Nested Grid System Research Articles

Simulation of the Mediterranean tsunami generated by the Mw 6.0 event offshore Bejaia (Algeria) on 18 March 2021

SUMMARY On 18 March 2021 an earthquake of magnitude Mw = 6.0 occurred offshore the Algerian coasts and generated a tsunami with offshore amplitudes smaller than a few millimetres crossing the western Mediterranean Sea. The objective of this study is threefold: first, to determine whether seismic sources calculated in the context of tsunami early warning are relevant; secondly, to determine whether tsunami simulations are able to reproduce tide-gauge observations and thirdly, to define the sensitivity of simulations to the grid resolutions and tsunami parameters. In the Mediterranean Sea, a very small number of available coastal tide gauges recorded the tsunami. Among them, a few French tide gauge stations recorded water waves with amplitudes smaller than a few centimetres and with periods ranging from 5 to 20 min associated to harbour or bay resonances. Numerical simulations of the tsunami are performed by the operational code Taitoko for seven different source fault models. Three of them allow for a rapid source detection and characterization in the framework of tsunami warning at CENALT (Centre National d'Alerte aux Tsunamis, France). The integrated code Taitoko uses a system of multiple nested grids. Standard Boussinesq equations are solved in the Mediterranean grid, whereas non-linear shallow water equations are solved in coastal and harbour grids with 25 and 5 m resolutions, respectively. Whatever the fault model, the observed time-series of water heights are reproduced satisfactorily both in phase and amplitude by the model at Nice and Monaco but poorly at Port Mahon (Minorca) and Toulon.

Preliminary study of tsunami simulations on megathrust earthquake scenarios in Pacitan Regency, East Java

During the period 1600 to 2007 there have been approximately 109 tsunamis in Indonesia with 90% caused by tectonic earthquakes. Pacitan located in an east java segment subduction area which is very prone to earthquakes and tsunamis. The coastal morphology of Pacitan has great potential for tsunami hazard. This research is focused on conducting numerical modeling of the tsunami generated by the hypothetical megathrust earthquake in the East Java segment with a magnitude of Mw 8.7. The method used is Cornell-Multi Grid Coupled applied shallow water equation with COMCOT 1.7 software. The nested grid system uses 4-layer consisting of 1-layer GEBCO, 2-layer bathymetry, and 1-layer integration of bathymetry and topography to produce tsunami modeling with high resolution. The results showed that the megathrust hypothetical earthquake scenario for the East Java segment caused a vertical displacement at sea level of -4.599 m to 7.019 m. The tsunami propagation northwards towards the Pacitan coast had a maximum amplitude of 33.16 m with a travel time of 23 – 29 minutes and then spreads in all directions. The farthest inundation range occurred in Pacitan Subdistrict as far as 4.189 km to the north of Ranuharjo Beach, while the maximum run-up of 21.82 m occurred in Soge Beach, Ngadirojo Subdistrict. The farthest affected area of inundation occurs on a gently sloping morphology with a slope of 0-8%, the highest run-up is on a moderate to steep sloping morphology with a slope of more than 25%. The results of tsunami simulation can be used for planning tsunami disaster mitigation in Pacitan.

Development of a computational fluid dynamics model adopting a nested grid system: Flow simulations for ideal and real urban settings

We incorporate a nested grid system into a computational fluid dynamics (CFD) model based on the Reynolds-averaged Navier-Stokes equations. First, we evaluate the CFD model by comparing the results simulated in an array of aligned buildings using one- and two-way nested and non-nested coarse (same grid size as the parent domain) and fine grid (same grid size as the child domain) systems. The two-way nested grid simulates double-eddy circulation, wind speeds, and turbulence kinetic energy (TKE) in a street canyon better than the one-way nested grid. The nested simulations produce similar results to the fine grid system but with a significantly reduced CPU time. We also apply the nested grid system to airflow simulations in a building-congested district and validate the simulated results against the wind speed and direction measured by an automated weather system. The nested simulation improves wind direction compared to the WRF model operated by the National Institute of Environmental Research of South Korea. The two-way nested grid successfully reproduces the measured wind speed. The two-way nested grid simulation well represents the continuous flow structure (a smooth flow transition) between the parent and child domains by considering the two-way flow interaction between the two domains.

A high-fidelity parametric model for tropical cyclone boundary layer wind field by considering effects of land cover and terrain

The proper simulation of the tropical cyclone (TC) boundary layer wind field is essential to predict the maximum wind speed, the imposed wind loading on civil structures, and the related potential disasters. A high-fidelity parametric model is developed to produce the wind field and to study the wind characteristics of TCs in the boundary layer. This model adopts a widely used boundary layer turbulence closure scheme and is built on a terrain-following coordinate system, which can consider various land cover and terrain effects. To improve the computational efficiency, a nested grid system is adopted. The developed model is implemented to reproduce the wind fields of Hurricane Isabel (2003), Hurricane Katrina (2005), Hurricane Irene (2011), Typhoon Hagupit (2008), Typhoon Hato (2017), and Typhoon Mangkhut (2018). Different types of observation datasets are used to validate the developed model, including the Hurricane Research Division's H*Wind snapshots, the National Data Buoy Center's wind records, and several meteorological sounding stations' observations. The spatial wind fields and the wind speed time series are presented. The influence of land cover and terrain on the behavior of TC is investigated. The simulation results demonstrate the high-fidelity and computational efficiency of the developed model, implying its potential applications for TC hazard modeling.

High-Resolution Flow Simulations Around a Steep Mountainous Island in Korea Using a CFD Model with One-way Nested Grid System

High-Resolution Flow Simulations Around a Steep Mountainous Island in Korea Using a CFD Model with One-way Nested Grid System

Model sensitivity experiments on data assimilation, downscaling and tides for the representation of the Cape São Tomé Eddies

The impacts of data assimilation, downscaling, and tidal forcing were investigated with focus on the representation of the Cape Sao Tome Eddy (CSTE). Sea level anomaly (SLA), sea surface temperature (SST), and temperature and salinity (TS) profiles were assimilated into a HYCOM nested grid system composed by three grids with horizontal resolutions from 1/4° to 1/24°. Tides were included in the highest resolution domain, which covers the Brazil Current (BC) northern region. Sensitivity experiments were conducted using the high-resolution domain when each observation type was assimilated alone and all together. In addition, the non-tidal and mid-resolution (1/12°) assimilative models were used in the comparison to evaluate the impacts of tides and downscaling. All assimilated observations positively contributed to reducing the temperature errors in the upper 500 m. However, the salinity was degraded in these depths by the assimilation of SST and SLA alone. Assimilation of all observations together decreased T and S errors by 34% and 17%, respectively, as well as raised (and reduced) in 77% (60%) the correlation (deviation) of SLA (SST) between remotely sensed observations when compared to the control run without assimilation. Six observed eddies were objectively compared against the simulated eddies using an eddy tracking algorithm. Downscaling to the higher resolution model was crucial to better represent the observed eddies, as well to increase the simulated energetic levels in the studied region. The inclusion of tides improved the turbulent kinetic energy levels and the CSTE SLA amplitude simulation. SLA data assimilation is of utmost importance for the representation of the CSTE. However, the assimilation of SST and mostly TS was also relevant for correcting the thermohaline field and enabling the correct eddy translation. Finally, possible mechanisms were discussed to explain the CSTE northward migration, against the BC main flow.

Development and Validation of a Tsunami Numerical Model with the Polygonally Nested Grid System and its MPI-Parallelization for Real-Time Tsunami Inundation Forecast on a Regional Scale

We have developed a new numerical model suitable for rapid and wide-area estimation of tsunami inundation and damage. The model is based on the world-renowned TUNAMI code solving the two-dimensional nonlinear shallow water equations, and enables one-stop simulation of the initial tsunami distribution based on a fault model, tsunami propagation and inundation, and damage estimation. It extends the configuration of the grid system from conventional rectangular regions to polygonal regions so that deployment of high-resolution grids can be confined to the coastal lowland, resulting in remarkably improved efficiency in computation and better precision. For the purpose of real-time implementation of tsunami inundation simulation using a high-performance computing infrastructure, vectorization and MPI parallelization have also been conducted. Moreover, the model was verified and validated through several benchmark problems that the National Tsunami Hazard Mitigation Program, organized by federal agencies and states in the U.S., developed as the quality standards for simulating and assessing tsunami hazard and risk. The newly-developed model is named “Real-time Tsunami inundation (RTi) model,” and its computational performance was examined using the SX-ACE, a vector supercomputer installed at Tohoku University. The results show that it requires only 128 cores of the SX-ACE for implementing six-hour tsunami inundation simulation with a 10-meter grid resolution within 10 minutes for the 700 km long coastline of Kochi Prefecture, Japan. This means that the RTi model is over 10 times more efficient as the conventional tsunami model with the rectangular domains, and it can be inferred that 2,451 cores of the SX-ACE are the overall computational resources needed for real-time tsunami inundation forecast on the whole coastal regions along the Nankai Trough subduction zone, corresponding to the computational performance of 170 Tflop/s. The resources required are equivalent to 24% of all the SX-ACE resources at Tohoku University, indicating the feasibility of real-time tsunami inundation forecast on a regional scale by using the RTi model. Since the Disaster Information System operated by the Cabinet Office of the Japanese Government adopted a function of tsunami damage estimation using the aforementioned numerical model, at the end of this paper, a brief overview of the subsystem for rapidly estimating tsunami damage on a regional scale is described.

Evaluation of a high-resolution wave hindcast model SWAN for the West Mediterranean basin

This study aims to present an evaluation and implementation of a high-resolution SWAN wind wave hindcast model forced by the CFSR wind fields in the west Mediterranean basin, taking into account the recent developments in wave modelling as the new source terms package ST6. For this purpose, the SWAN model was calibrated based on one-year wave observations of Azeffoune buoy (Algerian coast) and validated against eleven wave buoys measurements through the West Mediterranean basin. For the calibration process, we focused on the whitecapping dissipation coefficient Cds and on the exponential wind wave growth and whitecapping dissipation source terms. The statistical error analysis of the calibration results led to conclude that the SWAN model calibration corrected the underestimation of the significant wave height hindcasts in the default mode and improved its accuracy in the West Mediterranean basin. The exponential wind wave growth of Komen et al (1984) and the whitecapping dissipation source terms of Janssen (1991) with Cds = 1.0 have been thus recommended for the western Mediterranean basin. The comparison of the simulation results obtained using this calibrated parameters against eleven measurement buoys showed a high performance of the calibrated SWAN model with an average scatter index of 30% for the significant wave heights and 19% for the mean wave period. This calibrated SWAN model will constitute a practical wave hindcast model with high spatial resolution (˜3 km) and high accuracy in the Algerian basin, which will allow us to proceed to a finer mesh size using the SWAN nested grid system in this area.

Downscaling of wave climate in the western Black Sea

This study presents the south-west Black Sea wave climatology based on a downscaling approach of a long-term 31-year SWAN model wave hindcast using telescoping nested grids. At all domains the SWAN model is forced with the CFSR winds. Sensitivity tests are conducted on domain size, computational resolutions, the physical formulations and their adjustable coefficients for deep water source terms, time step of non-stationary calculation, and wind forcing for all domains. For each nested grid the physical and numerical settings were determined separately by calibration against wave buoy measurements at six locations (Gelendzhik, Hopa, Sinop, Gloria, Filyos, and Karaburun) in appropriate domains. Model validation is also conducted for the long-term data using the unused measurements in the calibration. Using the calibrated nested models, a 31-year long-term wave hindcast is conducted. Two-hourly sea state parameters of significant wave height (Hm0), wave energy period (Tm-10), spectral period (Tm01), zero-crossing period (Tm02), peak period (Tp), wind speed components, and mean wave direction (DIR) were collected over three sub-grid domains. Using this database normal and extreme wave conditions in the three sub-grid domains were determined. Finally, extreme waves with different return periods were determined and compared with those presented in the Wind and Deep Water Wave Atlas of Özhan and Abdalla (2002).The present study demonstrates the sensitivity of the SWAN model towards different GEN3 physics options and its adjustable whitecapping parameter Cds and time step of the non-stationary calculations. It is shown that the developed wave model set-up with a nested grid system performs quite satisfactorily and storms are also well-captured. This study yields higher extreme waves in the western part of our area of interest and lower extremes in the eastern part in comparison with those of the presently used Wind and Deep Water Wave Atlas.

The impact of ERA-Interim winds on wave generation model performance in the Southern Caspian Sea region

The aim of the present work is to evaluate wind dataset in generation of the wave characteristic along the southern basin of the Caspian Sea (SBC). To achieve this purpose, satellite altimetry data, numerical model results and field measurements were considered for 2011. The mixed re-analysis/forecast wind data from European Center for Medium Range Weather Forecast, ERAI_MIXED, are analyzed. Comparisons are made using altimetry data from CERSAT, mixed re-analysis/forecast GFS datasets (GFS_MIXED) and field observation from two buoys and one ADCP located in SBC. The modeling was carried out using the SWAN model over a composite-overlap nested grid system. The results showed that the ERAI_MIXED underestimated wind data in SBC, similar to other datasets from ECMWF and GFS. However, the simulation results implied that using the same configuration for the wave model, ERAI_MIXED led to superior results compared to GFS_MIXED and ERAI_MIXED-COR. Comparison with limited observation showed that ERAI_MIXED data slightly overestimated the wave height in the offshore station and underestimated it at the nearshore buoy. Finally, model results showed that moderate to low wind speed over the SBC might generate the waves up to 4 m wave height.

Probabilistic mapping of storm-induced coastal inundation for climate change adaptation

This paper describes a probabilistic approach for mapping of coastal flood hazards associated with sea-level rise and storm intensification toward the end of the 21st century. Under the Representative Concentration Pathway (RCP) 8.5, the Coupled Model Intercomparison Project Phase 5 (CMIP5) predicts a 0.6-m ensemble mean of sea-level rise for the Central Pacific from the 1986–2005 to 2081–2100 epochs. Fifty downscaling simulations of the 2080–2099 period from the CMIP5 NCAR-CCSM4 model produce 2492 hurricanes around the Hawaiian Islands. In comparison with a control dataset for the 1980–1999 period, the simulated future hurricanes show a slight increase in number and a northward shift of the tracks toward the Hawaiian Islands. There are 627 hurricanes in the 2080–2099 dataset with potential impact on Oahu, and the top 24 storms selected by wind speed at the urban Honolulu coast define a scenario set for inundation mapping. A suite of spectral wave, circulation, and Boussinesq models in a nested grid system describes generation and propagation of surge and waves across the ocean as well as wave setup and runup at the coast. The interoperable package includes phase-averaged and phase-resolving processes to determine the coastal flood hazards over a range of spatial and temporal scales during a hurricane event. Since the simulated dataset corresponds to a quasi 1000-year period, barring the tail end of the distribution, the suite of inundation scenarios enables definition of flood hazard maps with return periods of up to 500 years or annual exceedance probabilities of 0.2% or greater for climate change adaptation.

Simulating large emitters using CMAQ and a local scale finite element model. Analysis of the surroundings of Barcelona

In this work, we present a novel approach to simulate large emitters in the microscale. The main idea is to combine a nested grid approach and a finite element model to simulate the subgrid scale. The nested grid system consists of the mesoscale meteorological model WRF-ARW, the Air Emission Model of Meteosim (AEMM), and the air quality model CMAQ. The subgrid scale is simulated using an adaptive, Eulerian, non-steady finite element model. The results from the nested grid simulation are used as initial and boundary conditions in the subgrid model, making this approach one-way. A simulation has been carried out in the surroundings of Barcelona, where an important contributor to the sulphur dioxide levels is considered. The simulations were carried out for one episode with high levels of sulphur dioxide. The time period of the simulation was 48 hours with a 24-hour spin-up.

Thirty-four years of Hawaii wave hindcast from downscaling of climate forecast system reanalysis

The complex wave climate of Hawaii includes a mix of seasonal swells and wind waves from all directions across the Pacific. Numerical hindcasting from surface winds provides essential space-time information to complement buoy and satellite observations for studies of the marine environment. We utilize WAVEWATCH III and SWAN (Simulating WAves Nearshore) in a nested grid system to model basin-wide processes as well as high-resolution wave conditions around the Hawaiian Islands from 1979 to 2013. The wind forcing includes the Climate Forecast System Reanalysis (CFSR) for the globe and downscaled regional winds from the Weather Research and Forecasting (WRF) model. Long-term in-situ buoy measurements and remotely-sensed wind speeds and wave heights allow thorough assessment of the modeling approach and data products for practical application. The high-resolution WRF winds, which include orographic and land-surface effects, are validated with QuickSCAT observations from 2000 to 2009. The wave hindcast reproduces the spatial patterns of swell and wind wave events detected by altimeters on multiple platforms between 1991 and 2009 as well as the seasonal variations recorded at 16 offshore and nearshore buoys around the Hawaiian Islands from 1979 to 2013. The hindcast captures heightened seas in interisland channels and around prominent headlands, but tends to overestimate the heights of approaching northwest swells and give lower estimates in sheltered areas. The validated high-resolution hindcast sets a baseline for future improvement of spectral wave models.

Numerical simulation of Pacific water intrusions into Otsuchi Bay, northeast of Japan, with a nested-grid OGCM

A numerical simulation of Otsuchi Bay located on the northeast coast of the Honshu, the largest island of Japan, is conducted, using an ocean general circulation model (OGCM) with a nested-grid system in order to illustrate seasonal variability of the circulation in the bay. Through a year, an anticlockwise circulation is dominant in the bay, as observational studies have implied, although it is modified in the bay-mouth-half of the bay in winter. In addition, there is an intense outflow at the surface layer during spring to autumn, influenced by river water discharge. Intrusion of the Pacific water into the bay is influened by mean circulations, but it is also influenced by baroclinic tides from spring to autumn. Pacific water intrusions affected by baroclinic tides may have an impact on the environment in Otsuchi Bay.

Extreme Waves and Wave Run-up in Halifax Harbour under Climate Change Scenarios

The tendency for rising sea levels, combined with changes in the frequency and intensity of extreme storm events raises the potential for flooding and inundation of coastal locations such as Halifax Harbour, in the context of climate change. In this study, we consider three scenarios for extreme high water levels based on climate change scenarios and estimates for land subsidence, rising mean sea levels, and return period analysis for extreme events (from previous studies). We also investigate the effect of ocean waves on these estimates for extreme high water levels. Because the most damaging storm to make landfall in Nova Scotia over the last century was Hurricane Juan (2003), it was chosen to simulate the extreme case of storm-generated waves and wave run-up in Halifax Harbour. To simulate waves generated by Hurricane Juan, a nested-grid system consisting of two modern state-of-the-art operational wave models was used. High quality winds were used to drive the wave models, and the simulations used recently updated high resolution coastal bathymetry. Observed water elevation changes in Halifax Harbour were used in wave model simulations of Hurricane Juan. The Federal Emergency Management Agency's (FEMA) run-up model is used to estimate wave run-up elevation, which is validated with recorded high water observations along the coastline. Simulated waves and wave run-up elevations for Hurricane Juan suggest that the maximum significant wave heights at the mouth of the Harbour were 9.0 m, and the wave run-up was as high as 2.0 m along the shoreline of Halifax Harbour. In this way, we estimated the impact of waves and wave run-up on extreme high water elevations for three climate change scenarios in Halifax Harbour, under worst-case conditions. The sensitivity of these estimates is analyzed for different water level variations, wave propagation directions and shore slope profiles. [Traduit par la rédaction] La tendance à la hausse du niveau de la mer de pair avec les changements dans la fréquence et l'intensité des événements de tempêtes extrêmes augmentent le risque d'inondation et de submersion à des emplacements côtiers comme le port d'Halifax dans le contexte du changement climatique. Dans cette étude, nous examinons trois scénarios de niveaux de hautes eaux extrêmes basés sur des scénarios de changement climatique et estimations de subsidence du terrain, l’élévation du niveau moyen de la mer ainsi que l'analyse de la période de retour d’événements extrêmes (faite lors d’études antérieures). Nous examinons aussi les effets des vagues de l'océan sur ces estimations de niveaux de hautes eaux extrêmes. Étant donné que la tempête la plus dévastatrice à avoir touché terre en Nouvelle–Écosse au cours du dernier siècle a été l'ouragan Juan (2003), c'est celle-ci que nous avons choisie pour simuler le cas extrême de vagues produites par une tempête et de remontée de vagues dans le port d'Halifax. Pour simuler les vagues produites par Juan, nous nous sommes servis d'un système à grilles imbriquées consistant en deux modèles de vagues opérationnels à la fine pointe de la technologie. Les modèles de vagues étaient pilotés par des données de vent de haute qualité et les simulations disposaient d'une bathymétrie côtière à haute résolution récemment mise à jour. Les changements observés d’élévation de l'eau dans le port d'Halifax ont été utilisés dans les simulations de l'ouragan Juan par les modèles de vagues. Nous utilisons le modèle de remontée des vagues de la Federal Emergency Management Agency (FEMA) pour estimer la hauteur des remontées, qui est validée par rapport aux observations de hautes eaux enregistrées le long de la côte. Les vagues et les hauteurs de remontée des vagues simulées pour l'ouragan Juan suggèrent que la hauteur significative maximale des vagues à l'entrée du port était de 9,0 m et la remontée des vagues atteignait 2,0 m le long de la côte du port d'Halifax. Nous avons de cette manière estimé l'impact des vagues et de la remontée des vagues sur l’élévation des hautes eaux extrêmes pour trois scénarios de changement climatique dans le port d'Halifax dans les conditions les plus défavorables. Nous analysons la sensibilité de ces estimations à divers changements de niveau d'eau, directions de propagation et profils de pente côtière.

Numerical study of surface water circulation around Sekisei Lagoon, southwest Japan

This paper discusses the variability of surface currents around Sekisei Lagoon using a nested grid ocean circulation model. We developed a triple-nested grid system that consists of a coarse-resolution (1/60° or ∼1.85 km) model off Taiwan, an intermediate-resolution (1/300° or ∼370 m) model around the Yaeyama Islands, and a fine-resolution (1/900° or ∼123 m) model of Sekisei Lagoon. The nested grid system was forced by wind and heat flux calculated from six-hourly atmospheric reanalysis data and integrated over the period from May to July 2003. The coarse-resolution model was driven by lateral boundary conditions calculated from daily ocean reanalysis data to include realistic variation of the Kuroshio and mesoscale eddies with spatial scales of ∼500–700 km in the open ocean. The tidal forcing was included in the intermediate-resolution model by interpolating sea level data obtained from a data-assimilative tidal model. The results were then used to drive the fine-resolution model to simulate the surface water circulation around Sekisei lagoon. Model results show that (1) currents inside the lagoon are mainly driven by tide and wind; (2) there exists a strong southwestward current along the bottom slope in the southeast portion of the lagoon; the current is mainly driven by remote mesoscale eddies and at times intensified by the local wind; (3) the flow relaxation scheme is effective in reducing biases along the open boundaries. The simulated currents were used to examine the retention and dispersion of passive particles in the surface layer. Results show that the surface dispersion in the strong open ocean current region is significantly higher than that inside the lagoon.

Storm Surge Hindcasting of Typhoon Maemi in Masan Bay, Korea

Typhoon Maemi crossed the south coast of Korea at 21LST, September 12, 2003, where its storm surge accompanied by high waves and astronomical high tide induced the most severe coastal disaster in Korea. In particular, Masan City facing Masan Bay had the worst damages from the storm surge flooding with the maximum surge height of ∼230 cm recorded at Masan Port. In order to obtain the design surge heights for the coastal structures in Masan City, a hindcasting study of storm surge for Typhoon Maemi was conducted using a fine-scale regional surge model which was connected to the larger scale surge models by a nested grid system. The sea surface pressure and wind fields were computed by a primitive vortex wind model to obtain the input data for the storm surge model. The hindcasted surge heights were compared with the observed surges at Masan Port as well as at the major tide stations on the south coast of Korea. The hindcasted surges were in a good agreement with the observed surges for both the maximum heights and the occurrence times.

The 2004 December 26 Indian Ocean tsunami impact on Sri Lanka: cascade modelling from ocean to city scales

SUMMARY The 2004 December 26 Indian Ocean tsunami severely hit Sri Lanka. Although it was not in the direct path of the initial tsunami waves, the western coast was struck by diffracted waves that caused much damage. The numerical model GEOWAVE is used to compute tsunami generation, propagation and inundation from the earthquake source to the Sri Lankan coast. A nested grid system is constructed to increase the resolution until Galle Bay, on the southwestern coast, where a 20 m-grid is used. The six nested topobathymetric grids are interpolated from ETOPO2 and high resolution data, at sea as onshore. Simulation results are compared with tsunami height data from National Oceanic and Atmospheric Administration (NOAA; US) and Geological Survey & Mines Bureau (GSMB; Sri Lanka). When the grid resolution increases, the discrepancy between the model and the data remains, on average, good, whereas its spread increases. We then conclude that the order of magnitude of the tsunami height is consistent from the 180 m-resolution grid, but the spatial imprecision is too high to locally predict reliable water heights. Nevertheless, the comparison between computed time-series of sea surface elevation at the Colombo tide station and tide-gauge data shows a very good agreement as both amplitude, and arrival time of the first wave are well reproduced. When focusing onshore, the modelled inundation limit is compared with the limit measured in the field. With its a priori setup, computed inundation spreads much farther behind the field limit. We then integrate more accurate nearshore conditions into the model. Non-linear shallow water equations are chosen instead of fully non-linear Boussinesq equations; the bottom friction on land is increased to a much higher value than at sea; the buildings cover and the low tide conditions are taken into account in the DEM. The resulting high resolution simulation agrees better with field data, even if discrepancies are still locally observed in places of DEM imprecision and in a river valley. This simulation, however, demonstrates that taking into account nearshore and onshore features may significantly improve tsunami impact assessment.

Modeling tsunami hazards from Manila trench to Taiwan

The 2006 dual Pingtung earthquake event and the 2004 South Asia tsunami highlighted the potential tsunami hazards from Manila trench. Manila trench is only about 100 km away from Taiwan, therefore one shall punctuate the importance of thorough study on all possible tsunami scenarios for hazard mitigation. Based on the faults parameters issued by USGS and the seismic record from Global CMT, this study creates a hypothetical earthquake tsunami scenario caused by seismic motion at Manila trench. The magnitude of the earthquake is 9.35 ( M w), the total length is 990 km, and the maximum initial free-surface height is 9.3 m. The initial displacement profile is provided in this paper. An open source code, COMCOT, is adopted to perform the simulation of the tsunami propagation, runup, and inundation around Taiwan. Nested grid system and moving boundary technique are adopted to study runup and inundation. The result shows that the maximum wave height is 11 m in southern Taiwan. Serious flooding is observed in the southwest coast of Taiwan. Tsunami inundation is able to reach 8.5 km inlandward. Due to the refraction effect, 8 m wave height is noted in the northeast coast of Taiwan. The detailed tsunami behavior around Taiwan is described in the context.

Effects of small‐scale features and local wind forcing on tracer dispersion and estimates of population connectivity in a regional scale circulation model

A small‐scale model of the Southern California–Northern Baja California coastline has been developed to explore dispersion over the continental shelf, with specific attention to physical parameters pertinent to simulations of larval dispersal and population connectivity. The ROMS simulation employs a nested grid system, with an inner domain resolution of 600 m and an outer domain resolution of 1.5 km. Realistic bathymetry and forcing were employed to investigate the effects of passive transport of tracers introduced at locations with known communities of mytilid mussels along the coastline. The effects of topographic resolution, boundary conditions, and choice of meteorological forcing products on dispersion rates, tracer trajectories, and the subsequent measures of population connectivity were examined. In particular, the choice of wind forcing product resulted in different circulation patterns and tracer trajectories and had especially important consequences on measures of larval connectivity such as self‐seeding, potential for larval settlement (import), and contribution to the pool of available larvae (export). While some forcing products performed better when model data were compared to field measurements, no product was clearly superior. The uncertainty in results, which may appear minor in larger‐scale temperature or surface velocity fields, is significant when examining a sensitive passive tracer. This modeling uncertainty needs to be addressed when interpreting connectivity results.