Coastal Ocean Circulation and biogeochemical modeling Young-Gyu Park Korea Ocean Research and Development Institute

Pollution Fate & Transport Mixed with ambient water How much and how fast? Transported How far, how fast and to where? If you want detailed temporal and spatial distribution, you need a coastal ocean circulation modeling.

Ocean Models Thank to the computer technology, ocean modeling becomes very popular. Commercial products: coastal engineering SMS Public domain: science POM, ROMS, MOM, HYCOM, COHERENS, FVCOM … Your own!

Is an ocean model a black box? It is not easy to know all the detail of a 3D ocean circulation model. Even a developer may not know the whole model except the part he/she developed! Some commercial model could be used as a black box. In most cases one needs to know the basics at least.

Ocean Circulation Model Decompose the domain into boxes Grids Vertical Horizontal Transform the continuous hydrodynamic equations into discrete equations differential difference Calculate velocity, temperature and salinity at each grid point at certain time.

Ocean Circulation Models Benefit 3D structure of ocean circulation and related fields Cheap compared to the observations Parameter (sensitivity) study Process study Optimal analysis of observational results Prediction

Ocean Circulation Models drawback In some cases, different models produce different results. Assumptions Subgrid scale processes: mixing Hard to justify the assumptions in not a few cases. Errors Discretization: Grid size is finite! Uncertainty in the boundary conditions Hard to quantify the error in not a few cases.

Size of Domain

Large scale Ocean Circulation Model Global ocean, Basin Scale, Climate MOM (NOAA/GFDL Modular Ocean Model), POP (Parallel Ocean Program), POM (Princeton Ocean Model), HYCOM, ROMS, MRI model, SOC model … Low horizontal resolution (2-5 degrees) Cannot resolve major boundary currents properly. Unphysically large friction to maintain numerical stability

Large scale Ocean Circulation Model Process oriented Global properties Global long term prediction IPCC reports Global carbon cycle

CO2 Exchange (1765) Global Carbon Cycle Model using MOM and OCMIP CO2 chemistry

Regional Ocean Circulation Model East China Sea, South China Sea Regional processes Regional prediction High horizontal resolution (a few tenth of degree) Resolve important boundary currents POM, ROMS, MOM, HYCOM, FVCOM Open boundary condition

East China Sea Model grid for FVCOM

High resolution modeling Earth Simulator in Japan 1/10 degree horizontal resolution

Coastal Ocean Circulation Model Coastal zones and estuary. Very high resolution (O(10m)) High spatial temporal variability POM, FVCOM, COHERENS, SMS, ADCIRC …

What do we need in a coastal model Fresh water from rivers and ground water Tide & intertidal zone Open boundary: effect of the open ocean Complex geometry: coast line bottom topography Higher accuracy

Grids (coordinate)

Vertical Coordinate Griffies et al

z Coordinate MOM, POP (open ocean) Easy to use Staircase bottom topography real model

r (density) Coordinate HYCOM, HIM (open ocean) Recently developed Water moves along isopycnal surfaces Good physics

s Coordinate POM, ROM, FVCOM (regional and coastal ocean) terrain following Pressure gradient error Mellor et al., 1994

Generalized (hybrid) vertical coordinate Overcome inherent limitations in each coordinate system Z-near surface, s near bottom

Horizontal grid From Chen at UMASSD

From Chen at UMASSD

0.5-4 km 4 km 2 km From Chen at UMASSD

Current Popular Numerical Models 1. Finite-Difference Method (the most popular one): POM (Princeton Ocean Model) ECOM-si (an updated version of POM) ROM (developed by the Rutgers University) Curvilinear coordinate system 2. Finite-Element Method (mainly comes from engineering): QUODDY (developed by the Dartmouth College) Unstructured grids (triangular meshes) From Chen at UMASSD

Difference between Finite-Difference, Finite-Element and Finite-Volume Methods (FDM, FEM, FVM) x Integration Difference Variation From Chen at UMASSD

Integration flux method Variational approach ECOM-si POM and ROM Use the central finite-difference scheme for bottom time integration and space gradients; Two time stepping or mode splitting: a) external mode and b) internal mode; Time and space smoothing (POM) Use the semi-implicit scheme to calculate the surface elevation; Single time stepping No time and space smoothing FVCOM QUODDY Integration flux method Variational approach Models Pro Con Finite-difference Computational efficiency Piece-piece structures Mass conservative (Rectangular grids) Geometric fitting Grid-dependent mass conservation Finite-element Complicated code structure Poor mass conservation Finite-volume Combine advantage of FDM and FEM Ensure mass conservation in individual control volume ?????? From Chen at UMASSD

Popular models

For Large Scale MOM (Modular Ocean Model) NOAA/GFDL (www.gfdl.gov), z-coordinate HIM (Hallberg isopycnal model) NOAA/GFDL (www.gfdl.gov), r-coordinate HYCOM (HYbrid Coordinate Ocean Model) http://oceanmodeling.rsmas.miami.edu/hycom/ Z at the surface, s at the bottom r in the interior

POM Princeton Ocean Model http://www.aos.princeton.edu/WWWPUBLIC/htdocs.pom/ Developed by G. Mellor at the Princeton U. Global, regional, coastal It has been very popular, but since G. Mellor’s retirement the model is not being developed anymore. There are quite a few models originated from POM. ROMS, ECOM, COHERENS

ROMS Regional Ocean Modeling System http://marine.rutgers.edu/po/index.php? Primitive equation s(s)-coordinate model Actively being developed and maintained. Global, regional, coastal (?) Developed by D. Haidvogel at Rutgers U. Circulation, biogeochemistry, sediment, sea ice

FVCOM Finite Volume Coastal Ocean Circulation Model http://fvcom.smast.umassd.edu/ Unstructured (finite volume) s-coordinate primitive equation hydrostatic model Developed by Chen and UMASSD and Beardsley at WHOI Coastal and estuary Ecosystem, water quality, sediment, sea ice modules

Issues in coastal ocean modeling Open boundary conditions tide inflow/outflow and associated tracer transport Inter tidal zone (wet/dry) Fresh water flux Better representation of topography Mixing Verification

Verification of model results Observation Hydrography, satellite … Model intercomparison

Biogeochemical modeling Nutrient cycle, CO2 cycle, Eco system, Water quality In some models (ROMS, FVCOM, COHERENS), there are modules for biogeochemical processes. Interdisciplinary efforts Physical modelers do not have enough knowledge (or interest) on biogeochemistry. Biologists or chemists do not believe hydrodynamic model results.

Eco system model Parameters controlling the interaction between the components 1D model: verify the parameters (stability) Combine with the hydrodynamic model NPZD model From FVCOM manual

Water Quality Model From FVCOM manual

On going Coastal Ocean Modeling Project in Korea

circulation & biogeochemistry management circulation & biogeochemistry KORDI Dept. Environment effect of dyke circulation & biogeochemistry KORDI management circulation & biogeochemistry Under consideration

circulation & biogeochemistry management circulation & biogeochemistry KORDI Dept. Environment effect of dyke circulation & biogeochemistry KORDI management circulation & biogeochemistry Under consideration

East China Sea Modeling Project With help from Prof. Chen at UMASSD Circulation Eco system

Circulation and eco system modeling Current status Effects of Yangtze river discharge Response to the global change Down scaling from IPCC AR4 simulations

Conclusions A (coastal) ocean circulation model with various modules might become a commodity in a few years irrespective of its inherent flaws and limitations. It would be very hard to ignore model or model results. Develop your own or find one serves your purpose best and use it? One could spend a few years to develop his/her own model, but it is very hard to compete against group efforts. A model tends to become more and more complex, and it becomes harder to understand the whole model completely, yet we cannot treat the model as a black box. Collaboration among modelers, chemist, and biologist is crucial, if you want to get useful results. At KORDI, we are trying to model the circulation and the biogeochemistry of the East China Sea and a few coastal areas.

Thank you