Improving Global Surface and Internal Tides through Two-Way Coupling with High Resolution Coastal Models
Lead PI: Maarten Buijsman, University of Southern Mississippi
In recent years much progress has been made with implementing, validating, and improving tides in global HYCOM. However, the root-mean square errors between predicted and observed tides in the north Atlantic remain much larger than in other ocean basins. These errors may be attributed to complex coastal shelf geometry on the Hudson and European shelves that is poorly resolved in 1/12º and 1/25º global HYCOM. The north Atlantic has strongly resonant tides that are very sensitive to coastal geometry. The tides near the coast are impacted by the incoming tides from the deep ocean. Additionally, the resonant tides over the shelf impact the deep ocean tides. To improve the surface tides, and implicitly the baroclinic tides, we propose to apply high-resolution coastal models that are nested in the coarser parent HYCOM model through a two-way coupling with the “Adaptive Grid Refinement In Fortran” package. The work highlighted in this proposal is a collaborative effort between the University of Southern Mississippi, the University of Michigan, and the Naval Research Laboratory.
Number of Years: 3
Start Year: 2015
End Year: 2018
Partners:
- Naval Research Laboratory – Stennis Space Center
- University of Michigan, Ann Arbor
Modeling Intrinsic Variability and Connectivity in Shelf and Littoral Circulation
Lead PI: Professor James McWilliams, Department of Atmospheric and Oceanic Sciences, UCLA
The objectives in this research will be discovering and understanding the physical phenomena in the transition zone between shelf and surf currents (inner shelf), the outer shelf, and the upper continental slope with the existing Regional Oceanic Modeling System (ROMS) and then utilizing the model results to guide and interpret the Inner Shelf DRI field measurements. The model comprises oceanic currents, atmospheric coupling, tides, and surface gravity waves. A dual approach is proposed. The focus is on intrinsic variability (eddies) rather than wind and tide forced responses. One research branch is to simulate realistic shelf regimes at several different sites over extended intervals to encounter a variety of forcing conditions and spontaneous realizations. The other branch is to solve idealized problems that simplify and isolate various dynamical processes to determine their influences on the resulting phenomena and to test theoretical ideas. A technical component is testing the global HYCOM model product as a parent data set for downscaling in nested-grid regional subdomains.
Number of Years: 3
Start Year: 2015
End Year: 2018
Partners:
- Scripps Institute of Oceanography
- University of Michigan
- Kobe University, Japan
- LEGOS, Toulouse, France
Linking Surf Zone to the Inner-Shelf: Parameterizing Breaking-Wave Eddy Forcing and Effects of Transient Rip Currents
Lead PI: Falk Feddersen, Scripps Institution of Oceanography
The U.S. Navy’s goal is to to seamlessly forecast from the deep ocean, across the entire continental shelf to the shoreline. To accomplish this, the relevant surfzone and inner-shelf variability must be accounted for either by inclusion of the appropriate physics or by parameterization. Surfzone breaking waves generate vertical vorticity on the scales of 10-20 m, leading to surfzone eddies and transient rip current ejections on 50–100 m scales. Rip current variability at these length-scales is ubiquitous on the inner-shelf, as seen in both airborne inner-shelf dye and temperature measurements. This results in thermal and material exchange between the surfzone and inner shelf and onto the mid-shelf. Only wave-resolving models (e.g., funwaveC) represent finite-crest length wave breaking that generates surfzone eddies and transient rip currents, but do not include important shelf physics (stratification or vertically sheared currents). Wave- averaged models (e.g., Delft3D, NearCom, COAWST) include appropriate shelf physics but cannot generate surfzone eddies leading to transient rip currents. First results from direct coupling of wave-resolving and wave-averaged models (funwaveC & COAWST) demonstrate the strong effects and feedbacks that transient rip currents have on inner-shelf stratification. However, direct coupling is highly inefficient and parameterizations must be developed to allow small scale eddy generation to be represented in wave-averaged models. The overall project objectives are to develop and test parameterizations for surfzone eddy generation driven by finite-crest wave breaking (on 10–20 m scales) due to a directionally spread wave field. This will allow wave-averaged models that include stratification and vertically sheared currents (such as COAWST or Delft3D) to incorporate transient rip current effects on the inner-shelf. PI Feddersen is the funwaveC developer, which has been validated against field observations in a variety of applications including runup, alongshore currents, and surfzone eddy structure. From the wave-resolving funwaveC results, the surfzone eddy forcing mechanism will be parameterized for use in wave-averaged models.
Number of Years: 3
Start Year: 2015
End Year: 2018
Partners:
- UCLA
- University of Michigan
- Stanford University
- The University of Southern Mississippi
Arctic Shelf and Large Rivers: Seamless Nesting in Global HYCOM
Lead PI: Eric Chassignet, Florida State University
Fresh water inputs such as rivers and ice melt are poorly represented in global HYCOM since many of the processes associated with river plume dynamics and ice melt are unresolved. The main scientific and technical objective of the proposed work is to implement river mass flux and temperature flux boundary conditions, as well as two-way nesting to improve the representation of large river plumes and Arctic Ocean ice melt water runoff (land ice and glacier) in global HYCOM and to improve the predictability in coastal regions, the Arctic Ocean, and the Atlantic Ocean. To assess the fidelity of the inner nests and boundary conditions, we will compare our simulations to all available observations. Emphasis will be placed on the fresh water plume dynamics and offshore circulation dynamics, as well as how the rivers impact the seasonal ice melt. We anticipate that the more accurate treatment of the river inflow and embedded two-way nested higher resolution local models will translate into improved river plume dynamics and better HYCOM forecasting skills on the Arctic shelves.
Number of Years: 3
Start Year: 2015
End Year: 2018
Partners:
- Naval Research Laboratory – Stennis Space Center
FY 2016 PI Report
Additional Reports
Oceanic Energy Cascade from Global to Regional Predictive Models
Lead PI: Bruce Cornuelle, Scripps Institution of Oceanography
Understanding the cascade of energy injected into the ocean is crucial to developing our knowledge of ocean predictability and dynamics. Steep ridges, islands, and atolls in the ocean scatter waves and convert energy at a variety of scales, from long Rossby waves through mesoscale, sub-mesoscale, and internal waves. This energy injected at the steep ridges has significant implications for global and regional ocean prediction. Models with insufficient resolution, or which lack the physics of the energy cascade will miss the topographic effects and suffer a drop in predictive skill. These localized effects may play an important role in the basin-wide circulation that is currently predicted by the Navy’s global HYCOM/NCODA system.
The ONR-funded FLow Encountering Abrupt Topography (FLEAT) project aims to understand how the ocean is altered by steep ridges and islands at the full range of length scales in the western tropical Pacific region encompassing Palau and Guam. In cooperation with this project, we will use models to examine how the cascade of energy and enstrophy due to topography impact global and regional predictive skill in the FLEAT region, with a focus on the Navy HYCOM model. We will use a state-of-the-art numerical model and advanced state estimation techniques to reproduce the flows in the FLEAT region by fitting the ocean circulation models to observations. Our goal is to examine the effects of local energy conversion at and near ridges, how the enstrophy affects local ridge processes, and how the energy cascade affects lower wavenumbers away from the ridge in the open ocean.
Number of Years: 3
Start Year: 2015
End Year: 2018
Partners:
- University of Hawaii
- Naval Research Laboratory – Stennis Space Center
- Massachusetts Institute of Technology
FY 2016 PI Report
Additional Reports
Russian Dolls: Nesting a Turbulent Large Eddy Simulation within a Nonhydrostatic Adaptive Grid Model within a 1/25 HYCOM Model
Lead PI: Alberto Scotti, University of North Carolina at Chapel Hill
The goal of this project is to develop a modeling framework capable of spanning, in a localized region, the O(Km) scales where forcing is applied to the O(10 m)$ scales where standard LES SGS models are expected to apply. This is achieved by nesting within HYCOM a non-hydrostatic model based on Adaptive Mesh Refinement, the Stratified Ocean Model with Adaptive Refinement (SOMAR), which in turns drives within selected regions a Large Eddy Simulation (LES) model.
Number of Years: 3
Start Year: 2015
End Year: 2018
Partners:
- Naval Research Laboratory – Stennis Space Center
Seamless Multiscale Forecasting: Hybridizable Unstructured-mesh Modeling and Conservative Two-way Nesting
Lead PI: Pierre Lermusiaux, Massachusetts Institute of Technology
One of our research thrusts is to derive and apply advanced techniques for multiscale modeling of tidal-to-mesoscale processes over regional domains (nearshore-coastal-basin) with complex geometries including shallow seas with strong tides, steep shelfbreaks with fronts, and deep ocean interactions. On the one hand, our conservative implicit two-way nesting for realistic multi-resolution modeling has enabled such high-fidelity coupled multiscale dynamics studies. On the other hand, a high-order multi-dynamics modeling capability based on novel hybridizable discontinuous Galerkin (HDG) numerical schemes is also promising for seamless conservative multi-resolution forecasting. Our overall goal for this NOPP project is to improve, utilize and verify: (i) HYCOM downscaling schemes and conservative two-way nesting schemes for seamless multiscale forecasting and dynamical analyses of realistic coupled physics at abrupt topography; and, (ii) high-order non-hydrostatic HDG schemes for high-fidelity, conservative, and efficient multi-dynamics modeling.
Number of Years: 3
Start Year: 2015
End Year: 2018
Partners:
- Naval Research Laboratory
A Multiscale Nested Modeling Framework to Simulate the Interaction of Surface Gravity Waves with Nonlinear Internal Gravity Waves
Lead PI: Oliver Fringer, Stanford University
We are developing a multiscale nested modeling framework that simulates, with the finest resolution being centimeter scale, surface mixed layer processes arising from the combined action of tides, winds and mesoscale currents with an emphasis on the interaction of surface and internal gravity waves. We will focus on understanding the interaction of surface and internal gravity waves in the South China Sea. Our objective is to study surface gravity wave evolution and spectra in the presence of surface currents arising from strongly nonlinear internal gravity waves. We will focus on understanding the impact of tidal, seasonal, and mesoscale variability of the internal wave field and how it impacts the surface waves.
At the finest scale, a large-eddy simulation (LES) code that simulates turbulence-wave interactions on a wave-surface-fitted grid and a nonlinear wave-field simulation code will be employed. This code will be driven by currents from a high-resolution, nonhydrostatic, isopycnal-coordinate model based on SUNTANS that will simulate nonlinear internal gravity wave evolution in the South China Sea. Initial and boundary conditions for the SUNTANS model will be obtained from the NRL East Asian Seas Nowcast/Forecast System (EASNFS), which computes the generation of internal tides with assimilated seasonal and mesoscale variability. The low-frequency variability from EASNFS will be assimilated into the SUNTANS model using a novel scale-separation technique that assimilates low-frequency data without compromising high-frequency variability related to internal waves. Since EASNFS is also nested within the Global NCOM model, the proposed work will simulate surface-internal wave interactions through nesting of four models over spatial scales ranging from 1000 km down to 10 cm.
Number of Years: 3
Start Year: 2015
End Year: 2018
Partners:
- University of Minnesota
- Naval Research Laboratory – Stennis Space Center