundary currents and overturning) are reduced by geostrophic constraints.

Ablation of sloping ice faces into polar seawater

Publisher: Cambridge University Press (CUP)

Date: 28-01-2019

DOI: 10.1017/JFM.2018.970

Abstract: The effects of the slope of an ice–seawater interface on the mechanisms and rate of ablation of the ice by natural convection are examined using turbulence-resolving simulations. Solutions are obtained for ice slopes $\\unicode[STIX]{x1D703}=2^{\\circ }{-}90^{\\circ }$ , at a fixed ambient salinity and temperature, chosen to represent common Antarctic ocean conditions. For laminar boundary layers the ablation rate decreases with height, whereas in the turbulent regime the ablation rate is found to be height independent. The simulated laminar ablation rates scale with $(\\sin \\unicode[STIX]{x1D703})^{1/4}$ , whereas in the turbulent regime it follows a $(\\sin \\unicode[STIX]{x1D703})^{2/3}$ scaling, both consistent with the theoretical predictions developed here. The reduction in the ablation rate with shallower slopes arises as a result of the development of stable density stratification beneath the ice face, which reduces turbulent buoyancy fluxes to the ice. The turbulent kinetic energy budget of the flow shows that, for very steep slopes, both buoyancy and shear production are drivers of turbulence, whereas for shallower slopes shear production becomes the dominant mechanism for sustaining turbulence in the convective boundary layer.

The Impact of Turbulence and Convection on Transport in the Southern Ocean

Publisher: American Geophysical Union (AGU)

Date: 06-2019

DOI: 10.1029/2018JC014883

Ultra-low friction self-levitating nanomagnetic fluid bearing for highly efficient wind energy harvesting

Publisher: Elsevier BV

Date: 08-2022

DOI: 10.1016/J.SETA.2022.102024

The Dynamics of Mixed Layer Deepening during Open-Ocean Convection

Publisher: American Meteorological Society

Date: 06-2020

DOI: 10.1175/JPO-D-19-0264.1

Abstract: Open-ocean convection is a common phenomenon that regulates mixed layer depth and ocean ventilation in the high-latitude oceans. However, many climate model simulations overestimate mixed layer depth during open-ocean convection, resulting in excessive formation of dense water in some regions. The physical processes controlling transient mixed layer depth during open-ocean convection are examined using two different numerical models: a high-resolution, turbulence-resolving nonhydrostatic model and a large-scale hydrostatic ocean model. An isolated destabilizing buoyancy flux is imposed at the surface of both models and a quasi-equilibrium flow is allowed to develop. Mixed layer depth in the turbulence-resolving and large-scale models closely aligns with existing scaling theories. However, the large-scale model has an anomalously deep mixed layer prior to quasi-equilibrium. This transient mixed layer depth bias is a consequence of the lack of resolved turbulent convection in the model, which delays the onset of baroclinic instability. These findings suggest that in order to reduce mixed layer biases in ocean simulations, parameterizations of the connection between baroclinic instability and convection need to be addressed.

Textile-based piezocatalytic platform for organics degradation under low-frequency water flow

Publisher: Royal Society of Chemistry (RSC)

Date: 2023

DOI: 10.1039/D2TA09682J

Abstract: This work presents the unique advantage of textiles in constructing piezocatalytic platforms. The mesoporous and intertwined textile could lify the striking force of water flow, by which piezocatalysis under low-frequency water flow is achieved.

Degradation of an internal wave beam by parametric subharmonic instability in an upper ocean pycnocline

Publisher: American Geophysical Union (AGU)

Date: 09-2013

DOI: 10.1002/JGRC.20321

Boundary mixing by density overturns in an internal tidal beam

Publisher: American Geophysical Union (AGU)

Date: 07-2011

DOI: 10.1029/2011GL048135

Roles of Shear and Convection in Driving Mixing in the Ocean

Publisher: American Geophysical Union (AGU)

Date: 09-02-2021

DOI: 10.1029/2020GL089455

Abstract: Using field, numerical, and laboratory studies, we consider the roles of both shear and convection in driving mixing in the interior of the density‐stratified ocean. Shear mixing dominates when the Richardson number Ri 0.25, convective mixing dominates when Ri 1.0, and in the intermediate regime when 0.25 Ri 1.0 both shear and convection can contribute to mixing. For pure shear mixing the mixing efficiency Ri f approaches 0.5, while for pure convective mixing the mixing efficiency Ri f approaches 0.75. The diapycnal diffusivities for the two mechanisms are given by very different expressions. Despite these complexities, a simple mixing length model using the mean flow shear S provides robust estimates of diffusivity across the range 0 Ri 2. To account for the roles of both shear and convection over this range of Ri , we also formulate a modified version of the empirical KPP model for parameterizing ocean mixing in numerical models.

Regimes and Transitions in the Basal Melting of Antarctic Ice Shelves

Publisher: American Meteorological Society

Date: 10-2022

DOI: 10.1175/JPO-D-21-0317.1

Abstract: The Antarctic Ice Sheet is losing mass as a result of increased ocean-driven melting of its fringing ice shelves. Efforts to represent the effects of basal melting in sea level projections are undermined by poor understanding of the turbulent ice shelf–ocean boundary layer (ISOBL), a meters-thick layer of ocean that regulates heat and salt transfer between the ocean and ice. To address this shortcoming, we perform large-eddy simulations of the ISOBL formed by a steady, geostrophic flow beneath horizontal ice. We investigate melting and ISOBL structure and properties over a range of free-stream velocities and ocean temperatures. We find that the melting response to changes in thermal and current forcing is highly nonlinear due to the effects of meltwater on ISOBL turbulence. Three distinct ISOBL regimes emerge depending on the relative strength of current shear and buoyancy forcing: “well-mixed,” “stratified,” or “diffusive-convective.” We present expressions for mixing-layer depth for each regime and show that the transitions between regimes can be predicted with simple nondimensional parameters. We use these results to develop a novel regime diagram for the ISOBL which provides insight into the varied melting responses expected around Antarctica and highlights the need to include stratified and diffusive-convective dynamics in future basal melting parameterizations. We emphasize that melting in the diffusive-convective regime is time dependent and is therefore inherently difficult to parameterize. The purpose of this study is to investigate the processes that control ocean-driven melting of Antarctic ice shelves (100–1000-m-thick floating extensions of the Antarctic ice sheet). Currently, these processes are poorly understood due to the difficulty of accessing the ocean beneath ice shelves. Using an ocean model, we determine the melting response to different ocean conditions, including feedbacks whereby cold, fresh meltwater can enhance or suppress turbulent eddies beneath the ice, depending on the ocean state. Our results point the way to improvements in the representation of ocean-driven melting in ocean/climate models, which will allow more accurate predictions of future climate and sea level.

Rotating Horizontal Convection

Publisher: Annual Reviews

Date: 05-01-2022

DOI: 10.1146/ANNUREV-FLUID-030121-115729

Abstract: Global differences of temperature and buoyancy flux at the ocean surface are responsible for small-scale convection at high latitudes, global overturning, and the top-to-bottom density difference in the oceans. With planetary rotation the convection also contributes to the large-scale horizontal, geostrophic circulation, and it crucially involves a 3D linkage between the geostrophic circulation and vertical overturning. The governing dynamics of such a surface-forced convective flow are fundamentally different from Rayleigh–Bénard convection, and the role of buoyancy forcing in the oceans is poorly understood. Geostrophic balance adds to the constraints on transport in horizontal convection, as illustrated by experiments, theoretical scaling, and turbulence-resolving simulations for closed (mid-latitude) basins and an annulus or reentrant zonal (circumpolar) channel. In these geometries, buoyancy drives either horizontal mid-latitude gyre recirculations or a strong Antarctic Circumpolar Current, respectively, in addition to overturning. At large Rayleigh numbers the release of available potential energy by convection leads to turbulent mixing with a mixing efficiency approaching unity. Turbulence-resolving models are also revealing the relative roles of wind stress and buoyancy when there is mixed forcing, and in future work they need to include the effects of turbulent mixing due to energy input from tides.

Evaporation induced convection enhances mixing in the upper ocean

Publisher: Frontiers Media SA

Date: 16-05-2023

DOI: 10.3389/FMARS.2023.1176226

Abstract: The upper ocean surface layer is directly affected by the air-sea fluxes. The diurnal variations in these fluxes also cause the upper ocean mixed layer turbulence and mixing to diurnally vary. The underlying thermohaline structure also varies accordingly throughout the day. Here we use large-eddy simulation to quantify the role of surface evaporation in modulating the diurnal mixed layer turbulence and mixing in the presence of wind forcing. During daytime, the upper ocean boundary layer becomes thermally stratified, and a salinity inversion layer is formed in the upper 10m, leading to double diffusive salt-fingering instability. During nighttime, the mixed layer undergoes convective deepening due to surface buoyancy loss redfrom both surface cooling and evaporation. We find that salinity makes a major contribution to the convective instability during both transitions between day and night. Overall surface evaporation increases the mixed layer depth and irreversible mixing through convection, both during nighttime and daytime, and leads to better prediction of the dynamical variables as sea surface salinity (SSS) and sea surface temperature (SST). Our findings can help improve the ocean parameterizations to improve the forecasts on a diurnal timescale.

Ocean Gyres Driven by Surface Buoyancy Forcing

Publisher: American Geophysical Union (AGU)

Date: 11-08-2020

DOI: 10.1029/2020GL088539

Abstract: Midlatitude gyres in the ocean are large‐scale horizontal circulations that are intensified on the western boundary of the ocean, giving rise to currents such as the Gulf Stream. The physical mechanism underlying gyres is widely recognized to involve the curl of the wind stress, which injects potential vorticity into the upper ocean. However, model results have highlighted the role of surface buoyancy fluxes (principally heating and cooling of the ocean surface) in driving circulation and enhancing gyre variability. Here we present two numerical simulations—one in the fully turbulent regime and the second an eddy‐permitting ocean model—which show that gyre‐like circulation can be driven by surface buoyancy fluxes alone. We explore this phenomenon through a combination of modeling and linear theory to highlight that the transport of ocean gyres depends upon surface buoyancy fluxes as well as wind stress.

Direct and large-eddy simulations of internal tide generation at a near-critical slope

Publisher: Cambridge University Press (CUP)

Date: 25-05-2011

DOI: 10.1017/JFM.2011.170

Abstract: A numerical study is performed to investigate nonlinear processes during internal wave generation by the oscillation of a background barotropic tide over a sloping bottom. The focus is on the near-critical case where the slope angle is equal to the natural internal wave propagation angle and, consequently, there is a resonant wave response that leads to an intense boundary flow. The resonant wave undergoes both convective and shear instabilities that lead to turbulence with a broad range of scales over the entire slope. A thermal bore is found during upslope flow. Spectra of the baroclinic velocity, both inside the boundary layer and in the external region with free wave propagation, exhibit discrete peaks at the fundamental tidal frequency, higher harmonics of the fundamental, subharmonics and inter-harmonics in addition to a significant continuous part. The internal wave flux and its distribution between the fundamental and harmonics is obtained. Turbulence statistics in the boundary layer including turbulent kinetic energy and dissipation rate are quantified. The slope length is varied with the smaller lengths examined by direct numerical simulation (DNS) and the larger with large-eddy simulation (LES). The peak value of the near-bottom velocity increases with the length of the critical region of the topography. The scaling law that is observed to link the near-bottom peak velocity to slope length is explained by an analytical boundary-layer solution that incorporates an empirically obtained turbulent viscosity. The slope length is also found to have a strong impact on quantities such as the wave energy flux, wave energy spectra, turbulent kinetic energy, turbulent production and turbulent dissipation.

Convection Enhances Mixing in the Southern Ocean

Publisher: American Geophysical Union (AGU)

Date: 11-05-2018

DOI: 10.1029/2018GL077711

Examining gender invariance of the Sport-Multidimensional Perfectionism Scale-2 in intercollegiate athletes

Publisher: Elsevier BV

Date: 2018

DOI: 10.1016/J.PSYCHSPORT.2017.09.005

Turbulent horizontal convection under spatially periodic forcing: A regime governed by interior inertia

Publisher: Cambridge University Press (CUP)

Date: 13-10-2017

DOI: 10.1017/JFM.2017.640

Abstract: Differential heating applied at a single horizontal boundary forces ‘horizontal convection’, even when there is no net heat flux through the boundary. However, almost all studies of horizontal convection have been limited to a special class of problem in which temperature or heat flux differences were applied in only one direction and over the horizontal length of a box (the Rossby problem Rossby, Deep-Sea Res. , vol. 12, 1965, pp. 9–16). These conditions strongly constrain the flow. Here we report laboratory experiments and direct numerical simulations (DNS) extending the results of Griffiths & Gayen ( Phys. Rev. Lett. , vol. 115, 2015, 204301) for horizontal convection forced by boundary conditions imposed in a two-dimensional periodic array at a horizontal boundary. The experiments use saline and freshwater fluxes at a permeable base with the imposed boundary salinity having a horizontal length scale one quarter of the width of the box. The flow reaches a state in which the net boundary buoyancy flux vanishes and the bulk of the fluid shows an inertial range of turbulence length scales. A regime transition is seen for increasing water depth, from an array of in idual coherent plumes on the forcing scale to convection dominated by emergent larger scales of overturning. The DNS explore the analogous thermally forced case with sinusoidal boundary temperature of wavenumber $n=4$ , and are used to examine the Rayleigh number ( $Ra$ ) dependence for shallow- and deep-water cases. For shallow water the flow transitions with increasing $Ra$ from laminar to turbulent boundary layer regimes that are familiar from the Rossby problem and which have normalised heat transport scaling as $Nu\\sim Ra^{1/5}$ and $Nu\\sim (Ra\\,Pr)^{1/5}$ , with $Nu$ the Nusselt number and $Pr$ the Prandtl number, in this case maintaining a stable array of coherent turbulent plumes. For deep-water and large $Ra$ the laminar scaling transitions to $Nu\\sim (Ra\\,Pr)^{1/4}$ , with the scales of turbulence extending to the dimensions of the box. The $1/4$ power law regime is explained in terms of the momentum of symmetric, inviscid large scales of motion in the interior coupled to diffusive loss of heat through stabilised parts of the boundary layer. The turbulence production is predominantly by shear instability rather than convection, with viscous dissipation distributed throughout the bulk of the fluid. These conditions are not seen in the highly asymmetric flow in the Rossby problem even at Rayleigh numbers up to six orders of magnitude greater than the transition found here. The new inertial interior regime has the rate of supply of available potential energy, and its removal by mixing of density, increasing as $Ra^{5/4}$ , which is faster than $Ra^{6/5}$ in the Rossby problem. Irreversible mixing is confined close to the forcing boundary and is very much larger than the viscous dissipation, which is proportional to $Ra$ .

Turbulence during the reflection of internal gravity waves at critical and near-critical slopes

Publisher: Cambridge University Press (CUP)

Date: 19-07-2013

DOI: 10.1017/JFM.2013.240

Abstract: Direct numerical simulation is performed with a focus on the characterization of nonlinear dynamics during reflection of a plane internal wave at a sloping bottom. The effect of incoming wave litude is assessed by varying the incoming Froude number, $Fr$ , and the effect of off-criticality is assessed by varying the slope angle in a range of near-critical values. At low $\\mathit{Fr}$ , the numerical results agree well with linear inviscid theory of near-critical internal wave reflection. With increasing $\\mathit{Fr}$ , the reflection process becomes nonlinear with the formation of higher harmonics and the initiation of fine-scale turbulence during the evolution of the reflected wave. Later in time, the wave response becomes quasi-steady with a systematic dependence of turbulence on the temporal and spatial phase. Convective instabilities are found to play a crucial role in the formation of turbulence during each cycle. The cycle evolution of flow statistics is studied in detail and qualitative differences between off-critical and critical reflection are identified. The parametric dependence of turbulence levels on Froude number and slope angle is calculated. Interestingly, at a given value of $\\mathit{Fr}$ , the turbulent kinetic energy (TKE) can be higher for somewhat off-critical reflection compared to exactly critical reflection. For a fixed slope angle, as the Froude number increases in the simulated cases, the fraction of the input wave energy converted into the turbulent kinetic energy and the fraction of the input wave power dissipated by turbulence also increase.

Peptide Programmed Hydrogels as Safe Sanctuary Microenvironments for Cell Transplantation

Publisher: Wiley

Date: 19-12-2019

DOI: 10.1002/ADFM.201900390

Eddy induced trapping and homogenization of freshwater in the Bay of Bengal

Publisher: Wiley

Date: 13-12-2021

DOI: 10.1002/ESSOAR.10509458.1

Topographic influence on submesoscale dynamics in the Southern Ocean

Publisher: American Geophysical Union (AGU)

Date: 24-02-2015

DOI: 10.1002/2014GL062720

Geostrophic and chimney regimes in rotating horizontal convection with imposed heat flux

Publisher: Cambridge University Press (CUP)

Date: 15-06-2017

DOI: 10.1017/JFM.2017.249

Abstract: Convection in a rotating rectangular basin with differential thermal forcing at one horizontal boundary is examined using laboratory experiments. The experiments have an imposed heat flux boundary condition, are at large values of the flux Rayleigh number ( $Ra_{F}\\sim O(10^{13}{-}10^{14})$ based on the box length $L$ ), use water with Prandtl number $Pr\\approx 4$ and have a small depth to length aspect ratio. The results show the conditions for transition from non-rotating horizontal convection governed by an inertial–buoyancy balance in the thermal boundary layer, to circulation governed by geostrophic flow in the boundary layer. The geostrophic balance constrains mean flow and reduces the heat transport as Nusselt number $Nu\\sim (Ra_{F}Ro)^{1/6}$ , where $Ro=B^{1/2}/f^{3/2}L$ is the convective Rossby number, $B$ is the imposed buoyancy flux and $f$ is the Coriolis parameter. Thus flow in the geostrophic boundary layer regime is governed by the relative roles of horizontal convective accelerations and Coriolis accelerations, or buoyancy and rotation, in the boundary layer. Experimental evidence suggests that for more rapid rotation there is another transition to a regime in which the momentum budget is dominated by fluctuating vertical accelerations in a region of vortical plumes, which we refer to as a ‘chimney’ following related discussion of regions of deep convection in the ocean. Coupling of the chimney convection in the region of destabilising boundary flux to the diffusive boundary layer of horizontal convection in the region of stabilising boundary flux gives heat transport independent of rotation in this ‘inertial chimney’ regime, and the new scaling $Nu\\sim Ra_{F}^{1/4}$ . Scaling analysis predicts the transition conditions observed in the experiments, as well as a further ‘geostrophic chimney’ regime in which the vertical plumes are controlled by local geostrophy. When $Ro ^{-1}$ , the convection is also observed to produce a set of large basin-scale gyres at all depths in the time-averaged flow.

Orientational correlation and velocity distributions in uniform shear flow of a dilute granular gas

Publisher: American Physical Society (APS)

Date: 14-02-2008

DOI: 10.1103/PHYSREVLETT.100.068002

Fundación EDP

Location: Spain

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Universidad De Oviedo

Location: Spain

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Universidad Nacional De Educación A Distancia

Location: Spain

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University Of Melbourne

Location: Australia

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University Of California, San Diego

Location: United States of America

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University Of British Columbia

Location: Canada

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Australian National University

Location: Australia

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University Of Massachusetts Amherst UMass Extension

Location: United States of America

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CTIC Centro Tecnológico

Location: Spain

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FeelIn Psicología Deportiva

Location: Spain

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Formador Especializado

Location: Spain

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Melbourne Institute, University Of Melbourne

Location: No location found

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Melbourne Institute, University Of Melbourne

Location: Australia

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Jawaharlal Nehru Centre For Advanced Scientific Research

Location: India

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Jadavpur University

Location: India

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Indian Institute Of Science Bangalore

Location: India

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A Facility To Produce And Quantify Accelerated Flow Mixing At High Fidelity

Start Date: 2023

End Date: 2024

Funder: Australian Research Council

Interactions Of Physical Processes For Southern Ocean Dynamics

Start Date: 2014

End Date: 2016

Funder: Australian Research Council

Spanning Ten Billion Scales From Millimetre Turbulence To Global Circulation

Start Date: 2018

End Date: 2021

Funder: Australian Research Council

Antarctic Ice Melting

Start Date: 2014

End Date: 2016

Funder: Australian Research Council

Australian Centre For Excellence In Antarctic Science

Start Date: 2021

End Date: 2024

Funder: Australian Research Council

Connecting Big Data With High Performance Computing For Climate Science

Start Date: 2015

End Date: 2015

Funder: Australian Research Council

Discovery Early Career Researcher Award - Grant ID: DE140100089

Start Date: 03-2014

End Date: 10-2017

Amount: $371,151.00

Funder: Australian Research Council

ARC Future Fellowships - Grant ID: FT180100037

Start Date: 07-2019

End Date: 05-2024

Amount: $695,125.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP140103706

Start Date: 2014

End Date: 12-2017

Amount: $405,000.00

Funder: Australian Research Council

Special Research Initiatives - Grant ID: SR200100008

Start Date: 08-2021

End Date: 12-2027

Amount: $20,000,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE220100132

Start Date: 2023

End Date: 12-2024

Amount: $660,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE150100089

Start Date: 2015

End Date: 12-2015

Amount: $490,000.00

Funder: Australian Research Council