On Ripples - A Boundary Layer-Theoretical Definition

Once the first initial ripples have developed, they form according to the actual flow forces and sediment properties. In this paper, a semianalytical approach to determine the length of the developed ripples is presented. The theory assumes initial disturbances at the bed surface and corresponding flow separations resulting from an individual respective boundary layer. What causes the initial rhythmic perturbations is not the subject of this paper. Based on boundary layer theory, this approach explains a possible physical background for the existence and length of developed ripples in cohesion-free sediments. At the same time, the approach provides a distinction from dunes: ripples are sand waves affected by a viscous sublayer, and dunes are sand waves where this is not the case. Applications to Earth, Mars, and Titan are shown

Usporedba ALADIN i IFS Modela brzine vjetra preko Jadrana

The wind output from atmospheric models is instrumental in forcing the oceanic models. Here we consider the wind output from the ALADIN and IFS models and compare it with the results of scatterometer and altimeter estimates of wind speed over the Adriatic Sea, as well as with the field data from 18 meteorological stations and a gas rig platform. A five-year period from 2008 to 2012 is considered in the comparison. Our principal conclusion is that, overall, both atmospheric models, when compared to the altimeter data, give very similar statistical results, with a scatter index of 0.33 and 0.35 for IFS and ALADIN respectively. More specifically, the ALADIN appears to be better in the Northern Adriatic whereas the IFS seems superior in the Southern Adriatic. A possible explanation of this difference could be that the higher spatial resolution of ALADIN is crucial in resolving the bora wind impact over the Northern Adriatic.Vjetar dobiven atmosferskim modelima je instrumentalan u prisiljavanju oceanskog modela. U ovom radu razmotrit će se vjetra dobiven Aladin i IFS modelima te će se usporediti s rezultatima skat -erometrijske i altimetrijske procjene brzine vjetra iznad Jadranskog mora, kao i s 18 meteoroloških postaja i plinske platforme u razdoblju 2008-2012. Glavni zaključak je da oba atmosferska modela, u usporedbi s podacima altimetrije, daju vrlo slične statističke rezultate, s indeksom raspršenja 0,33 za IFS i 0,35 za ALADIN. Čini se da ALADIN daje bolje rezultate za sjeverni Jadran, a IFS za južni Jadran. Moguće objašnjenje te razlike može biti veća prostorna rezolucija ALADIN-a koja je presudna u rješavanju utjecaja bure na sjevernom Jadranu

Tide-surge-wave modelling and forecasting in the Mediterranean Sea with focus on the Italian coast

Abstract A tide-surge-wave modelling system, called Kassandra, was developed for the Mediterranean Sea. It consists of a 3-D finite element hydrodynamic model (SHYFEM), including a tidal model and a third generation finite element spectral wave model (WWMII) coupled to the hydrodynamic model. The numerical grid of the hydrodynamic and wave models covers the whole Mediterranean with variable resolution. The comparison with coastal tide gauge stations along the Italian peninsula results in a root sum square error for the main tidal components equal to 1.44 cm. The operational implementation of the Kassandra storm surge system through the use of a high resolution meteorological model chain (GFS, BOLAM, MOLOCH) allows accurate forecast of total water level and wave characteristics. The root mean square error for the first day of forecast is 5 cm for the total water level and 22 cm for the significant wave height. Simulation results indicate that the use of a 3-D approach with a depth-varying loading factor and the inclusion of the non-linear interaction between tides and surge improve significantly the model performance in the Italian coast

A fully coupled 3D wave-current interaction model on unstructured grids

We present a new modeling system for wave-current interaction based on unstructured grids and thus suitable for very large-scale high-resolution multiscale studies. The coupling between the 3D current model (SELFE) and the 3rd generation spectral wave model (WWM-II) is done at the source code level and the two models share same sub-domains in the parallel MPI implementation in order to ensure parallel efficiency and avoid interpolation. We demonstrate the accuracy, efficiency, stability and robustness of the coupled SELFE-WWM-II model with a suite of progressively challenging benchmarks with analytical solution, laboratory data, and field data. The coupled model is shown to be able to capture important physics of the wave-current interaction under very different scales and environmental conditions with excellent convergence properties even in complicated test cases. The challenges in simulating the 3D wave-induced effects are highlighted as well, where more research is warranted

Very high resolution flash flood simulation for urban areas based on a fully coupled modeling concept

EGU General Assembly 201

A global unstructured, coupled, high-resolution hindcast of waves and storm surge

Accurate information on waves and storm surges is essential to understand coastal hazards that are expected to increase in view of global warming and rising sea levels. Despite the recent advancement in development and application of large-scale coastal models, nearshore processes are still not sufficiently resolved due to coarse resolutions, transferring errors to coastal risk assessments and other large-scale applications. Here we developed a 50-year hindcast of waves and storm surges on an unstructured mesh of >650,000 nodes with an unprecedented resolution of 2-4 km at the global coast. Our modelling system is based on the circulation model SCHISM that is fully coupled with the WWM-V (WindWaveModel) and is forced by surface winds, pressure, and ice coverage from the ERA5 reanalysis. Results are compared with observations from satellite altimeters, tidal gauges and buoys, and show good skill for both Sea Surface Height (SSH) and Significant Wave Height (Hs), and a much-improved ability to reproduce the nearshore dynamics compared with previous, lower-resolution studies. Besides SSH, the modelling system also produces a range of other wave-related fields at each node of the mesh with a time step of 3 hours, including the spectral parameters of the first three largest energy peaks. This dataset offers the potential for more accurate global-scale applications on coastal hazard and ris

Simulating storm surge and compound flooding events with a creek-to-ocean model: Importance of baroclinic effects

We present a creek-to-ocean 3D baroclinic model based on unstructured grids that aims to unite traditional hydrologic and ocean models in a single modeling platform, by taking full advantage of the polymorphism (i.e. a single model grid can seamlessly morph between full 3D, 2DV, 2DH and quasi-1D configurations). Using Hurricane Irene (2011)\u27s impact on the Delaware Bay as an example, a seamless 2D-3D model grid is implemented to include the entire US East Coast and Gulf of Mexico with a highly resolved Delaware Bay (down to 20-m resolution). The model is forced by flows from a hydrological model (National Water Model ) at the landward boundary. We demonstrate the model\u27s accuracy, stability and robustness with the simulation of the storm surge and subsequent river flooding events and compound surges. Through a series of sensitivity tests, we illustrate the importance of including in the simulation the baroclinic effects, as provided by the large-scale Gulf Stream, in order to correctly capture the adjustment process following the main surge and the subsequent compound flooding events. The baroclinicity can explain up to 14% of the elevation error during the adjustment phase after the storm