High resolution tidal model of Canadian Arctic Archipelago, Baffin and Hudson Bay

Ice induced variability of tides in the Canadian Arctic Archipelago, including Baffin Bay and Hudson Strait/Hudson Bay system, was studied by means of a new high resolution tidal model. Here we show that the seasonal variations of the tidal constants are significant in the major part of the domain. Month to month changes of the tidal phases can reach 180 degrees due to changes in the number and positions of the amphidromic points, whereas the amplitude variations are especially large in the near resonant basins. We also show that the tidal seasonality has undergone dramatic changes in the past decades due the decaying extent of the Arctic sea ice. These seasonal/decadal scale changes not only vary tidal dissipation on the shelf, but also impact tides in the adjacent open ocean and, therefore, cannot be neglected.Environmental Fluid Mechanic

Kralendijk Declaration, recommendations from Coastal Dynamics and Ecosystem Change: Caribbean, Quo Vadis?: Bonaire, October 18-21, 2016

The Kralendijk Declaration is the outcome of the conference on "Coastal Dynamics and Ecosystem Change: Caribbean, Quo Vadis?" that was held on Bonaire, October 18-21 2016.Environmental Fluid Mechanic

Shingle 2.0: Generalising self-consistent and automated domain discretisation for multi-scale geophysical models

The approaches taken to describe and develop spatial discretisations of the domains required for geophysical simulation models are commonly ad hoc, model- or application-specific, and under-documented. This is particularly acute for simulation models that are flexible in their use of multi-scale, anisotropic, fully unstructured meshes where a relatively large number of heterogeneous parameters are required to constrain their full description. As a consequence, it can be difficult to reproduce simulations, to ensure a provenance in model data handling and initialisation, and a challenge to conduct model intercomparisons rigorously. This paper takes a novel approach to spatial discretisation, considering it much like a numerical simulation model problem of its own. It introduces a generalised, extensible, self-documenting approach to carefully describe, and necessarily fully, the constraints over the heterogeneous parameter space that determine how a domain is spatially discretised. This additionally provides a method to accurately record these constraints, using high-level natural language based abstractions that enable full accounts of provenance, sharing, and distribution. Together with this description, a generalised consistent approach to unstructured mesh generation for geophysical models is developed that is automated, robust and repeatable, quick-to-draft, rigorously verified, and consistent with the source data throughout. This interprets the description above to execute a self-consistent spatial discretisation process, which is automatically validated to expected discrete characteristics and metrics. Library code, verification tests, and examples available in the repository at https://github.com/shingleproject/Shingle</a. Further details of the project presented at http://shingleproject.org.Environmental Fluid Mechanic

An accurate momentum advection scheme for a z-level coordinate models

In this paper, we focus on a conservative momentum advection discretisation in the presence of zlayers. While in the 2Dcase conservation ofmomentum is achieved automatically for an Eulerian advection scheme, special attention is required in the multi-layer case. We show here that an artificial vertical structure of the flow can be introduced solely by the presence of the z-layers, which we refer to as the staircase problem. To avoid this staircase problem, the z-layers have to be remapped in a specific way. The remapping procedure also deals with the case of an uneven number of layers adjacent to a column side, thus allowing one to simulate flooding and drying phenomena in a 3D model.Hydraulic EngineeringCivil Engineering and Geoscience

Wind and waves in extreme hurricanes

Waves breaking at the ocean surface are important to the dynamical, chemical and biological processes at the air-sea interface. The traditional view is that the white capping and aero-dynamical surface roughness increase with wind speed up to a limiting value. This view is fundamental to hurricane forecasting and climate research but it has never been verified at extreme winds. Here we show with observations that at high wind speeds white caps remain constant and at still higher wind speeds are joined, and increasingly dominated, by streaks of foam and spray. At surface wind speeds of ?40 m/s the streaks merge into a white out, the roughness begins to decrease and a high-velocity surface jet begins to develop. The roughness reduces to virtually zero by ?80 m/s wind speed, rendering the surface aero-dynamically extremely smooth in the most intense part of extreme (or major) hurricanes (wind speed > 50 m/s). A preliminary assessment shows that cross swell, dominant in large regions of hurricanes, allows the roughness under high wind conditions to increase considerably before it reduces to the same low values.Hydraulic EngineeringCivil Engineering and Geoscience

A multiscale analysis of the stability of Caribbean coastal ecosystems through the biogeomorphic modelling of its complex bays and inlets

The Dutch Caribbean consists of two island groups, the Leeward Antilles off the Venezuelan coast separated from the Windward Islands east of Puerto Rico over distances of the scale of the Caribbean Sea itself. Climate change in the Caribbean Sea is predicted to lead to rising sea levels, warming waters and changing eddy fields. Warming waters lead to an increase in the intensity and occurrence of tropical storms and hurricanes, and are linked to an increased risk of surge flooding. Changing eddy fields are likely to affect the path of storm tracks. All of which further influence the environment of the Caribbean, and hence the stability of its ecosystems.Environmental Fluid Mechanic

Accurate vertical profiles of turbulent flow in z-layer models

Three-dimensional hydrodynamic z-layer models, which are used for simulating the flow in rivers, estuaries, and oceans, suffer from an inaccurate and often discontinuous bottom shear stress representation, due to the staircase bottom. We analyze the governing equations and clearly show the cause of the inaccuracies. Based on the analysis, we present a new method that significantly reduces the errors and the grid dependency of the results. The method consists of a near-bed layer-remapping and a modified near-bed discretization of the k???? turbulence model. We demonstrate the applicability of the approach for uniform channel flow, using a schematized two-dimensional vertical model and for the flow over a bottom sill using the Delft3D modeling system.Hydraulic EngineeringCivil Engineering and Geoscience

Sediments and Subgrid: A Great Combination

Long term morphodynamic simulations are used for predicting the impact of climate change and human interventions in our estuarine and coastal regions. The accuracy of this type of simulations suffers generally from low resolution grids. Eventhough high resolution bathymetry data is increasingly more available thanks to new measurement techniques. However, the computational effort for such high resolution simulations is high. Even with increasing computer power and by using the various available techniques for speeding up simulations [Roelvink (2006) ], the computational effort remains high. By introducing a subgrid based method for morphodynamics, we aim at increasing theaccuracy of coarse grid based morphodynamic simulations, without significantly increasing the computational effort. Over the last years, we have gained experience in hydrodynamic modelling using subgrid based methods [i.e. Defina(2003), Casulli (2009), Volp et al (2013) ]. These methods combine coarse computational grids with high resolution information. In Volp et al (2013 ) we presented a subgrid based, two-dimensional, depth averaged hydrodynamic model, that is inspired by the method presented by Casulli (2009 ). The model makes use of two grids: a (coarse) computational grid and a high resolution subgrid, see Figure 1. The system of equations is solved at the coarse grid, but high resolution information is taken into account. The water level is assumed to be uniform within a computational cell, but the bed and the roughness are allowed to vary within a cell. Therefore, high resolution effects can be taken into account for the computation of cross-sectional areas, cell volumes, advection and friction. This also implies that cells can be wet, partly wet or dry. The solution based on a coarse computational grid improved significantly, when high resolution effects are taken into account. This result is obtained without a significant increase in computational cost.Environmental Fluid Mechanic

Spatial Variations of Antarctic Intermediate Water in the Caribbean Sea Due To Vertical Mixing Along Its Path

Because of its pronounced fresh signature, the properties of the northward-flowing Antarctic Intermediate Water (AAIW) affect the Atlantic Meridional Overturning Circulation. Hence, understanding modifications of AAIW along its path is important. Here, we analyze AAIW changes along its path in the Caribbean Sea and assess whether vertical fluxes from background turbulence and from double-diffusive mixing in thermohaline staircases can explain these variations. We deduce the occurrence rate of staircases (7%) and estimate the flux ratio (Formula presented.) from Argo float profiles. In combination with vertical fluxes from background turbulence, these values are used in a steady-state advection-diffusion model to estimate the effective diffusivity of salt that arises from double diffusion (Formula presented.). This value for (Formula presented.) is similar to observed values (Schmitt, 2005, https://doi.org/10.1126/science.1108678), implying the observed modification of AAIW in the Caribbean Sea may be attributable primarily to vertical mixing in the region itself.Environmental Fluid Mechanic

Hydrodynamics in the mid-field plume region of the Rhine ROFI

River plumes, also regions of freshwater influence , are important features to understand because of their impact on the current structure, stratification and the transport of fine sediments, nutrients and contaminants. One important river plume is the Rhine ROFI. Prior studies have sought to understand far-field dynamics where cross-shore straining is dominant (Simpson & Souza, 1995; Souza & Simpson,1995; De Boer et al., 2008). However, less is known about the mid-field region of this river plume, where fronts matter as well. Here we use field observations from a 6 week measurement campaign in fall 2014 to investigate the dynamics of the mid-field region of het Rhine ROFI. We will focus on the interaction between far-field processes, such as tidal straining, and near field processes, such as fronts. The Rhine ROFI is of interest because the Dutch coast has been modified by extending the Port of Rotterdam and the construction of the Sand Engine that extends into the southern North Sea. These perturbations might impact the currents, the ROFI and the distribution of fine sediment, nutrients and contaminants. Therefore, the understanding of this is of importance. During September and October 2014, a large field observational campaign was conducted off the Dutch coast close to the sand Engine, 10 km north of the river outflow. Measurements were made at two locations, 2 and 5.5 km offshore (see Figure 1). Moorings, with Conductivity Temperature Depth (CTD) and Optical Backscatter (OBS) instruments at different depths, were deployed to obtain vertical profiles of salinity and suspended sediment concentrations (SSC). In addition, at each location a bottom-mounted Acoustic Doppler Current Profiler (ADCP) measured vertical velocity profiles. Radar images of the area were used to gain surface information, specifically about frontal propagation in the vicinity of the measurement locations. The weather conditions were highly variable during the six week period. There were very calm periods, but also storms, which completely destroyed stratification. The wind direction changed during the campaign as well. In addition to the data, numerical modelling with a 3D hydrostatic model will be used to gain information of the entire mid-field plume.Environmental Fluid Mechanic