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Models coupling with specific focus on ocean physics

Models coupling with specific focus on ocean physics

Special issue: Advances in computational modelling of natural hazards and Research article 12 Aug Correspondence : Jannis M. Hoch j. Fluvial flood events are a major threat to people and infrastructure. Typically, flood hazard is driven by hydrologic or river routing and floodplain flow processes. Since they are often simulated by different models, coupling these models may be a viable way to increase the integration of different physical drivers of simulated inundation estimates.

We then tested the hypothesis that smart model coupling can advance inundation modelling in the Amazon and Ganges basins. Results confirm that model coupling can indeed be a viable way forward towards more integrated flood simulations.

However, results also suggest that the accuracy of coupled models still largely depends on the model forcing. Hence, further efforts must be undertaken to improve the magnitude and timing of simulated runoff. In addition, flood risk is, particularly in delta areas, driven by coastal processes. A more holistic representation of flood processes in delta areas, for example by incorporating a tide and surge model, must therefore be a next development step of GLOFRIM, making even more physically robust estimates possible for adequate flood risk management practices.

Globally, the number of exposed population and assets as well as casualties and economic damage due to flooding increased greatly in recent decades Hirabayashi et al.

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To better predict and understand current and future flood hazard as well as to plan mitigation and adaption measures, several numerical models, so-called global flood models Trigg et al. Current global flood models, however, are tailor-made for certain applications and excel at, for instance, their representation of hydrologic processes, computationally efficient routing, or hydrodynamic surface flow processes. Depending on model structure and workflow, each model therefore has specific advantages and shortcomings.

Also, there are marked differences between the spatial resolutions, affecting both the range of physical processes to be simulated and the applicability of model output maps Beven et al.

Additionally, different physical processes may be governing at different spatial scales. For instance, 1-D hydrodynamics may be appropriate for large-scale or even global applications, explicitly modelling floodplain flow with 1-D and 2-D models can be vital for more local assessments.

Depending on the envisaged application, modelling set-ups must thus be able to reflect the importance of various flood triggers by integrating across the relevant physical processes and spatial scales. Answering the question of how much complexity is needed can have benefits in avoiding not only under-fitting but also over-fitting of the problem Neal et al. For instance, applying higher-order approximations of the shallow water equations may be disproportionate for high-gradient regions where channel flow is the main physical process to consider while it is very much needed if inundation patterns in flat delta areas are simulated.

For simulating physical processes and hazards across spatial scales without adding just another new model, flexible computational frameworks are viable means as they can be designed depending on envisaged application. By providing the flexibility to couple models depending on the application, fit-for-purpose coupled models can be created. For instance, one can address different processes that govern at different spatial and temporal resolutions by nesting local high-resolution 2-D models in large-scale 1-D models only where these processes are relevant.

This is in contrast to other approaches aiming at combining floodplain runoff with river channel routing via predefined lateral inflows Biancamaria et al. To our knowledge, the development and application of flexible model coupling frameworks specifically designed for large-scale coupled hydrologic and hydrodynamic modelling is very limited.

These studies showed that coupling hydrologic processes with more advanced hydrodynamic processes improves both representation of inundation along reaches as well as the simulation of flood wave propagation.

As the coupling framework was, however, still limited to large-scale hydrologic models and local 1-D—2-D hydrodynamic models covering the floodplains, flood-triggering processes outside the domain of the hydrodynamic models might be hampered because of the simplified routing still executed by the hydrologic models.

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Adding a river routing component to the model coupling framework allows for potentially improved flood wave propagation throughout the entire domain Zhao et al. Consequently, it would be possible to create various coupled models with different levels of complexity depending which model and model types are combined for which fraction of the study area.

To assess whether and under which circumstances model coupling is beneficial for yielding improved discharge and inundation extent and how additional layers of complexity may benefit output accuracy, we tested different coupling designs of different complexity. To this end, GLOFRIM was evolved by creating a more modular framework, extending the models contained, providing a plug-and-play tool allowing for spatially explicit coupling of hydrologic and hydrodynamic models. To enhance process and scale integration, we added the global river routing model CaMa-Flood Yamazaki et al.Physics LE is a physics online homework platform that is textbook-independent and affordably priced.

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Grading curves can easily be established to automatically determine a letter grade. The Gradebook can be readily exported in a variety of formats.In fluid dynamicswind wave modeling describes the effort to depict the sea state and predict the evolution of the energy of wind waves using numerical techniques.

These simulations consider atmospheric wind forcing, nonlinear wave interactions, and frictional dissipation, and they output statistics describing wave heightsperiodsand propagation directions for regional seas or global oceans.

Such wave hindcasts and wave forecasts are extremely important for commercial interests on the high seas. For the specific case of predicting wind wave statistics on the ocean, the term ocean surface wave model is used. Other applications, in particular coastal engineeringhave led to the developments of wind wave models specifically designed for coastal applications. During the s and s, much of the theoretical groundwork necessary for numerical descriptions of wave evolution was laid.

For forecasting purposes, it was realized that the random nature of the sea state was best described by a spectral decomposition in which the energy of the waves was attributed to as many wave trains as necessary, each with a specific direction and period. This approach allowed to make combined forecasts of wind seas and swells. The first numerical model based on the spectral decomposition of the sea state was operated in by the French Weather Service, and focused on the North Atlantic.

First generation wave models did not consider nonlinear wave interactions. Second generation models, available by the early s, parameterized these interactions. The wave modeling project WAMan international effort, led to the refinement of modern wave modeling techniques during the decade Wind wave models are used in the context of a forecasting or hindcasting system.

Differences in model results arise with decreasing order of importance from: differences in wind and sea ice forcing, differences in parameterizations of physical processes, the use of data assimilation and associated methods, and the numerical techniques used to solve the wave energy evolution equation.

A wave model requires as initial conditions information describing the state of the sea. An analysis of the sea or ocean can be created through data assimilation, where observations such as buoy or satellite altimeter measurements are combined with a background guess from a previous forecast or climatology to create the best estimate of the ongoing conditions.

In practice, many forecasting system rely only on the previous forecast, without any assimilation of observations.

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A more critical input is the "forcing" by wind fields: a time-varying map of wind speed and directions. The most common sources of errors in wave model results are the errors in the wind field. Ocean currents can also be important, in particular in western boundary currents such as the Gulf Stream, Kuroshio or Agulhas current, or in coastal areas where tidal currents are strong. Waves are also affected by sea ice and icebergs, and all operational global wave models take at least the sea ice into account.

The sea state is described as a spectrum ; the sea surface can be decomposed into waves of varying frequencies using the principle of superposition. The waves are also separated by their direction of propagation. The model domain size can range from regional to the global ocean. Smaller domains can be nested within a global domain to provide higher resolution in a region of interest. The source function has at least three terms: wind forcing, nonlinear transfer, and dissipation by whitecapping.

For intermediate water depths the effect of bottom friction should also be added.

models coupling with specific focus on ocean physics

The output of a wind wave model is a description of the wave spectra, with amplitudes associated with each frequency and propagation direction.

Results are typically summarized by the significant wave heightwhich is the average height of the one-third largest waves, and the period and propagation direction of the dominant wave. Wind waves also act to modify atmospheric properties through frictional drag of near-surface winds and heat fluxes. The European Centre for Medium-Range Weather Forecasts ECMWF coupled atmosphere-wave forecast system described below facilitates this through exchange of the Charnock parameter which controls the sea surface roughness.

This allows the atmosphere to respond to changes in the surface roughness as the wind sea builds up or decays. Physics includes wave field refraction, nonlinear resonant interactions, sub-grid representations of unresolved islands, and dynamically updated ice coverage. Up tothe model was limited to regions outside the surf zone where the waves are not strongly impacted by shallow depths. The model can incorporate the effects of currents on waves from its early design by Hendrik Tolman in the s, and is now extended for near shore applications.

models coupling with specific focus on ocean physics

The wave model WAM was the first so-called third generation prognostic wave model where the two-dimensional wave spectrum was allowed to evolve freely up to a cut-off frequency with no constraints on the spectral shape. The model has been coupled to the atmospheric component of IFS since Wind wave forecasts are issued regionally by Environment Canada.Nicholls, S. The impact of ocean—atmosphere coupling and its possible seasonal dependence upon Weather Research and Forecasting WRF Model simulations of seven, wintertime cyclone events was investigated.

Model simulations were identical aside from the degree of ocean model coupling static SSTs, 1D mixed layer model, full-physics 3D ocean model.

Model simulations produce SST differences of up to 1. Analysis of the storm environment and the overall simulation failed to reveal any statistically significant differences in model error attributable to ocean—atmosphere coupling.

Thus, while 3D ocean model coupling tended to generally produce more realistic simulations, its impact would likely be more profound for longer-term simulations.

Computational power increases have driven the development of increasingly complex numerical weather prediction models, such as the Weather Research and Forecasting WRF Model Skamarock et al. Despite the complexity and land surface coupling abilities of the WRF Model, it lacked any direct ocean—atmosphere coupling functionality until April WRF version 3.

This coupling is vital for tropical cyclone Sutyrin and Khain ; Bender et al. Such dependencies motivate ocean—atmosphere coupled model development. One early study Bender et al.

Wind wave model

Their simulations only varied cyclone propagation speed slow, medium, fast and produced maximum simulated SST coolings of 5. These changes decreased simulated cyclone intensity and maximum winds by up to 7. More recently, Ren et al. Consistent with Bender et al. Using the Ren et al.

models coupling with specific focus on ocean physics

East Coast. As compared to Ren et al. Larger changes in Yao et al. As of WRF version 3. For SST update, SST values are updated at user-prescribed intervals using lower-boundary input files and are otherwise constant. At initialization, standard ocean temperature profiles are affixed to SST values and a uniform, user-selected, mixed layer depth is prescribed over the entire model domain.

During forward integration, atmospheric wind stress is applied to each simulated ocean column, but neither horizontal advection nor transport processes e.We develop and analyze an optimization-based method for the coupling of nonlocal and local diffusion problems with mixed volume constraints and boundary conditions. The approach formulates the coupling as a control problem where the states are the solutions of the nonlocal and local equations, the objective is to minimize their mismatch on the overlap of the nonlocal and local domains, and the controls are virtual volume constraints and boundary conditions.

As a result, the latter provides the groundwork for the development of engineering analysis tools, while numerical results for nonlocal diffusion in three-dimensions illustrate key properties of the optimization-based coupling method. GOV collections:. Title: A coupling strategy for nonlocal and local diffusion models with mixed volume constraints and boundary conditions.

models coupling with specific focus on ocean physics

Full Record Other Related Research. Abstract We develop and analyze an optimization-based method for the coupling of nonlocal and local diffusion problems with mixed volume constraints and boundary conditions.

A coupling strategy for nonlocal and local diffusion models with mixed volume constraints and boundary conditions. United Kingdom: N. Copy to clipboard.

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United Kingdom. Free Publicly Available Full Text. Copyright Statement. Other availability. Search WorldCat to find libraries that may hold this journal. Cited by: 4 works. Citation information provided by Web of Science. LinkedIn Pinterest Tumblr. Similar Records.Regional models were originally developed to serve weather forecasting and regional process studies.

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Typical simulations encompass time periods in the order of days or weeks. Thereafter regional models were also used more and more as regional climate models for longer integrations and climate change downscaling. Regional climate modeling or regional dynamic downscaling, which are used interchangeably, developed as its own branch in climate research since the end of the s out of the need to bridge the obvious inconsistencies at the interface of global climate research and climate impact research.

The primary aim of regional downscaling is to provide consistent regional climate change scenarios with relevant spatial resolution to serve detailed climate impact assessments. Similar to global climate modeling, the early attempts at regional climate modeling were based on uncoupled atmospheric models or stand-alone ocean models, an approach that is still maintained as the most common on the regional scale.

However, this approach has some fundamental limitations, since regional air-sea interaction remains unresolved and regional feedbacks are neglected.

This is crucial when assessing climate change impacts in the coastal zone or the regional marine environment. To overcome these limitations, regional climate modeling is currently in a transition from uncoupled regional models into coupled atmosphere-ocean models, leading to fully integrated earth system models.

Coupled ice-ocean-atmosphere models have been developed during the last decade and are currently robust and well established on the regional scale. Their added value has been demonstrated for regional climate modeling in marine regions, and the importance of regional air-sea interaction became obvious.

Coupled atmosphere-ice-ocean models, but also coupled physical-biogeochemical modeling approaches are increasingly used for the marine realm. First attempts to couple these two approaches together with land surface models are underway. Physical coupled atmosphere-ocean modeling is also developing further and first model configurations resolving wave effects at the atmosphere-ocean interface are now available. These new developments now open up for improved regional assessment under broad consideration of local feedbacks and interactions between the regional atmosphere, cryosphere, hydrosphere, and biosphere.

Keywords: regional climate modelingair-sea couplingregional climate system modelsair-sea interactionregional earth system models. Coupled air-sea models are today state-of-the-art in global climate research and increasingly used for regional climate modeling.

The general aim of this article is to provide an overview of the field of regional coupled air-sea modeling. After a general introduction, the historic development of the field is briefly summarized and model concepts are introduced. Thereafter, major methodological issues and recent advancements are discussed and key scientific challenges are highlighted.

The relevance of air-sea interaction is briefly discussed for selected exemplary case studies and state-of-the-art in the field is explored. Regional coupled air-sea models are increasingly used for climate change downscaling to regional systems.

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The recent progress here is reviewed and key challenges and the added value of regional coupled downscaling vs. Finally an outlook on remaining challenges and future developments is given.

The primary aim of regional modeling was to study the dynamics and feedbacks in regional systems and the need for regional forecasts on timescales of days to weeks resolving finer details. The regional forecast models were thereafter also used in climate research on timescales of months or seasons to years to decades and regional climate modeling developed as its own research field in climate research since the end of the s out of the need to bridge the obvious inconsistencies at the interface of global climate research and the requirement for sufficient details in climate impact research.

Eventually, the field became crucial to serve societal needs in assessment of regional climate change impacts, and regional climate models were employed as standard tools to provide consistent regional scenarios with relevant spatial resolution for detailed climate change assessment. Similar to global climate modeling, the early attempts at regional climate modeling were based on uncoupled atmospheric models and stand-alone ocean models.

The uncoupled models were forced by atmospheric boundary conditions ocean models or sea surface boundary conditions atmospheric models. Uncoupled stand-alone atmosphere or ocean modeling is still the most common approach on the regional scale.Gross, M. Numerical weather, climate, or Earth system models involve the coupling of components. At a broad level, these components can be classified as the resolved fluid dynamics, unresolved fluid dynamical aspects i.

Typically, each component is developed, at least initially, independently. Once development is mature, the components are coupled to deliver a model of the required complexity.

The implementation of the coupling can have a significant impact on the model. As the error associated with each component decreases, the errors introduced by the coupling will eventually dominate. Hence, any improvement in one of the components is unlikely to improve the performance of the overall system.

The challenges associated with combining the components to create a coherent model are here termed physics—dynamics coupling. The issue goes beyond the coupling between the parameterizations and the resolved fluid dynamics.

This paper highlights recent progress and some of the current challenges. It focuses on three objectives: to illustrate the phenomenology of the coupling problem with references to examples in the literature, to show how the problem can be analyzed, and to create awareness of the issue across the disciplines and specializations.

Weather, climate, and Earth system models approximate the solutions to sets of equations that describe the relevant physics and chemistry. These equations represent, for example, balances of momentum, energy, and mass of the appropriate system. Discrete approximations in space and time to these continuous equations are necessary to solve these equations numerically. Creating a single, coherent, and consistent discretization of an entire system of equations covering the entire range of spatial and temporal scales, even for one component such as the atmosphere, is indeed challenging, if not an impossible task.

Even if it is possible, the numerical solution of such a system spanning all possible scales is currently beyond the reach of even the most powerful computers. Therefore, the system is separated into components that are discretized mostly independently of each other and then coupled together in some manner. These components can broadly be classified as comprising the resolved fluid dynamical aspects of the atmosphere or the ocean, unresolved fluid dynamical aspects e.

The challenges associated with bringing together all the various discretized components to create a coherent model will be referred to here as physics—dynamics coupling. Figure 1a schematically shows the variety of model components and the different aspects of discretizing them in both space and time, as well as the coupling between them.