Nicole L Jones

15 priorities for wind-waves research: An Australian perspective

Publisher: American Meteorological Society

Date: 04-2020

DOI: 10.1175/BAMS-D-18-0262.1

Abstract: The Australian marine research, industry, and stakeholder community has recently undertaken an extensive collaborative process to identify the highest national priorities for wind-waves research. This was undertaken under the auspices of the Forum for Operational Oceanography Surface Waves Working Group. The main steps in the process were first, soliciting possible research questions from the community via an online survey second, reviewing the questions at a face-to-face workshop and third, online ranking of the research questions by in iduals. This process resulted in 15 identified priorities, covering research activities and the development of infrastructure. The top five priorities are 1) enhanced and updated nearshore and coastal bathymetry 2) improved understanding of extreme sea states 3) maintain and enhance the in situ buoy network 4) improved data access and sharing and 5) ensemble and probabilistic wave modeling and forecasting. In this paper, each of the 15 priorities is discussed in detail, providing insight into why each priority is important, and the current state of the art, both nationally and internationally, where relevant. While this process has been driven by Australian needs, it is likely that the results will be relevant to other marine-focused nations.

Particle capture by a circular cylinder in the vortex-shedding regime

Publisher: Cambridge University Press (CUP)

Date: 19-09-2013

DOI: 10.1017/JFM.2013.407

Abstract: Particle capture, whereby suspended particles contact and adhere to a solid surface (a ‘collector’), is an important mechanism for a range of environmental processes including suspension feeding by corals and ‘filtering’ by aquatic vegetation. In this paper, we use two- and three-dimensional direct numerical simulations to quantify the capture efficiency ( $\\eta $ ) of low-inertia particles by a circular cylindrical collector at intermediate Reynolds numbers in the vortex-shedding regime (i.e. for $47\\lt \\mathit{Re}\\leq 1000$ , where $\\mathit{Re}$ is the collector Reynolds number). We demonstrate that vortex shedding induces oscillations near the leading face of the collector which greatly affect the quantity and distribution of captured particles. Unlike in steady, low- $\\mathit{Re}$ flow, particles directly upstream of the collector are not the most likely to be captured. Our results demonstrate the dependence of the time-averaged capture efficiency on $\\mathit{Re}$ and particle size, improving the predictive capability for the capture of particles by aquatic collectors. The transition to theoretical high-Reynolds-number behaviour (i.e. $\\eta \\sim {\\mathit{Re}}^{1/ 2} $ ) is complex due to comparatively rapid changes in wake conditions in this Reynolds number range.

Wave-current interactions in the continental shelf bottom boundary layer of the Australian North West Shelf during tropical cyclone conditions

Publisher: Elsevier BV

Date: 08-2018

DOI: 10.1016/J.CSR.2018.07.006

Internal tide dynamics in a topographically complex region: Browse Basin, Australian North West Shelf

Publisher: American Geophysical Union (AGU)

Date: 26-01-2011

DOI: 10.1029/2009JC005881

Nutrient fluxes into an isolated coral reef atoll by tidally driven internal bores

Publisher: Wiley

Date: 26-10-2018

DOI: 10.1002/LNO.11051

Dynamics of the summer shelf circulation and transient upwelling off Ningaloo Reef, Western Australia

Publisher: American Geophysical Union (AGU)

Date: 03-2013

DOI: 10.1002/JGRC.20098

Particle capture and low-Reynolds-number flow around a circular cylinder

Publisher: Cambridge University Press (CUP)

Date: 07-09-2012

DOI: 10.1017/JFM.2012.367

Abstract: Particle capture, whereby suspended particles contact and adhere to a solid surface (a ‘collector’), is an important mechanism in a range of environmental processes. In aquatic systems, typically characterized by low collector Reynolds numbers ( $\\mathit{Re}$ ), the rate of particle capture determines the efficiencies of a range of processes such as seagrass pollination, suspension feeding by corals and larval settlement. In this paper, we use direct numerical simulation (DNS) of a two-dimensional laminar flow to accurately quantify the rate of capture of low-inertia particles by a cylindrical collector for $\\mathit{Re}\\leq 47$ (i.e. a range where there is no vortex shedding). We investigate the dependence of both the capture rate and maximum capture angle on both the collector Reynolds number and the ratio of particle size to collector size. The inner asymptotic expansion of Skinner ( Q. J. Mech. Appl. Maths , vol. 28, 1975, pp. 333–340) for flow around a cylinder is extended and shown to provide an excellent framework for the prediction of particle capture and flow close to the leading face of a cylinder up to $\\mathit{Re}= 10$ . Our results fill a gap between theory and experiment by providing, for the first time, predictive capability for particle capture by aquatic collectors in a wide (and relevant) Reynolds number and particle size range.

Observations of Enhanced Sediment Transport by Nonlinear Internal Waves

Publisher: American Geophysical Union (AGU)

Date: 06-10-2020

DOI: 10.1029/2020GL088499

Turbulent mixing efficiency at an energetic ocean site

Publisher: American Geophysical Union (AGU)

Date: 09-2013

DOI: 10.1002/JGRC.20292

Observations of Diurnal Coastal-Trapped Waves with a Thermocline-Intensified Velocity Field

Publisher: American Meteorological Society

Date: 07-2019

DOI: 10.1175/JPO-D-18-0194.1

Abstract: Using 18 days of field observations, we investigate the diurnal (D1) frequency wave dynamics on the Tasmanian eastern continental shelf. At this latitude, the D1 frequency is subinertial and separable from the highly energetic near-inertial motion. We use a linear coastal-trapped wave (CTW) solution with the observed background current, stratification, and shelf bathymetry to determine the modal structure of the first three resonant CTWs. We associate the observed D1 velocity with a superimposed mode-zero and mode-one CTW, with mode one dominating mode zero. Both the observed and mode-one D1 velocity was intensified near the thermocline, with stronger velocities occurring when the thermocline stratification was stronger and/or the thermocline was deeper (up to the shelfbreak depth). The CTW modal structure and litude varied with the background stratification and alongshore current, with no spring–neap relationship evident for the observed 18 days. Within the surface and bottom Ekman layers on the shelf, the observed velocity phase changed in the cross-shelf and/or vertical directions, inconsistent with an alongshore propagating CTW. In the near-surface and near-bottom regions, the linear CTW solution also did not match the observed velocity, particularly within the bottom Ekman layer. Boundary layer processes were likely causing this observed inconsistency with linear CTW theory. As linear CTW solutions have an idealized representation of boundary dynamics, they should be cautiously applied on the shelf.

The geography of semidiurnal mode-1 internal-tide energy loss

Publisher: American Geophysical Union (AGU)

Date: 05-09-2013

DOI: 10.1002/GRL.50872

Observations of Multiple Internal Wave Packets in a Tidal River Plume

Publisher: American Geophysical Union (AGU)

Date: 27-07-2021

DOI: 10.1029/2020JC016575

Abstract: Remotely sensed images document the occurrence of multiple packets of internal solitary waves (ISWs) in the Rhine River plume at the same time. We use a combination of field observations, and non‐hydrostatic and hydrostatic modeling to understand the processes that lead to the generation and retention of multiple ISW packets within the Rhine plume. Previous numerical modeling shows that the tidal plume front is trapped in the mid‐field plume for more than one tidal cycle due to tidal straining and recirculation within the plume, resulting in the presence of multiple fronts in the near‐and mid‐field plume regions. In this work, we show how variations in the strength of these fronts can lead to the release of ISW packets. We conclude that the retention of the fronts in the mid‐field region of the plume and modulation in the strength of the fronts can explain the presence of multiple ISW packets. A frontal Froude number analysis shows that fronts generated during the previous ebb tide can release ISWs in addition to the newly released tidal plume front.

Experiments on the generation of internal waves over continental shelf topography

Publisher: Cambridge University Press (CUP)

Date: 08-09-2010

DOI: 10.1017/S002211201000354X

Abstract: Experiments were performed to examine the generation of internal waves by a barotropic tide forcing a continuously stratified fluid over idealized continental shelf/slope topography. A range of responses was observed, including the generation of both internal wave beams and boundary layer boluses, primarily dependent on the values of both the Reynolds number and the topographic steepness parameter. The formation of beams required a critical bottom slope, whilst for bolus formation a large vertical fluid excursion was necessary. A bolus formed when the non-dimensional vertical excursion parameter Δ hN / W 0 3.2. Here Δ h is the vertical excursion, N is the buoyancy frequency and W 0 is the near-bottom vertical velocity associated with the local depth-averaged velocity. We simplified the classification of the observed flow regimes using a generation parameter G , defined as the ratio of a Reynolds number to the topographic steepness parameter. The estimated flow regime boundaries were: for G 3 only a beam was observed, for 3 G 50 there was a transitional regime with both a beam and a bolus observed, for 50 G 400 there was another transitional regime with no beam but a bolus observed, and finally for the regime with G 400 there was no bolus observed. We estimated that approximately 4% of the barotropic energy was converted to baroclinic energy when beams were generated.

Ocean Transport Pathways to a World Heritage Fringing Coral Reef: Ningaloo Reef, Western Australia

Publisher: Public Library of Science (PLoS)

Date: 20-01-2016

DOI: 10.1371/JOURNAL.PONE.0145822

Ocean mixing in a shelf sea driven by energetic internal waves

Publisher: Authorea, Inc.

Date: 09-02-2023

DOI: 10.22541/ESSOAR.167591065.55629421/V1

Abstract: We collected observations of ocean mixing from three moorings placed at the 330m, 200m, and 150m isobaths on a pelagic ridge on the Australian North West Shelf (NWS). The region is subject to energetic surface and internal tides, non-linear internal waves, flow-topography interactions, and episodic intense wind events (i.e., tropical cyclones) that collectively drive energetic diapycnal mixing. We identified five dominant internal wave categories: both low (time scales from double the buoyancy period to 4 hours) and high-frequency (time scales between buoyancy period and double the buoyancy period) mode-1 waves, mode-2 waves, internal bores, and internal hydraulic jumps. A small number of turbulent mixing events dominated the total vertical heat flux at each mooring, with 15% of estimates accounting for as much as 90% of the total observed heat flux. These turbulent mixing events often occurred during the passage of internal wave events, with the internal wave events accounting for as much as 60% of the total heat flux in some locations. High-frequency mode-1 waves were the most significant contributors to the total vertical heat flux (∼ 20%). Internal bores made significant but localized contributions to mixing, accounting for up to ∼ 50% of the total vertical heat flux in some regions but with a negligible influence elsewhere. The contributions of the different internal wave categories to the total flux became more heterogeneous at shallower sites, indicating an increasingly complicated relationship between the forcing internal wave field and the mixing.

Evaluation of AUV-based ADCP measurements

Publisher: Wiley

Date: 03-2006

DOI: 10.4319/LOM.2006.4.58

A seasonal harmonic model for internal tide amplitude prediction

Publisher: Wiley

Date: 26-05-2021

DOI: 10.1002/ESSOAR.10507151.1

Calibrated Suspended Sediment Observations Beneath Large Amplitude Non‐Linear Internal Waves

Publisher: American Geophysical Union (AGU)

Date: 12-2021

DOI: 10.1029/2021JC017538

Abstract: While it has been recognized for some time that large litude non‐linear internal waves (NLIW) can mobilize and transport sediment, quantitative observations of this process are rare. Rarer still are accompanying estimates of suspended sediment mass concentration (SSC) during the passage of NLIW. Here, we present high resolution observations of NLIW and the SSC response within the bottom boundary layer. The observations were made in 250 m of water in a mildly sloping region of the Browse Basin on Australia’s Northwest Shelf. We compare two independent but direct calibration methods, and employ Bayesian methods to estimate the uncertainty in SSC. During a large NLIW event, the peak mean SSC estimate at 0.49 m above the sea bed was 161 mg L −1 , with a maximum time‐rate‐of‐change of 0.14 mg L −1 s −1 . The unsteady boundary layer forcing under NLIW resulted in a variable time‐height dependent relationship between bed stress and SSC with increasing height above the sea bed. Suspended sediment was restricted to the bottom mixing layer, with sharp vertical gradients of up to 40 mg L −1 m −1 observed at the edge of the layer. The observations presented here are intended to offer guidance to numerical sediment modelers about likely SSC under strong NLIW.

Determining Mixing Rates from Concurrent Temperature and Velocity Measurements

Publisher: American Meteorological Society

Date: 10-2017

DOI: 10.1175/JTECH-D-16-0250.1

Abstract: Ocean mixing has historically been estimated using Osborn’s model by measuring the rate of dissipation of turbulent kinetic energy ϵ and the background density stratification N while assuming a value of the flux Richardson number . A constant is typically assumed, despite mounting field, laboratory, and modeling evidence that varies. This challenge can be overcome by estimating the turbulent diffusivity of heat using the Osborn–Cox model. This model, however, requires measuring the rate of dissipation of thermal variance χ , which has historically been challenging, particularly in energetic flows because the high wavenumbers of the temperature gradient spectra are unresolved with current technology. To overcome this difficulty, a method is described that determines χ by spectral fitting to the inertial-convective (IC) subrange of the temperature gradient spectra. While this concept has been exploited for moored time series, particularly near the bottom boundary, it has yet to be adapted to vertical microstructure profilers such as gliders, and autonomous and ship-based vertical profilers from which there are the most measurements. By using the IC subrange, χ , and hence , can be estimated even in very energetic events—precisely the conditions requiring more field observations. During less energetic periods, the temperature gradient spectra can also be integrated to obtain χ . By combining these two techniques, microstrucure profiles at a field site known for its very energetic internal waves are analyzed. This study demonstrates that the spectral fitting approach resolves intense mixing events with . By equating the Osborn and Osborn–Cox models, indirect estimates for can also be obtained.

Modeling the influence of wave-enhanced turbulence in a shallow tide- and wind-driven water column

Publisher: American Geophysical Union (AGU)

Date: 03-2008

DOI: 10.1029/2007JC004246

Observations of Large-Amplitude Mode-2 Nonlinear Internal Waves on the Australian North West Shelf

Publisher: American Meteorological Society

Date: 2019

DOI: 10.1175/JPO-D-18-0097.1

Abstract: Large- litude mode-2 nonlinear internal waves were observed in 250-m-deep water on the Australian North West shelf. Wave litudes were derived from temperature measurements using three through-the-water-column moorings spaced 600 m apart in a triangular configuration. The moorings were deployed for 2 months during the transition period between the tropical monsoon and the dry season. The site had a 25–30-m- litude mode-1 internal tide that essentially followed the spring–neap tidal cycle. Regular mode-2 nonlinear wave trains with litudes exceeding 25 m, with the largest event exceeding 50 m, were also observed at the site. Overturning was observed during several mode-2 events, and the relatively high wave Froude number and steepness (0.15) suggested kinematic (convective) instability was likely to be the driving mechanism. The presence of the mode-2 waves was not correlated with the tidal forcing but rather occurred when the nonlinear steepening length scale was smaller than the distance from the generation region to the observation site. This steepening length scale is inversely proportional to the nonlinear parameter in the Korteweg–de Vries equation, and it varied by at least one order of magnitude under the evolving background thermal stratification over the observation period. Despite the complexity of the internal waves in the region, the nonlinear steepening length was shown to be a reliable indicator for the formation of large- litude mode-2 waves and the rarer occurrence of mode-1 large- litude waves. A local mode-2 generation mechanism caused by a beam interacting with a pycnocline is demonstrated using a fully nonlinear numerical solution.

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.

Deposition and Fate of Arsenic in Iron- and Arsenic-Enriched Reservoir Sediments

Publisher: American Chemical Society (ACS)

Date: 04-01-2002

DOI: 10.1021/ES010922H

Abstract: Deposition of arsenic to the sediments of Haiwee Reservoir (Olancha, CA) has dramatically increased since March 1996 as a result of an interim strategy for arsenic management in the Los Angeles Aqueduct (LAA) water supply. Ferric chloride and cationic polymer are introduced into the Aqueduct at the Cottonwood treatment plant, 27 km north of the Haiwee Reservoir. This treatment decreases the average arsenic concentration from 25 microg/L above Cottonwood to 8.3 microg/L below Haiwee. Iron- and arsenic-rich flocculated solids are removed by deposition to the reservoir sediments. Analysis of sediments shows a pronounced signature of this deposition with elevated sediment concentrations of iron, arsenic, and manganese relative to a control site. Sediment concentrations of these elements remain elevated throughout the core length s led (ca. 4% iron and 600 and 200 microg/g of manganese and arsenic, respectively, on a dry weight basis). A pore water profile revealed a strong redox gradient in the sediment. Manganese in the pore waters increased below 5 cm iron and arsenic increased below 10 cm and were strongly correlated, consistent with reductive dissolution of iron oxyhydroxides and concurrent release of associated arsenic to solution. X-ray absorption near-edge spectroscopy revealed inorganic As(V) present only in the uppermost sediment (0-2.5 cm) in addition to inorganic As(III). In the deeper sediments (to 44 cm), only oxygen-coordinated As(III) was detected. Analysis of the extended X-ray absorption fine structure spectrum indicates that the As(III) at depth remains associated with iron oxyhydroxide. We hypothesize that this phase persists in the recently deposited sediment despite reducing conditions due to slow dissolution kinetics.

Modeling bed shear-stress fluctuations in a shallow tidal channel

Publisher: American Geophysical Union (AGU)

Date: 05-2014

DOI: 10.1002/2013JC009718

In-situ estimation of erosion model parameters using an advection-diffusion model and Bayesian inversion

Publisher: Wiley

Date: 16-11-2022

DOI: 10.1002/ESSOAR.10512841.1

Temporal variability of the standing internal tide in the Browse Basin, Western Australia

Publisher: American Geophysical Union (AGU)

Date: 06-2012

DOI: 10.1029/2011JC007523

A Seasonal Harmonic Model for Internal Tide Amplitude Prediction

Publisher: American Geophysical Union (AGU)

Date: 10-2021

DOI: 10.1029/2021JC017570

Abstract: We present an empirical model of the seasonal variability of the internal tide using seasonal harmonics to modulate the litude of the fundamental tidal constituents. Internal tide data, from both long‐term, in‐situ moorings and a mesoscale‐resolving and internal tide‐resolving ocean model, are used to demonstrate the performance of the seasonal harmonic model for the Indo‐Australian Basin region. The seasonal model describes up to 15% more of the observed (baroclinic) sea surface height variance than a fixed‐ litude harmonic model at the mooring sites. The ocean model results demonstrate that the study region, which includes the Australian North West Shelf (NWS), Timor Sea, and southern Indonesian Islands, is dominated by standing wave interference patterns due to the presence of multiple generation sites. The seasonal harmonic model reveals that temporal shifts in the standing wave patterns coincide with seasonal variations in density stratification. This shift is particularly evident within distances of 2–3 internal wave lengths from strong generation sites. The fraction of the variance of the internal tide signal explained by seasonal modulations is largest in standing wave node regions, contributing to differences in predictive skill of the seasonal harmonic model at two moorings separated by only 38 km. Output of the harmonic model also demonstrates that the seasonally evolving internal tide propagating southward from Lombok Strait had a small litude in October when shear from the Indonesian Throughflow was strongest.

Directional decomposition of internal tides propagating from multiple generation sites

Publisher: Elsevier BV

Date: 06-2021

DOI: 10.1016/J.OCEMOD.2021.101801

The Effects of Remote Internal Tides on Continental Slope Internal Tide Generation

Publisher: American Meteorological Society

Date: 06-2019

DOI: 10.1175/JPO-D-18-0180.1

Abstract: Internal tide generation at sloping topography is nominally determined by the local slope geometry, density stratification, and tidal forcing. Recent global ocean models have revealed that remotely generated internal tides (RITs) can also influence locally generated internal tides (LITs). Field measurements with through-the-water column moorings on the southern portion of the Australian North West Shelf (NWS) suggested that RITs led to local regions with either positive or negative barotropic to baroclinic energy conversion. Three-dimensional numerical simulations were used to examine the role of RITs on local internal tide climatology on the inner slope and shelf portion of the NWS. The model demonstrated the principle remote generation site was the western portion of the offshore Exmouth Plateau. Extending the model domain to include this offshore plateau region increased the local net energy conversion on the inner shelf by 13.5% and on the slope by 8%. Simulations using an idealized 2D model configuration aligned along the principal direction of RIT propagation demonstrated that the sign and magnitude of the local energy conversion was dependent on the distance between the remote and local generation sites, the phase difference between the local barotropic tide and the RIT, and the litude of both the local barotropic tide and the RIT. For RITs with a low-wave Froude number (Fr 0.05), where Fr is the ratio of the internal wave baroclinic velocity to the linear wave speed, the conversion rates were consistent with kinematic predictions based on the phase difference only. For stronger flows with Fr 0.05, the conversion rates showed a nonlinear dependence on Fr.

The influence of whitecapping waves on the vertical structure of turbulence in a shallow estuarine embayment

Publisher: American Meteorological Society

Date: 07-2008

DOI: 10.1175/2007JPO3766.1

Abstract: The vertical distribution of the turbulent kinetic energy dissipation rate was measured using an array of four acoustic Doppler velocimeters in the shallow embayment of Grizzly Bay, San Francisco Bay, California. Owing to the combination of wind and tide forcing in this shallow system, the surface and bottom boundary layers overlapped. Whitecapping waves were generated for a significant spectral peak steepness greater than 0.05 or above a wind speed of 3 m s−1. Under conditions of whitecapping waves, the turbulent kinetic energy dissipation rate in the upper portion of the water column was greatly enhanced, relative to the predictions of wind stress wall-layer theory. Instead, the dissipation followed a modified deep-water breaking-wave scaling. Near the bed (bottom 10% of the water column), the dissipation measurements were either equal to or less than that predicted by wall-layer theory. Stratification due to concentration gradients in suspended sediment was identified as the likely cause for these periods of production–dissipation imbalance close to the bed. During 50% of the well-mixed conditions experienced in the month-long experiment, whitecapping waves provided the dominant source of turbulent kinetic energy over 90% or more of the water column.

Hydrodynamic control of phytoplankton loss to the benthos in an estuarine environment

Publisher: Wiley

Date: 05-2009

DOI: 10.4319/LO.2009.54.3.0952

Density-ratio effects on the capture of suspended particles in aquatic systems

Publisher: Cambridge University Press (CUP)

Date: 15-10-2015

DOI: 10.1017/JFM.2015.557

Abstract: Particle capture, whereby suspended particles contact and adhere to a solid surface (a ‘collector’), is important in a range of environmental processes, including suspension feeding by corals and ‘filtering’ by aquatic vegetation. Although aquatic particles are often considered as perfect tracers when estimating capture efficiency, the particle density ratio ( ${\\it\\rho}^{+}$ ) – the ratio of the particle density to the fluid density – can significantly affect capture. In this paper, we use a numerical analysis of particle trajectories to quantify the influence of ${\\it\\rho}^{+}$ on particle capture by circular collectors in a parameter space relevant to aquatic systems. As it is generally believed that inertia augments the capture efficiency when the Stokes number ( $\\mathit{St}$ ) of the particles exceeds a critical value, we first estimate the critical Stokes number for aquatic-type particles and demonstrate its dependence on both ${\\it\\rho}^{+}$ and the Reynolds number ( $\\mathit{Re}$ ). Second, we analyse how efficiently circular collectors can capture neutrally buoyant ( ${\\it\\rho}^{+}=1$ ), sediment-type ( ${\\it\\rho}^{+}=2.6$ ) and weakly buoyant ( ${\\it\\rho}^{+}=0.9$ ) aquatic particles. Our analysis shows that, for ${\\it\\rho}^{+} $ , inertia can either augment or diminish capture efficiency, and inertial effects appear well before the critical Stokes number is reached. The role of particle inertia is maximised at Stokes numbers above the critical value and, for sediment-type particles, can result in as much as a fourfold increase in the rate of capture relative to perfect tracers of the same size. Similar but opposite effects are observed for weakly buoyant particles, where capture efficiency can decrease by 60 % relative to the capture of perfect tracers.

Quantifying Diapycnal Mixing in an Energetic Ocean

Publisher: American Geophysical Union (AGU)

Date: 2018

DOI: 10.1002/2017JC013242

Reconstruction of Wall Shear-Stress Fluctuations in a Shallow Tidal River

Publisher: Springer International Publishing

Date: 18-08-2015

DOI: 10.1007/978-3-319-20388-1_22

The effects of tropical cyclone characteristics on the surface wave fields in Australia's North West region

Publisher: Elsevier BV

Date: 05-2017

DOI: 10.1016/J.CSR.2017.03.006

Contrasting Heat Budget Dynamics During Two La Niña Marine Heat Wave Events Along Northwestern Australia

Publisher: American Geophysical Union (AGU)

Date: 02-2018

DOI: 10.1002/2017JC013426

Local winds and encroaching currents drive summertime subsurface blooms over a narrow shelf

Publisher: Wiley

Date: 24-02-2022

DOI: 10.1002/LNO.12043

Abstract: The ability to forecast the biological productivity of the coastal ocean relies on the quantification of the physical processes that deliver nutrients to the euphotic zone. Here we explore these pathways using observations of the coupled biological and physical variability of waters offshore of the east coast of Tasmania in the summertime. The observations include an array of moored autonomous profilers deployed over an 18‐d period—providing continuous, full‐depth measurements of turbulent microstructure, temperature, velocity, and chlorophyll a (Chl a ) fluorescence, complemented by shipboard nutrient measurements. Local upwelling was driven by the encroaching East Australian Current (EAC) extension onto the shelf and to a lesser extent the local winds. The interaction of the local winds and the encroaching boundary current was reflected in the shelf nutrient budget and led to a rapid increase in subsurface Chl a . Diffusive vertical fluxes had minimal impact on subsurface Chl a in the mid‐shelf and outer‐shelf. Upwelling‐favorable winds were too weak to drive significant vertical mixing, and mixing associated with the current‐driven Ekman transport was too deep compared to the euphotic zone depth. The observed subsurface Chl a did not reflect the satellite estimates of productivity. Since the EAC extension transports warm, low‐nutrient surface waters from the subtropics, satellite chlorophyll measurements decreased during the same period the depth‐averaged Chl a increased. This seeming paradox illustrated how long duration, full water column s ling can elucidate the coupled biological and physical processes that aid our ongoing effort to forecast the biological state of the coastal ocean.

Are any coastal internal tides predictable?

Publisher: The Oceanography Society

Date: 06-2012

DOI: 10.5670/OCEANOG.2012.44

Internal Waves

Publisher: Wiley

Date: 20-04-2017

DOI: 10.1002/9781118476406.EMOE089

Abstract: Internal waves are a ubiquitous feature in the ocean. They are of considerable importance in the marine environment as they can both create currents and drive turbulent ocean mixing. Nonlinear internal waves (NLIWs) or solitons induce large vertical displacements of constant density (isopycnal) surfaces of O(100 m) and strong horizontal velocities of O(1–2 m/s) as they propagate. Such large displacements and velocities, in turn, affect nutrient mixing and biological productivity, sediment resuspension, the propagation of acoustic waves, and marine and offshore engineering operations. As NLIWs are potentially hazardous to subsea oil and gas operations, the ability to predict the occurrence and arrival of these waves is necessary for both cost‐effective operation and safety. Despite the considerable body of knowledge about these waves, the prediction of NLIWs remains a very challenging issue and the subject of ongoing research. This article first discusses the theory of internal waves. It then focuses on the generation, propagation, and dissipation of internal tides. Finally, it considers the implications of internal tide dynamics for engineering design and operation in the offshore environment.

Data Availability Principles and Practice

Publisher: American Meteorological Society

Date: 12-2020

DOI: 10.1175/JPO-D-20-0266.1

Dynamics of a tidally‐forced stratified shear flow on the continental slope

Publisher: American Geophysical Union (AGU)

Date: 11-2011

DOI: 10.1029/2011JC007214

Abstract: The near seabed mean and turbulent processes on the continental slope were measured for a three week period using an array of acoustic‐Doppler velocimeters and thermistors over the bottom 30 m at the 400 m isobath. Baroclinic motions with characteristics similar to internal bores or boluses propagated onshore during the flood phase of both spring and neap tides. The arrival time of these internal bores at our measurement site varied amongst tidal cycles and their characteristics were not highly correlated with the litude of the barotropic tidal forcing. The passage of the internal bores was associated with large turbulent overturns, enhanced turbulent kinetic energy dissipation (ε 10 −6 W kg −1 ) and intensified currents ( times the barotropic forcing) within meters of the seabed. During the deployment, stratification and shear competed to govern our observed overturning length scale (≲4 m) that were characterized by the Ellison length scale L E . Only measurements closest to the seabed (1.7 m) were described by the log law‐of‐the‐wall generally both buoyancy and the presence of the bottom boundary influenced L E , while sometimes flow‐induced shear determined L E . As the distance of our measurements from the seabed increased, the influence of buoyancy became more pronounced. These results highlight that a more general descriptor of the overturning length scale is necessary for complex stratified shear flows.

Generation and Propagation of Near-Inertial Waves in a Baroclinic Current on the Tasmanian Shelf

Publisher: American Meteorological Society

Date: 10-2019

DOI: 10.1175/JPO-D-18-0208.1

Abstract: Near-inertial waves (NIWs) are often an energetic component of the internal wave field on windy continental shelves. The effect of baroclinic geostrophic currents, which introduce both relative vorticity and baroclinicity, on NIWs is not well understood. Relative vorticity affects the resonant frequency f eff , while both relative vorticity and baroclinicity modify the minimum wave frequency of freely propagating waves ω min . On a windy and narrow shelf, we observed wind-forced oscillations that generated NIWs where f eff was less than the Coriolis frequency f . If everywhere f eff f then NIWs were generated where ω min f and f eff was smallest. The background current not only affected the location of generation, but also the NIWs’ propagation direction. The estimated NIW energy fluxes show that NIWs propagated predominantly toward the equator because ω min f on the continental slope for the entire s le period. In addition to being laterally trapped on the shelf, we observed vertically trapped and intensified NIWs that had a frequency ω within the anomalously low-frequency band (i.e., ω min ω f eff ), which only exists if the baroclinicity is nonzero. We observed two periods when ω min f on the shelf, but the relative vorticity was positive (i.e., f eff f ) for one of these periods. The process of NIW propagation remained consistent with the local ω min , and not f eff , emphasizing the importance of baroclinicity on the NIW dynamics. We conclude that windy shelves with baroclinic background currents are likely to have energetic NIWs, but the current and seabed will adjust the spatial distribution and energetics of these NIWs.

Seasonal circulation and temperature variability near the North West Cape of Australia

Publisher: American Geophysical Union (AGU)

Date: 04-2012

DOI: 10.1029/2011JC007653

Uncertainty Quantification of Density and Stratification Estimates with Implications for Predicting Ocean Dynamics

Publisher: American Meteorological Society

Date: 07-2019

DOI: 10.1175/JTECH-D-18-0200.1

Abstract: We present a statistical method for reconstructing continuous background density profiles that embeds incomplete measurements and a physically intuitive density stratification model within a Bayesian hierarchal framework. A double hyperbolic tangent function is used as a parametric density stratification model that captures various pycnocline structures in the upper ocean and offers insight into several density profile characteristics (e.g., pycnocline depth). The posterior distribution is used to quantify uncertainty and is estimated using recent advances in Markov chain Monte Carlo s ling. Temporally evolving posterior distributions of density profile characteristics, isopycnal heights, and nonlinear ocean process models for internal gravity waves are presented as ex les of how uncertainty propagates through models dependent on the density stratification. The results show 0.95 posterior interval widths that ranged from 2.5% to 4% of the expected values for the linear internal wave phase speed and 15%–40% for the nonlinear internal wave steepening parameter. The data, collected over a year from a through-the-column mooring, and code, implemented in the software package Stan, accompany the article.

A non-stationary harmonic model for seasonal internal tide amplitude prediction

Publisher: Wiley

Date: 20-11-2020

DOI: 10.1002/ESSOAR.10504834.1

In Situ Estimation of Erosion Model Parameters Using an Advection‐Diffusion Model and Bayesian Inversion

Publisher: American Geophysical Union (AGU)

Date: 06-2023

DOI: 10.1029/2022MS003500

Abstract: We describe a framework for the simultaneous estimation of model parameters in a partial differential equation using sparse observations. Markov Chain Monte Carlo s ling is used in a Bayesian framework to estimate posterior probability distributions for each parameter. We describe the necessary components of this approach and its broad potential for application in models of unsteady processes. The framework is applied to three case studies, of increasing complexity, from the field of cohesive sediment transport. We demonstrate that the framework can be used to recover posterior distributions for all parameters of interest and the results agree well with independent estimates (where available). We also demonstrate how the framework can be used to compare different model parameterizations and provide information on the covariance between model parameters.

Near‐inertial ocean response to tropical cyclone forcing on the Australian North‐West Shelf

Publisher: American Geophysical Union (AGU)

Date: 12-2015

DOI: 10.1002/2015JC010868

Measuring short-period wind waves in a tidally forced environment with a subsurface pressure gauge

Publisher: Wiley

Date: 10-2007

DOI: 10.4319/LOM.2007.5.317

Estimating Turbulent Dissipation from Microstructure Shear Measurements Using Maximum Likelihood Spectral Fitting over the Inertial and Viscous Subranges

Publisher: American Meteorological Society

Date: 04-2016

DOI: 10.1175/JTECH-D-15-0218.1

Abstract: A technique is presented to derive the dissipation of turbulent kinetic energy ϵ by using the maximum likelihood estimator (MLE) to fit a theoretical or known empirical model to turbulence shear spectral observations. The commonly used integration method relies on integrating the shear spectra in the viscous range, thus requiring the resolution of the highest wavenumbers of the turbulence shear spectrum. With current technology, the viscous range is not resolved at sufficiently large wavenumbers to estimate high ϵ however, long inertial subranges can be resolved, making spectral fitting over both this subrange and the resolved portion of the viscous range an attractive method for deriving ϵ . The MLE takes into account the chi-distributed properties of the spectral observations, and so it does not rely on the log-transformed spectral observations. This fitting technique can thus take advantage of both the inertial and viscous subranges, a portion of both, or simply one of the subranges. This flexibility allows a broad range of ϵ to be resolved. The estimated ϵ is insensitive to the range of wavenumbers fitted with the model, provided the noise-dominated portion of the spectra and the low wavenumbers impacted by the mean flow are avoided. For W kg −1 , the MLE fitting estimates agree with those obtained by integrating the spectral observations. However, with increasing ϵ the viscous subrange is not fully resolved and the integration method progressively starts to underestimate ϵ compared with the values obtained from fitting the spectral observations.

Mixing Driven by Breaking Nonlinear Internal Waves

Publisher: American Geophysical Union (AGU)

Date: 25-09-2020

DOI: 10.1029/2020GL089591

Estimating turbulent kinetic energy dissipation using the inertial subrange method in environmental flows

Publisher: Wiley

Date: 07-2011

DOI: 10.4319/LOM.2011.9.302

Observations of the shelf circulation dynamics along Ningaloo Reef, Western Australia during the austral spring and summer

Publisher: Elsevier BV

Date: 03-2015

DOI: 10.1016/J.CSR.2014.12.013

Generation and Propagation of Near-Inertial Waves in a Baroclinic Current on the Tasmanian Shelf

Publisher: No publisher found

DOI: 10.1175/JPO-D-18-0208.1}

Internal-Tide Spectroscopy and Prediction in the Timor Sea

Publisher: American Meteorological Society

Date: 2015

DOI: 10.1175/JPO-D-14-0007.1

Abstract: Spectral analyses of two 3.5-yr mooring records from the Timor Sea quantified the coherence of mode-0 (surface) and mode-1 (internal) tides with the astronomical tidal potential. The noncoherent tides had well-defined variance and were most accurately quantified for tidal species (as opposed to constituents) in long records ( months). On the continental slope (465 m), the semidiurnal mode-0 and mode-1 velocity and mode-1 pressure variance were 95%, 68%, and 56% coherent, respectively. On the continental shelf (145 m), the semidiurnal mode-0 and mode-1 velocity and mode-1 pressure variance were 98%, 34%, and 42% coherent, respectively. The response method produced time series of the semidiurnal coherent and noncoherent tides. The spectra and decorrelation time scales of the semidiurnal tidal litudes were similar to those of the barotropic mean flow and mode-1 eigenspeed (~4 days), suggesting local mesoscale variability shapes noncoherent tidal variability. Over long time scales ( days), mode-1 sea surface displacement litudes were positively correlated with mode-1 eigenspeed on the shelf. At both moorings, internal tides were likely modulated during both generation and propagation. Self-prediction using the response method enabled about 75% of semidiurnal mode-1 sea surface displacement to be predicted 2.5 days in advance. Improved prediction models will require realistic tide–topography coupling and background variability with both short and long time scales.

Acquiring Long-Term Turbulence Measurements from Moored Platforms Impacted by Motion

Publisher: American Meteorological Society

Date: 11-2016

DOI: 10.1175/JTECH-D-16-0041.1

Abstract: For measurements from either profiling or moored instruments, several processing techniques exist to estimate the dissipation rate of turbulent kinetic energy ϵ , a core quantity used to determine oceanic mixing rates. Moored velocimeters can provide long-term measurements of ϵ , but they can be plagued by motion-induced contamination. To remove this contamination, two methodologies are presented that use independent measurements of the instrument’s acceleration and rotation in space. The first is derived from the relationship between the spectra (cospectra) and the variance (covariance) of a time series. The cospectral technique recovers the environmental (or true) velocity spectrum by summing the measured spectrum, the motion-induced spectrum, and the cospectrum between the motion-induced and measured velocities. The second technique recovers the environmental spectrum by correcting the measured spectrum with the squared coherency, essentially assuming that the measured signal shares variance with either the environmental signal or the motion signal. Both techniques are applied to moored velocimeters at 7.5 and 20.5 m above the seabed in 105 m of water. By estimating the orbital velocities from their respective spectra and comparing them against those obtained from nearby wave measurements, the study shows that the surface wave signature is recovered with the cospectral technique, while it is underpredicted with the squared coherency technique. The latter technique is particularly problematic when the instrument’s motion is in phase with the orbital (environmental) velocities, as it removes variance that should have been added to the measured spectrum. The estimated ϵ from the cospectral technique compares well with estimates from nearby microstructure velocity shear vertical profiles.

Mean and Turbulent Characteristics of a Bottom Mixing‐Layer Forced by a Strong Surface Tide and Large Amplitude Internal Waves

Publisher: American Geophysical Union (AGU)

Date: 2022

DOI: 10.1029/2020JC017055

Abstract: We present 15 days of both mean and turbulent field observations bottom mixing‐layer at a gently sloping 250 m deep continental shelf site, energized by tides and nonlinear internal waves (NLIWs). The tidal frequency forcing was due to the combined effects of the barotropic tide and a mode‐1 internal tide (IT), while the NLIWs were predominantly mode‐1 waves of depression. The bottom mixing‐layer thickness varied at both semidiurnal and sub‐tidal ∼O(10)d frequencies, with an average thickness of around 10 m. Compression and expansion of the mixing‐layer by both the IT and NLIWs affected the mean velocity profiles in the mixing‐layer, while the phasing between the barotropic and baroclinic flows led to an asymmetry in mean velocity profiles between periods of rising and falling isotherms. With the exception of periods of flow reversal, the turbulent kinetic energy balance and turbulent stress observations were consistent with the existence of an inertial‐sublayer with thickness of approximately 10%–15% of the mixing‐layer thickness ( ∼1 m), even beneath NLIWs. In the outer portion of the mixing‐layer—that is, above the inertial‐sublayer—NLIWs modulated the local turbulence spectra. We discuss the observations in the context of a predictive model for mixing‐layer thickness. The analysis suggests that the high‐frequency variability in mixing‐layer thickness was dominated by internal wave pumping, though strength of the ambient stratification and the frequency of the forcing were important controls on the time‐averaged (sub‐tidal) variation.

Plume dispersion on a fringing coral reef system

Publisher: Wiley

Date: 09-2008

DOI: 10.4319/LO.2008.53.5_PART_2.2273

Impact of windage on ocean surface Lagrangian coherent structures

Publisher: Springer Science and Business Media LLC

Date: 16-12-2016

DOI: 10.1007/S10652-016-9499-3

4D-Var data assimilation using satellite sea surface temperature to improve the tidally-driven interior ocean dynamics in the Indo-Australian Basin

Publisher: Elsevier BV

Date: 03-2022

DOI: 10.1016/J.OCEMOD.2022.101969

Biophysical characteristics of a morphologically-complex macrotidal tropical coastal system during a dry season

Publisher: Elsevier BV

Date: 08-2014

DOI: 10.1016/J.ECSS.2014.07.018

Resolving high-frequency internal waves generated at an isolated coral atoll using an unstructured grid ocean model

Publisher: Elsevier BV

Date: 02-2018

DOI: 10.1016/J.OCEMOD.2017.12.007

A Coupled Model for Laplace's Tidal Equations in a Fluid with One Horizontal Dimension and Variable Depth

Publisher: American Meteorological Society

Date: 08-2013

DOI: 10.1175/JPO-D-12-0147.1

Abstract: Tide–topography interactions dominate the transfer of tidal energy from large to small scales. At present, it is poorly understood how low-mode internal tides reflect and scatter along the continental margins. Here, the coupling equations for linear tides model (CELT) are derived to determine the independent modal solutions to Laplace's Tidal Equations (LTE) over stepwise topography in one horizontal dimension. CELT is (i) applicable to arbitrary one-dimensional topography and realistic stratification without requiring numerically expensive simulations and (ii) formulated to quantify scattering because it implicitly separates incident and reflected waves. Energy fluxes and horizontal velocities obtained using CELT are shown to converge to analytical solutions, indicating that “flat bottom” modes, which evolve according to LTE, are also relevant in describing tides over sloping topography. The theoretical framework presented can then be used to quantify simultaneous incident and reflected energy fluxes in numerical simulations and observations of tidal flows that vary in one horizontal dimension. Thus, CELT can be used to diagnose internal-tide scattering on continental slopes. Here, semidiurnal mode-1 scattering is simulated on the Australian northwest, Brazil, and Oregon continental slopes. Energy-flux ergence and directional energy fluxes computed using CELT are shown to agree with results from a finite-volume model that is significantly more numerically expensive. Last, CELT is used to examine the dynamics of two-way surface–internal-tide coupling. Semidiurnal mode-1 internal tides are found to transmit about 5% of their incident energy flux to the surface tide where they impact the continental slope. It is hypothesized that this feedback may decrease the coherence of sea surface displacement on continental shelves.

University Of Western Australia

Location: Australia

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Discovery Projects - Grant ID: DP180101736

Start Date: 2018

End Date: 12-2022

Amount: $387,152.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP1095294

Start Date: 2010

End Date: 12-2013

Amount: $430,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP120103036

Start Date: 2012

End Date: 03-2016

Amount: $520,000.00

Funder: Australian Research Council

Industrial Transformation Research Hubs - Grant ID: IH140100012

Start Date: 04-2016

End Date: 12-2021

Amount: $4,997,672.00

Funder: Australian Research Council

Linkage Projects - Grant ID: LP110100017

Start Date: 10-2011

End Date: 11-2014

Amount: $559,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP210102745

Start Date: 2021

End Date: 12-2023

Amount: $772,031.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP140101322

Start Date: 2014

End Date: 06-2017

Amount: $466,600.00

Funder: Australian Research Council

Linkage Projects - Grant ID: LP210200613

Start Date: 04-2022

End Date: 04-2026

Amount: $707,971.00

Funder: Australian Research Council

Industrial Transformation Research Hubs - Grant ID: IH200100009

Start Date: 07-2021

End Date: 06-2026

Amount: $5,000,000.00

Funder: Australian Research Council