Implementation of the vortex force formalism in the coupled ocean-atmosphere-wave-sediment transport (COAWST) modeling system for inner shelf and surf zone applications

Author Posting. © The Author(s), 2012. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Ocean Modelling 47 (2012): 65-95, doi:10.1016/j.ocemod.2012.01.003.The coupled ocean-atmosphere-wave-sediment transport modeling system (COAWST) enables simulations that integrate oceanic, atmospheric, wave and morphological processes in the coastal ocean. Within the modeling system, the three-dimensional ocean circulation module (ROMS) is coupled with the wave generation and propagation model (SWAN) to allow full integration of the effect of waves on circulation and vice versa. The existing wave-current coupling component utilizes a depth dependent radiation stress approach. In here we present a new approach that uses the vortex force formalism. The formulation adopted and the various parameterizations used in the model as well as their numerical implementation are presented in detail. The performance of the new system is examined through the presentation of four test cases. These include obliquely incident waves on a synthetic planar beach and a natural barred beach (DUCK’ 94); normal incident waves on a nearshore barred morphology with rip channels; and wave-induced mean flows outside the surf zone at the Martha’s Vineyard Coastal Observatory (MVCO). Model results from the planar beach case show good agreement with depth-averaged analytical solutions and with theoretical flow structures. Simulation results for the DUCK’ 94 experiment agree closely with measured profiles of cross-shore and longshore velocity data from Garcez-Faria et al. (1998, 2000). Diagnostic simulations showed that the nonlinear processes of wave roller generation and wave-induced mixing are important for the accurate simulation of surf zone flows. It is further recommended that a more realistic approach for determining the contribution of wave rollers and breaking induced turbulent mixing can be formulated using non-dimensional parameters which are functions of local wave parameters and the beach slope. Dominant terms in the cross-shore momentum balance are found to be the quasi-static pressure gradient and breaking acceleration. In the alongshore direction, bottom stress, breaking acceleration, horizontal advection and horizontal vortex forces dominate the momentum balance. The simulation results for the bar / rip channel morphology case clearly show the ability of the modeling system to reproduce horizontal and vertical circulation patterns similar to those found in laboratory studies and to numerical simulations using the radiation stress representation. The vortex force term is found to be more important at locations where strong flow vorticity interacts with the wave-induced Stokes flow field. Outside the surf zone, the three-dimensional model simulations of wave-induced flows for non- breaking waves closely agree with flow observations from MVCO, with the vertical structure of the simulated flow varying as a function of the vertical viscosity as demonstrated by Lentz et al. (2008).The first two authors were supported by a NOAA/IOOS Grant (Integration of Coastal Observations and Assets in the Carolinas in Support of Regional Coastal Ocean Observation System Development in the Southeast Atlantic) and a cooperative agreement between U.S. Geological Survey and University of South Carolina as part of the Carolinas Coastal Change Processes Project. Also G. Voulgaris was partially supported by the National Science Foundation (Awards: OCE-0451989 and OCE-0535893)

Fractals in Geoscience and Remote Sensing

Abstract not availableNA-NOT AVAILABL

Thermal and chemical imaging of the upper mantle anomalies: application to Western Mediterranean

[eng] The closure of the Ligurian-Tethys Ocean, opened during Jurassic and consisting of highly segmented margins in between Africa and Iberia, has produced the Alboran and Algerian basins in the Western Mediterranean through subduction and slab roll-back processes during the Cenozoic. Towards the end of the slab roll back, collision with the continental margins led to the formation of the Betic-Rif orogen in south Iberia and the Tell-Kabylies in north Algeria. Both, the Betics-Rif and Tell-Kabylies, shows the high-pressure and low-temperature (HP-LT) rocks exhumed from the subduction channel but with opposite tectonic vergence, to the NW in Betics and to the SE in Kabylies. While the Cenozoic evolution of the back-arc basins in the Central and Eastern Mediterranean (i.e., Liguro-Provenca, Tyrrehenian and Aegean) are well understood, the evolution of the Alboran and Algerian basins in the Western Mediterranean is under debate, leading to the proposal of different geodynamic evolution models. All the models agree on that the subduction and subsequent slab-rollback was operating but argues for the direction of subduction trench and slab-rollback. At present, positive seismic velocity anomalies in the upper mantle are observed in the tomography models around the Alboran Basin and beneath the North- Algeria margin. These high velocity anomalies are qualitatively interpreted to be cold, hence, remnant of the subducted Ligurian-Tethys lithosphere in order to explain geodynamic evolution of the Alboran and Algerian basins. Subduction processes must have left its imprint on the crust and upper mantle structure, temperature and chemical composition, which dictate the present-day physical state. Physical state inside the Earth controls the physical properties (i.e., density, seismic velocities, and thermal conductivity) which in turn control the geophysical observables at the surface (i.e., elevation, gravity anomaly, geoid height, and surface heat flow). Integrated geophysical-petrological modelling of these surface observables allows exploring and reconciling observations from different datasets and methods. However, thermal and/or chemical nature of the imaged seismic velocity anomalies (e.g., subducted Ligurian-Tethys) needs to be incorporated in such models. In general, seismic tomography models reports relative positive or negative velocities with respect to a reference model which are further inferred qualitatively as cold or hot regions in the upper mantle, respectively. Quantitative interpretation of the seismic velocity anomalies in terms of temperature and/or chemical composition is challenging and is at the forefronts of the modern day geophysics. Hence, the objectives of this thesis is twofold: 1) to develop a methodological framework to incorporate the sublithospheric anomalies observed in seismic tomography in the integrated geophysical-petrological modelling of the geophysical surface observables, and 2) its application to the Alboran and Algerian basins and their margins to model the present-day crust and upper mantle thermo-chemical structure yielding temperature, density (i.e., chemical composition) and seismic velocities to put constrains on their geodynamic evolution. In the first part, an already existing tool, LitMod2D_1.0, is improved into a new LitMod2D_2.0 version which allows to model the sublithospheric anomalies and to be available for the scientific community. Various synthetic tests of the upper mantle anomalies have been performed to understand the sensitivity of temperature and chemical composition to the density and seismic velocities. Results show nonlinearity between the sign of thermal and seismic velocity anomalies, and that S-wave velocities are more sensitive to temperature whereas P-wave velocities are to composition. A synthetic example of subduction is made to understand the sensitivity of sublithospheric mantle anomalies associated with the slab and the corner flow, on surface observables (elevation, geoid height, and gravity anomalies). A new open‐source graphic user interface is incorporated in the new version for ease of application. The output of the code is simplified by writing only the relevant physical parameters (temperature, pressure, material type, density, and seismic velocities) to allow the user to utilize predefined post‐processing codes from a toolbox (flexure, mineral assemblages, synthetic passive seismological data, and tomography) or designing new ones. A post-processing example is demonstrated by calculating synthetic seismic tomography, Rayleigh-surface‐wave dispersion curves, P-wave receiver functions and stable minerals distribution from the output file of LitMod2D_2.0. In the second part of this thesis, I apply improved LitMod2D_2.0 to define the present day crustal and lithospheric structure along two 2D geo-transects beneath the Betics-Alboran and Greater Kabylies-Tell-Algerian orogenic systems to discuss the highly debated and contrasting existing models. Results show a thick crust (37 km and 30 km) and a relative deep LAB (130 km and 150 km) underneath the HP-LT metamorphic units of the Internal Betics and Greater Kabylies that contrast with the ~16 km thick magmatic crust of the Alboran Basin and the ~10 km thick oceanic crust of the Algerian Basin, respectively. This sharp change in crustal thickness, from the orogenic wedge to the back-arc basins, contrasts with the gentler crustal thickening towards the respective opposed margins. Despite the similar LAB depth (~60 km) in both basins, the chemical composition of the lithospheric mantle beneath the Alboran Basin is slightly more fertile than beneath the Algerian Basin. At sublithospheric levels, results show that both the Alboran slab beneath the Betics and Algerian slab beneath the Kabylies, are about -400 oC colder than the ambient mantle but have different chemical composition. Alboran slab is slightly fertile compared to the typical oceanic lithospheric of the Algerian slab. Both slabs are detached from the respective continental lithospheric mantle of Iberia and Africa, since their weight is not transmitted isostatically to the surface. Results show that the uplift related to the slab break-off is ~700–1000 m in the Betics and is ~600–1200 m in north Algeria. The Ligurian-Tethys slab beneath the SE Iberia shows an apparent dip to the SSE whereas the slab below Algeria dips to the NNW, matching the NW- and SE-tectonic transport direction of the fold and thrust belts of the Betics and Greater Kabylies-Tell-Atlas subduction-related orogens, respectively. The large-scale configuration of present-day SE Iberia and Algerian margins as well as their mantle compositions in the Alboran and Algerian geo-transects is consistent with opposite dipping subduction of two segments of the Jurassic Ligurian-Tethys domain. Their present configurations agree with Neogene slab roll-back process triggering mantle delamination followed by slab break-off in both opposite subductions

A 3D unstructured grid nearshore hydrodynamic model based on the vortex force formalism

Acknowledgments This work was partly supported by joint Engineering and Physical Science Research Council (EPSRC) UK and Technology Foundation STW Netherlands funded SINBAD (EP/J005541/1) project. P. Zheng was supported by the China Scholarship Council during his four-year PhD study at the University of Liverpool. We would like to thank Prof. C.S. Chen of the University of Massachusetts-Dartmouth for providing the source code of FVCOM and also the SWAN developers for developing and providing this open source code. We would also like to thank the staff and personnel involved in collecting and maintaining the DUCK’94 experiment dataset and the anonymous reviewers for their constructive comments and suggestions. Computational support was provided by the Chadwick High Performance Computer at University of Liverpool and also the facilities of N8 HPC Centre of Excellence, provided and funded by the N8 consortium and EPSRC (EP/K000225/1).Peer reviewedPublisher PD

Ocean colour remote sensing of the Great Barrier Reef waters

The research undertaken has developed relationships between the concentrations of optically-significant substances (phytoplankton, Colour Dissolved Organic Matter (CDOM), and particulates) found in Great Barrier Reef waters and their respective inherent optical properties. Based on this knowledge, a physics-based spectral deconvolution routine was developed that successfully retrieved the concentrations of these substances from passive ocean colour observations such as those from the MODIS imaging satellite

On the formation, ventilation, and erosion of mode waters in the North Atlantic and Southern Oceans

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94834/1/jgrc12564.pd

Developing an Unstructured Grid, Coupled Storm Surge, Wind Wave and Inundation Model for Super-regional Applications

During extreme weather conditions such as hurricanes and nor\u27easters, both the currents and wind waves generated by the atmospheric forces are important. Although they may act and dominate on different temporal and spatial scales, their interactions and combined effects are without doubt significant. In this dissertation, a major effort has been made to couple an unstructured grid circulation model SELFE (semi-implicit, Eulerian-Lagrangian finite element model) and the WWM II (Wind Wave model II). Moreover, this new coupled model system can be executed in a parallel computational environment. After the coupled model was successfully built, the model was verified with ideal test cases, either through comparisons with analytic solutions or with laboratory experiments. It was further validated by field-measured data during two hurricane events. The SELFE-WWM II model framework described above was used to participate in a SURA testbed project that was recently funded by the NOAA IOOS program. The purpose was to improve the storm surge and inundation modeling skill throughout the Gulf of Mexico as well as along the U.S. East Coast. The coupled tide, surge, and wind wave models in two and three dimensions were tested and compared systematically. Two well-known cases were investigated in detail. One was the event of Hurricane Ike of 2008 in the Gulf of Mexico and the other was the April Nor\u27easter of 2007 in the Gulf of Maine. For the Gulf of Mexico study, the key scientific issue is the origin of the forerunner. It has long been recognized that the forerunner plays an important role in generating large hurricane-induced storm surge in the Gulf of Mexico. The forerunner is a phenomenon whereby water level throughout the vast coastal region was elevated days before the hurricane makes landfall. The forerunner can contribute significantly to the total water level that results subsequently during the primary surge when the hurricane makes landfall. The 2008 Hurricane Ike, which devastated the Galveston Bay along the Texas Coast, is a good example: 1.4 m out of 4.5 m maximum surge was contributed by the forerunner in the Gulf of Mexico. The consensus from initial results of multiple models indicates that the forerunner occurred as a result of Ekman set-up along the broad Louisiana-Texas (LATEX) shelf by the shore-parallel wind field. By contrast, the primary surge was dominated by the low pressure and the maximum wind along a path perpendicular to the shore as the hurricane made landfall. It was found that the cross-shore Ekman set-up is highly sensitive to the bottom boundary layer (BBL) dynamics, especially to the drag coefficient. Given the fact that the Gulf of Mexico is known to be rich in fluid mud, and near-bed flows generally are very weak under fair-weather conditions, one plausible hypothesis is that, during the stormy condition, the suspended sediment-induced density stratification is likely to be ubiquitously present at the bottom boundary layer. A sediment-transport model and wave-current bottom boundary layer sub-model including the sediment-induced stratification effect were coupled to the unstructured grid circulation and wind wave model (SELFE-WWM II) for simulating the forerunner during Hurricane Ike. The model results demonstrate that the bottom boundary layer dynamics have a significant effect on the velocity veering as well as the Ekman set-up across the shelf. In the Gulf of Maine study, the high-resolution coupled SELFE-WWM II model was applied in the Scituate Harbor, a small, shallow coastal embayment, south of Boston. The key issue for the study was the recurring inundation related to the role played by wind waves during nor\u27easter events. With limited observation data in the Scituate, the model result from SELFE was compared with that from FVCOM. The major findings are summarized as follows: (1) wind waves generated by the nor\u27easter can profoundly affect the coastal current by increasing the magnitude and altering its direction, (2) while the mean water level inside the Harbor stays the same, the total transport across the harbor mouth increases when wind waves are included, and (3) the total inundation area, primarily in the northern and southern basins within the Harbor, does increase when wind waves are included. There is a question as to why the inclusion of the wind waves did not cause the mean water level to change inside the Harbor while the inundation area was increased. The plausible explanation is that this lack of impact could be that the Stokes transport was small and the increase of water level by the wave set-up was compensated by the expansion of the inundation area in the shallow region