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School of Physical, Environmental and Mathematical Sciences |
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Physical Oceanographer
Research Interests:
Physical oceanography in bays and estuaries. Numerical modelling in shallow seas. Bottom boundary layer and sediment transport dynamics. Coastal Integrated Management Systems.
Biography
Xiao Hua Wang graduated from Ocean University of Qingdao, China and completed his PhD in physical oceanography in 1990 at James Cook University in Australia. He held a research position at the School of Geography and Oceanography (currently School of Physical, Environmental and Mathematical Sciences), the University of New South Wales at Australian Defence Force Academy, Canberra, Australia before he became a faculty member in the same school since 1991. He was tenured in 1996. He has been a visiting scientist at Princeton University, USA, and a visiting professor at University of Bologna, to undertake collaborative research projects. On 1 July 2006 he was promoted to Senior Lecturer. He is also an Adjunct Professor at the Ocean University of China.
Research
Current Research
Oceanic nepheloid layers and their role in coastal oceanography
Nepheloid layers in the oceans, formed through sediment resuspension events by waves and currents on the continental shelf, ‘shut down’ the bottom boundary layer processes and reduce mixing and hence transport of sediments and other materials. This project will develop and implement new numerical models to investigate the dynamic features of such layers including their highly nonlinear behaviours of resuspension hysteresis. The impact of such layers in determining coastal ocean and ecosystem dynamics and in transporting sediments from the rivers into the outer shelves of the marginal seas will be investigated. This project covers the coastal oceans such as Jervis Bay, NSW, the Adriatic Sea, Italy, the southwestern coast of Korea and East China and Yellow Seas. The outcome of the project will result in new knowledge on the roles that resuspended sediments played in flow dynamics and the primary biomass production in the turbid coastal ecosystem environments.
IMOS(Integrated Marine Observing System) NSW node – Jervis Bay mooring
UNSW@ADFA researchers have investigated the oceanography of Jervis Bay and its adjacent shelf since 1988 spurred by the interest of Defence. In this proposal, we aim to construct and deploy a pair of moorings at a site off Jervis Bay to extend this data set. The primary purposes of the moorings are to provide real-time observational capability and obtain longer records to be used for on-going oceanographic and climate studies at UNSW@ADFA. All observations will be incorporated into IMOS (Integrated Marine Observing System) and BlueNet. Our mooring complements NSW-IMOS' planned observational infrastructure.
Coastal environment management Comparative study of marine protected areas in Australian and China
The project aims to compare the legislative frameworks, management characteristics and impact of the ecosystems of the marine protected areas in Australia and in China. It is widely known that China has a growing interest in developing marine protected areas and management plans in its coastal zones whilst Australia has a well developed integrated coastal management system. This study will be a comparative analysis of the advantages and disadvantages of coastal environmental management systems in two countries. It is hoped that the present work can assist and enhance management of the marine protected areas both in Australia and in China.
Managing Australian Defence Force activities in marine protected areas - The environmental management of Jervis Bay and Shoalwater Bay Training Areas
This project aims to study coastal management issues of Australia Defence Force (ADF) activities in Australian Marine Protected Areas, by analysing the Environmental Management Systems of Jervis Bay and Shoalwater Bay training areas. The research has important significance to the sustainable development of ADF training activities, ecology, environment, economy and society. At the completion of this project, we hope to provide experiences and lessons learnt from managing these two training areas in an environmentally sustainable manner; and to assist management of ADF training activities in other regions.
Research Collaborators
- Prof. X. Bao (Ocean University of China, Qingdao)
- Dr D-S. Byun (National Oceanographic Research Institute, Korea)
- Dr L. Oey (Princeton University, USA)
- Prof. N. Pinardi (Bologna University, Italy)
- Prof. D. Wu (Ocean University of China, Qingdao)
PhD Opportunities and Scholarships
If you are interested in a PhD or Masters by Research in Physical Oceanography:
Contact: Dr Xiao Hua Wang, h.wang@adfa.edu.au
Further information concerning scholarships at: http://www.unsw.adfa.edu.au/pems/student/pgrescourses.html
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Oceanography students with Dr Xiao Hua Wang outside PEMS South building. From L to R: Qun Liang, Vihang Bhatt, Dr Xiao Hua Wang, Donghui Jiang. [Photo credit: K. Badek] |
Recent Research
Bottom boundary layer dynamicsModelling of sediment transport dynamics in the coastal oceans
Water circulation coastal embayment
Tidal dynamics
Bottom boundary layer dynamics
1. Bottom boundary layer and pressure compensation
It is an observed characteristic of oceans that velocities and horizontal pressure gradients are larger near the ocean surface than they are in deeper water. This is conventionally labeled "pressure compensation" whereby baroclinic structure, comprising sloping isopycnal surfaces, is adjusted so that surface pressure gradients are reduced in deeper water. In collaboration with Prof George Mellor of Princeton University, USA, we numerically modelled a two-dimensional flow in a channel to demonstrate the baroclinic adjustment process and its relationship to the bottom boundary layer (BBL). A simple analytical model is also developed and defines the timescale of the adjustment process. Refer to Mellor and Wang (1996) for details.
Figure: Shown below are five year evolution of the BBL and the pressure compensation during a spin-up of an alongshore, elevation-gradient-driven flow at thecentre of an deep ocean channel. (a) Alongshore velocities. (b) Cross-shore velocities.(c) Density relative to the initial bottom density. (d) Mixing coefficient determined by Mellor-Yamada 2.5 turbulence closure scheme.
[Click on image for larger view].
2. Fluid-mud layer and its effect on the BBL dynamics
In the high-energy environment of coastal seas and estuaries, fluid-mud layers often develop near the seabed. They are maintained by frequent and strong sediment resuspension events driven by surface waves and tides. The waters in the bottom boundary layers (BBL) can be stratified due to the presence of this layer through the coupling effect of the high concentration of resuspended sediment and the water density. Hydrodynamic characteristics of the stratified BBLs are significantly different than those in well-mixed BBLs. In some resuspension events in turbid tidal estuaries and coastal seas, sediment is abnormally concentrated within a thin wall layer that is overlain by a thicker layer with much smaller concentration.
These resuspension events are termed "resuspension hysteresis" with respect to the tidal forcing frequency. The processes that control these resuspension hysteresis events have not been understood in past. We used a numerical sediment transport model in an idealized estuary with a muddy bed to study the dynamics of the sediment-stratified BBL in general, and resuspension hysteresis in particular. The seawater density and the sediment concentration were coupled in the sediment transport model. As a result the model develops a lutocline (a thin layer, between the fluid-mud layer and overlying water, in which the vertical sediment concentration gradient is at a maximum). The settlement of the lutocline leads to a resuspension hysteresis. Both the sediment settling velocity and the turbulence intensity control the frequency of these events, which is lower than that of the tidal forcing.
Our study is summarized in a poster by Wang (2002) Tide-induced Sediment Resuspension and the Bottom Boundary Layer in an Idealized Estuary with a Muddy Bed (Adobe Acrobat).
Figure: Model-simulated time series of sediment concentration (C) and flux (Q) near the entrance of an idealistic estuary, where the tides are the only forcing function for sediment resuspension. Sediment resuspension hysteresis can be observed in the figure (top panel) and is caused by the fluid-mud layer effect in the BBL of the estuary.
[Click on image for larger view].Modelling of sediment transport dynamics in the coastal oceans
1. Jervis Bay, NSW, Australia
A numerical study of sediment transport in a coastal embayment during winter storms
A coupled Jervis Bay hydrodynamic model and sediment transport model was established to study the dynamics of suspended sediment transport in small coastal embayment during winter storms that caused strong winds and surface heat loss. The coupled model resolved the bottom boundary layer with high vertical resolution, and considered the mechanism of the wave-current interaction. The study confirmed an observational characteristic that surface water in the northern bay could be visually ‘murky’, and concluded that the water murkiness was caused by wave erosion of fine sediments in the northern shallow region. The study also reviewed that the flushing of sediments of both classes were inefficient in the bay. After the winter storms, all coarse sediments had remained in the bay while a small fraction (<25%) of fine sediments had been flushed out of the bay into the adjacent shelf. This suggested that once they were discharged, particulate matters largely remained in the bay for a long time if not permanently.
Figure: Shown above are model simulated surface and bottom suspended sediment concentration one day after the winter storms. FSM and CSM are concentration for the fine and coarse sediment materials respectively. |
2. The Adriatic Sea, Italy
Modelling the dynamics of sediment transport and resuspension in the Northern Adriatic Sea
A coupled Adriatic Sea General Circulation and sediment transport model was used to study the dynamics of coarse and fine sediment transport and resuspension in the Northern Adriatic Sea. The sediment sizes of coarse 
and fine
materials were sorted by their settling velocities. The bottom boundary layer (BBL) was discretized by a vertical sigma coordinate system with high resolution, and the wave-current interaction mechanism was considered. The sediment distributions and fluxes under various forcing conditions such as the Po River plume, the Bora and Scirocco wind stress and the surface waves were studied by process oriented numerical simulations. The conclusions are that maximum northward sediment transport occurs under the forcing by the Po River plume with the Scirocco wave resuspension. The largest southward sediment transport was due to the combined effect of the Po River plume and the Bora wind forcing under the Bora wave conditions. A realistic forcing numerical experiment was also conducted for November 1994 when the full range of forcing functions were experienced by the region. This study shows that wave driven sediment resuspension is a dominant resuspension mechanism in the shallow coastal areas of Northern Adriatic Sea, and contributes significantly to the complexity of the sediment distribution and flux features in the region.
A
[Click on image for larger view].
B
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Figure: (a) Adriatic Sea General Circulation Model domain and the Adriatic Sea bathymetry with directions of Bora and Sirocco winds denoted. (b) Submodel domain of the Northern Adriatic Sea.
3. The Mokpo Coastal Zone, Korea
Sediment transport dynamics in the extended Mokpo Coastal Zone Korea
The EMCZ region is characterized by a tidally-dominated, ebb dominant regime with scattered islands. In collaboration with Mr Do-Seong Byun, a sediment transport model coupled to a 3-D ocean model is used to explore the effects on the sediment dynamics of first ebb-dominant tidal asymmetry by means of the M4 tide and second sediment-induced stratification in the bottom boundary layer (BBL). This study contributes to the understanding of the mechanisms of formation of intertidal mudflats well-developed along the coast and around island, and of the long sand ridges.
[Click on image for larger view].
Figure:Sediment erosion and deposition after 29 days of model simulation. (a) Model run without the effect of sediment stratified BBL, (b) model run with the effect of sediment stratified BBL.
Water circulation coastal embayment
1. Low frequency flow in Jervis Bay, NSW
On Sub-inertial Flow in A Small And Stratified Embayment
Princeton Ocean Model is used to study the response of Jervis Bay, NSW, Australia to the local wind and remote shelf coastal trapped wave (CTW) forcings in summer seasons when the water column is stratified by the water temperature. The study has revealed that the response of bay to the wind forcing is the generation of the wind driven currents and the internal Kelvin waves (IKW). However, both temperature and flow sub-inertial oscillations in the bay are weaker than those from the observations and the correlation between the modeled and observed low frequency currents is low. In response to the forcing of CTWs on the adjacent shelf, IKWs are also established in the bay and amplitudes of sub-inertial oscillations of temperature and currents are better compared with the observations. It can be concluded that sub-inertial baroclinic flows in the bay is dominantly forced by remote CTW on the shelf, adjacent to Jervis Bay during thermally stratified summer seasons. This work is described by Wang and Wang (2003).
Figure: The numerical simulated amplitude of the temperature oscillation with 8 day period from the wind forced model and the CTW forced model CI abbreviates contour interval
[Click on image for larger view].
2. Jervis Bay circulation due to sea surface cooling
Coastal Embayment Circulation due to Atmospheric Cooling
Wang and Symonds (1999) has combined observations of temperature and salinity distributions and currents with numerical simulations to investigate the response of a coastal embayment to atmospheric cooling during winter. The field experiment, including current meter mooring, CTD surveys and weather monitoring was carried out in Jervis Bay, NSW, Australia, for the period July to October, 1996. The bay is small enough that a synoptic CTD survey can be achieved over a period of six hours but still large enough that Coriolis effects are important. During a cooling event vertical convection and surface wind stress combined to produce a well mixed water column. Continued cooling produced cold, dense water in the shallow regions of the bay and could be identified as a tongue of cold bottom water flowing out of the bay onto the adjacent shelf. The cold outflow produced a surface inflow to the bay of warmer shelf water causing the bay waters to restratify. The response has been modelled using the three dimensional Princeton Ocean Model with a prescribed surface heat flux based on meteorological observations. Following a period of cooling the model produced a stronger anti-cyclonic gyre at the surface and a weaker cyclonic gyre nearer the bottom. As the cold bottom water flowed out of the bay, warm shelf water entered at the surface and the anti-cyclonic gyre was replaced by two counter rotating gyres; cyclonic in the north and anti-cyclonic in the southern half of the bay. In order to achieve a quantitative agreement between the model and observations including the restratification following the cooling event and flow reversal associated with the change from anti-cyclonic to cyclonic circulation in the northern half of the bay, the surface heat fluxes needed to be artificially increased to compsensate for excessive mixing in the model. The model results predicted a flushing time of order one week depending on the duration and magnitude of the surface cooling and the initial conditions in the bay.
Animation shows the model simulated Bay circulation forced by the cooling event.
Figure: Shown below are surface and bottom temperature distributions in Jervis Bay from the CTD surveys conducted immediately before (July 9, 1996) and after (July 17, 1996) the cooling event.
[Click on image for larger view].
Tidal dynamics
1. The Hey River Estuary, northern Queensland, Australia
In collaboration with Dr Peter Craig of CSIRO, Marine Laboratory, a simple model of open coastal dynamics is developed to provide an analytic solution of the vertical and axial structure of tidal currents in an estuary. Applied to the Hey River estuary in the Gulf of Carpentaria, Australia, the model provides an accurate representation of the four major tidal constituents. Bottom boundary considerations indicate that the data are consistent with the concept of a bottom logarithmic layer 0.6 m deep, in which the eddy viscosity increases linearly from near-zero to its free-stream value.
2. The Mokpo Coastal Zone, Korea
In collaboration with Mr Do-Seong Byun, the results of tidal analyses of long term (1971-2001) sea-level elevation records at Mokpo observation station on the western tip of the south-west coast of Korea showed a significant changes in tidal amplitudes, together with advance in phases for the major constituents as a result of constructing a dyke and two sea-walls in the MCZ. According to the stages of construction, the amplitudes of each tidal constituent, rather than the phases showed different variability patterns. The semidiurnal (M2 and S2), and fourth-diurnal (M4 and MS4) amplitudes increased significantly in the post-dyke construction, whereas the diurnal (K1 and O1) amplitudes decreased slightly in the post-seawall construction. That is, the semidiurnal and fourth-diurnal amplitudes were markedly affected by the dyke construction, and less affected by the two sea-walls construction. In contrast, the diurnal amplitudes were little influenced by the dyke construction, and slightly influenced by the two sea-walls construction.
Three numerical simulations with different stages of construction reveal that an increase/advance in tidal amplitudes/phases in Mokpo Harbour is closely related to change in the MCZ system from a choked coastal system to a non-choked system. Before the construction, amplitudes/phases inside channels such as Mokpogu were lower/more delayed than those outside due to narrow channels in comparison with large capacity of water storage inside the MCZ. Reduction in capacity of water storage induced by the series of constructions in the MCZ shifts the complex hydraulic system to a simple non-choked system. Therefore, the difference in tidal amplitudes and phases between inside and outside the channels is significantly reduced by the construction.
Figure: Model simulated M2 tides.
[Click on image for larger view].
3. The Jindo Island, Korea
In collaboration with Mr Choel Cho and Dr Yang-Ki Cho from Chonnam National University, Korea, a 3d tidal model is developed for the Jindo area, south-west coast of Korea. We found that the tides of the area are entirely characterized by a strong tidal current due to the large tidal range and the funnel-shaped Myongrang Strait (Fig.1). As a result of bottom topography and shallow coast, the main tidal stream flows through the centre of the study area and tidal currents are weak around the Modo Island. The directions of tidal ellipses are parallel to the Hoidong coast. It may suggest that the suspended sediments such as mud may deposit to the Hoidong coast between the Hoidong coast and the Modo Island. The complicate feature about tide-induced residual currents is based on the gradient of velocity shear (Ahn et al., 1993). The trend of tide-induced residual currents around Modo shows small vortices. There is a clockwise vortice on the eastern area between the Hoidong coast and the Modo Island, and an anticlockwise vortice on the western area between them. It shows that the suspended sediments such as mud may deposit to the Hoidong coast although tide-induced residual currents are weak.
Figure 1: Model prediction of surface M2 tidal ellipse.
[Click on image for larger view].
Teaching
Oceanography courses with a major and/or sub-major (minor) are offered to the Officer Cadets of the Australian Defence Force Academy. The degrees are awarded by the University of New South Wales. Higher degrees in PhD and MSc (by research) are available to national and overseas candidates.
Recent Publications
Simmonds, F., Wang, X. H. & Lees, B., Comment on ‘Marine GIS: Identification of mesoscale oceanic thermal fronts’, International Journal of Geographic Information Science, in press.
Zhao, L. D., Zhang, Y., Wang, X. H. & Lees,
B. G., 2008, A lesson from Australian
marine parks for promoting the income
of our fisher folk, Fishery Economics
Research, in press.
Byun, D., Wang, X. H., Zavatarelli, M. & Cho, Y., 2007, Effects of resuspended sediments and vertical mixing on phytoplankton spring bloom dynamics in a tidal estuarine embayment, Journal of Marine Systems, 67(1-2),102-118.
Wang, X. H., Pinardi, N. & Malacic, V., 2007, Sediment transport and resuspension due to combined motion of wave and current in the northern Adriatic Sea during a Bora event in January 2001: A numerical modelling study, Continental Shelf Research, 27(5), 613-633.
Zhao, L. & Wang, X. H., 2007, Economics
Study on Marine Disaster and Marine
Income, Economic Science Press,
Beijing, China.
Zhao, L. & Wang, X. H., 2007, The enlightenment on our marine disaster and income from Australian Marine Parks Zone Plan, in Economics Study on Marine Disaster and Marine Income, L. Zhao, X. H. Wang (eds), Economic Science Press, Beijing, China.
Bhatt, V., Wang, X. H. & Morrison, J., 2007, Simulation of the east Australian current and its annual variability and separation using a regional ocean model, AMSA 2007 - Marine Science in a Changing World, University of Melbourne, 9-13 July 2007, Melbourne, p. 25.
Wang, X. H., 2006, Interactive comment on ‘Nesting operational forecasting models in the Eastern Mediterranean: active and slave mode’ by S.S. Sofianos et al., Ocean Science Discussions, 3(4), 1225.
Wang, X. H., Oddo, P. & Pinardi, N., 2006, On the bottom density plume on coastal zone off Gargano (Italy) in the southern Adriatic Sea and its interannual variability, J. Geophys. Res., 112 (C3), C03S17, doi:10.1029/2005JC003110.
Byun, D.S. and Wang, X.H., 2005, Numerical studies on the dynamics of tide and sediment transport in the western tip of the southwest coast, Korea. Journal of Geophysical Research, 110 (C03011), 10.1029/2004JC002459.
Wang, X.H., 2005, Circulation of the northern Adriatic Sea (Italy) due to a Bora event in January 2001: a numerical model study, Ocean modelling, 10, 253-271.
Byun, D.S., X.H. Wang and P.E. Holloway, 2004, Tidal characteristic adjustment due to dyke and seawall construction in the Mokpo Coastal Zone, Korea, Estuarine, Coastal and Shelf Science, 59, 185-196.
Wang, X.H. and Paull, D., 2003, Can Landsat imagery provide hi-resolution mapping of sea surface temperature in a small embayment after a convective cooling. In: Proceedings of SPIE's Vol. 4892: Ocean Remote Sensing and Applications, Robert J. Frouin, Yeli Yuan, Hiroshi Kawamura (eds), (SPIE, Bellingham, WA, 2003), 426-433.
Wang, X.H. and Pinardi, N., 2002, Modeling the dynamics of sediment transport in the Northern Adriatic Sea, Journal of Geophysical Research, 107 (C12), 10.1029/2001JC001303.
Wang, X.H., 2002, Tide-induced sediment resuspension and the bottom boundary layer in an idealized estuary, Journal of Physical Oceanography, 32, 3113-3131.
Recent Grants
External Grants
- X.H. Wang, Nepheloid layers and their role in the coastal oceanography in muddy Chinese estuaries, Second Institute of Oceanography, State Oceanic Administration, China, $4,600, 2008-2009.
- X.H. Wang, Oceanic nepheloid layers and their role in coastal oceanography, APAC Merit Allocation Scheme competitive grant, 1200 su, 2008.
- X.H. Wang, Scientific visit to Korea, Australian Academy of Science, $3,000, 2008.
- D. X. Wu & X.H. Wang et al (40 partners), Evolution of the physical oceanography in the continental shelf margin of the East China Sea and its marine environmental effect, The Chinese Ministry of Science and Technology, AU$ 4.8 million, 2006-2010.
- X.H. Wang & L. A. Wong: Nepheloid layers and their role in the coastal oceanography in the Changjiang (Yangsze) River estuary, Endeavour Australia Cheung Kong Awards, $26,000, 2006.
- N. Pinardi & X.H. Wang et al (42 partners): Mediterranean ocean Forecasting System: Toward environment predictions, EU V Framework, Euro11.97 million (AU$21 million, Euro0.57=AU$1, 2003-2005).
UNSW Grants
- X.H. Wang, An operational sea state and circulation forecast system for Jervis Bay, NSW - A pilot study, UNSW@ADFA Defence-Related Research PhD scholarship scheme + DSTO Top–up (2008-2010).
- X.H. Wang & B. Lees, Managing Australian Defence Force activities in marine protected areas - using Jervis Bay as a case study, Special Research Grant, 2007: $3,000.
- X.H. Wang, The effect of the fluid-mud layer on ocean dynamics in coastal seas, UNSW@ ADFA RTS PhD Scholarship (2006-2008).
Community Service
- Member (2003-2007), ACT Government Council for Education Export.
- Honorary Ambassador for Canberra--Australia's National Capital (2004-).