Jolimont, Australia
Jolimont, Australia

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Shimizu K.,RPS MetOcean Pty Ltd. | Shimizu K.,Kitami Institute of Technology | Shimizu K.,Max Planck Institute Fr Meteorologie
Journal of Geophysical Research: Oceans | Year: 2012

This study proposes new parameterizations of diapycnal mixing by reanalyzing the results of previous laboratory and numerical experiments on homogeneous stably stratified shear flows. Unlike previous studies that use either the turbulent Froude number Fr or gradient Richardson number Ri g, this study parameterizes nondimensional momentum and buoyancy fluxes as functions of Fr and a turbulent shear number Sh, in order to quantify individual effects of shear and stratification. Turbulent momentum flux is found to depend linearly on Sh and to decrease monotonically with decreasing Fr. Turbulent buoyancy flux has a peak at moderate Fr. With increasing Sh, it decreases and increases at high and low Fr, respectively. The increase of Sh also cause relatively small but significant decreases of nondimensional turbulent properties, such as the nondimensional conversion rate of turbulent potential energy to background potential energy. The proposed parameterizations lie within the scatter of limited available field data. The parameterizations may be reduced to Rig-based ones by incorporating the relationship between Rig and turbulence intensity observed in the field. Existing stability functions for two-equation turbulent closure schemes are found to over-predict mixing efficiency at low Fr. Copyright 2012 by the American Geophysical Union.

Anderson S.,Defence Science and Technology Organisation, Australia | Buchan S.,RPS MetOcean Pty Ltd
2014 International Radar Conference, Radar 2014 | Year: 2014

HF radar is an established technology for observing gravity waves on the ocean surface. The dominance of the Bragg scattering mechanism and the acute Doppler sensitivity of such radars enable them to measure both the ocean roughness spectrum and its transformation under advection by surface currents. Several hundred such radars are presently in operation around the world, most delivering maps of surface currents and significant waveheight in near-real time. Some provide estimates of the directional wave spectrum. While the utility of the radar products is unquestioned, it is noteworthy that they are properties of the ocean's surface layer, not of its interior. In many applications it is desirable to know something of the prevailing dynamics of the entire water body, in particular the presence of energetic phenomena which may impact on offshore facilities or otherwise interfere with maritime operations. At present this can be accomplished only by costly in situ point measurements such as thermistor chains and expendable bathythermographs, or inferred under favorable conditions from satellite imagery. Accordingly the question arises, can HF radar, with its vast coverage and persistent surveillance capability, observe and perhaps characterize any of the interior dynamics? In this paper we investigate the possibility of detecting large-scale internal waves via the 'signature' of their interaction with the surface gravity wave field. © 2014 IEEE.

Ward I.,University of Western Australia | Larcombe P.,RPS MetOcean Pty Ltd. | Firth A.,Fjordr Ltd | Manders M.,Dutch Cultural Heritage Agency
Geologie en Mijnbouw/Netherlands Journal of Geosciences | Year: 2014

Since so little is still known of the marine prehistoric environment, present management actions tend to be guided by the gathering of disparate sets of data obtained as part of regulatory practice and/or from opportunistic finds that are not necessarily specifically targeted towards archaeology. Our view is that we need to develop a clearly defined set of questions about the marine prehistoric cultural resource to enable the design of targeted scientific research, as part of both the regulatory process and marine management generally. In this paper we argue that it is crucial to understand both natural and anthropogenic context, and this necessarily includes work on the Quaternary geology. Furthermore, we argue for a greater regulatory emphasis on identifying and initiating what we should do (for the long term) rather than what we can and are doing (for the short term) to identify the best means to manage the prehistoric marine environment. © Netherlands Journal of Geosciences Foundation 2014.

Macdonald R.K.,James Cook University | Ridd P.V.,James Cook University | Whinney J.C.,James Cook University | Larcombe P.,RPS MetOcean Pty. Ltd. | Neil D.T.,University of Queensland
Marine Pollution Bulletin | Year: 2013

Water turbidity and suspended sediment concentration (SSC) are commonly used as part of marine monitoring and water quality plans. Current management plans utilise threshold SSC values derived from mean-annual turbidity concentrations. Little published work documents typical ranges of turbidity for reefs within open coastal waters. Here, time-series turbidity measurements from 61 sites in the Great Barrier Reef (GBR) and Moreton Bay, Australia, are presented as turbidity exceedance curves and derivatives. This contributes to the understanding of turbidity and SSC in the context of environmental management in open-coastal reef environments. Exceedance results indicate strong spatial and temporal variability in water turbidity across inter/intraregional scales. The highest turbidity across 61 sites, at 50% exceedance (T50) is 15.3 NTU and at 90% exceedance (T90) 4.1 NTU. Mean/median turbidity comparisons show strong differences between the two, consistent with a strongly skewed turbidity regime. Results may contribute towards promoting refinement of water quality management protocols. © 2013 Elsevier Ltd.

Shimizu K.,University of Western Australia | Shimizu K.,RPS MetOcean Pty Ltd. | Imberger J.,University of Western Australia
Limnology and Oceanography | Year: 2010

The evolution of damped basin-scale internal waves was investigated using a modal analysis for layer-stratified rotating lakes. A simple model for homogeneous oscillatory boundary layers was incorporated into the modal analysis to predict damping rates of individual internal-wave modes, enabling the prediction of their evolution under wind forcing and bottom friction. Application of the method to Lake Kinneret indicated a different dynamic balance in summer and spring, despite the continuous presence of large amplitude internal waves in the two seasons. In summer, strong diurnal winds continuously excited the dominant Kelvin waves, but the relatively strong damping (e-folding damping times ∼ 3 d) suppressed their amplitudes. In spring, wind forcing was again strong, but intermittent, and it was weaker damping (e-folding damping times ∼ 10 d) that allowed the dominant Poincaré waves to persist until the next wind event. The significant difference in the damping times was due to the difference in the periods and the structure of the internal waves as well as the bottom boundary-layer thickness, which limited the Ekman transport and energy dissipation within the boundary layer. © 2010, by the American Society of Limnology and Oceanography, Inc.

Ward I.,University of Western Australia | Larcombe P.,RPS MetOcean Pty Ltd | Larcombe P.,University of Western Australia | Veth P.,University of Western Australia
Geoarchaeology | Year: 2015

Existing models of coastal occupation, in one form or another, embrace the assumption that changes in mean sea level were the prime driver for shifts in coastal resource productivity of consequence to coastal foragers. Focusing on the North West Shelf of Australia, this paper considers the role of physical sedimentary processes in understanding both past coastal resource productivity and the archaeology of drowned coastal landscapes. From a review of up-to-date literature on sea-level related coastal formation process related to the North West Shelf, we describe the complex interplay of sea-level change and sedimentary processes in determining (i) coastal resource availability, and (ii) archaeological site preservation potential through time. We argue that human behavioral models that have been linked solely to changes in sea level change from ca. 45 ka onward along the Australia continental shelf have inadequately accounted for local sedimentary regimes. It is not past sea-level per se, which is of relevance to coastal productivity and human behavioral ecology models but changes in tidal regimes, coastal configurations and sedimentation. We conclude that our understanding of maritime adaptations for Sahul (Greater Australia) remain incomplete without investigating former coastlines and archaeological information that now lies submerged offshore. © 2014 Wiley Periodicals, Inc.

Shimizu K.,RPS MetOcean Pty Ltd.
Journal of Geophysical Research: Oceans | Year: 2010

An analytical model of capped turbulent oscillatory bottom boundary layers (BBLs) is proposed using eddy viscosity of a quadratic form. The common definition of friction velocity based on maximum bottom shear stress is found unsatisfactory for BBLs under rotating flows, and a possible extension based on turbulent kinetic energy balance is proposed. The model solutions show that the flow may slip at the top of the boundary layer due to capping by the water surface or stratification, reducing the bottom shear stress, and that the Earth's rotation induces current and bottom shear stress components perpendicular to the interior flow with a phase lag (or lead). Comparisons with field and numerical experiments indicate that the model predicts the essential characteristics of the velocity profiles, although the agreement is rather qualitative due to assumptions of quadratic eddy viscosity with time-independent friction velocity and a well-mixed boundary layer. On the other hand, the predicted linear friction coefficients, phase lead, and veering angle at the bottom agreed with available data with an error of 3%-10%, 5°-10°, and 5°-10°, respectively. As an application of the model, the friction coefficients are used to calculate e-folding decay distances of progressive internal waves with a semidiurnal frequency. Copyright 2010 by the American Geophysical Union.

Shimizu K.,RPS MetOcean Pty Ltd.
Journal of Physical Oceanography | Year: 2011

A theory of vertical modes in multilayer stratified fluids is proposed. A matrix notation is introduced to generalize the theory to an arbitrary number of layers. The properties of verticalmodes including their orthogonality are derived. The linearized shallow-water equations and total energy equation are then decomposed into vertical modal components in the presence of large horizontal variations in bottom elevation and stratification, which induce linear interactions among verticalmodes. The theory is applied to the derivation of vertical modes in threelayer stratified fluids and an internal tide generation problem under two-layer stratification. It is shown that the proposed theory correctly approaches the continuous counterpart as the number of layers increases. © 2011 American Meteorological Society.

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