ACRONYM Spell Out Full Name

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Tide Models
The Navy sometimes uses the term tide models to
designate those numerical ocean models being run
primarily for the purpose of predicting tidal
heights and/or currents. At this time, the tide
models used by the Navy are run in a 2D mode (no
variation in the vertical dimension). By
definition these models must include tidal
forcing, but they may also include other types of
forcing, just as other ocean circulation models
used by the Navy may include tidal forcing.
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GFMPL TP

• The GFMPL Tide Prediction program is not an ocean
  model in the sense of the other models discussed
  in this course.
• TP can predict hourly tidal heights at a fixed
  number of reference stations by using tidal
  constants (amplitude and phase) previously
  calculated from measurements made at those
  locations.
• Additionally, it can predict tidal heights at a
  set of secondary stations, by applying known
  corrections to the reference stations.

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• Tidal heights may only be forecast at locations
  for which historical tidal data are available
  (i.e., tide stations provided by the data base).
  
• This method does not account for sea level
  variations due to changes in atmospheric
  pressure, nor those due to wind forcing.
• Tidal currents are not predicted.

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ADCIRCAdvanced Circulation model

• Primary contacts Cheryl Ann Blain (NRL-SSC),
  Steve Haeger (NAVO)
• ADCIRC was developed in the late 1980s to early
  1990s by Rick Luettich (Univ. of N. Carolina)
  and Joannes Westerink (Univ. of Notre Dame) in
  conjunction with the Coastal Engineering Research
  Center (now called the Engineering Research and
  Development Center) of the Army Corps of
  Engineers. It is currently used in a 2D mode by
  NAVO for tidal and surge current and height
  predictions in littoral areas, although in the
  future, tidal currents may only be shown for
  those areas where the currents are dominated by
  tides. A 3D version, though still barotropic, is
  available and a baroclinic version is under
  development.

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ADCIRChttp//www.marine.unc.edu/C_CATS/adcirc/
http//www.nd.edu/adcirc/
ADCIRC is a finite element, free surface
barotropic ocean circulation model. NAVO runs
the 2D version with tidal and wind forcing, for
the primary purpose of predicting sea level
height. While sea level is not strongly
influenced by density structure, currents may be,
so tidal current forecasts are likely to be best
where the water is well-mixed top to bottom.
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Physics

• Shallow water equations, including non-linear
  terms
• The equations have been formulated using the
  traditional hydrostatic pressure and Boussinesq
  approximations. A quadratic form of bottom
  friction is used. Although the drag coefficient
  may vary in space, it is generally specified as
  constant.

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Domain

• Due to the complications in designing and
  implementing an efficient and accurate grid, NAVO
  runs ADCIRC only in a limited number of domains.
  It is technically feasible, but
  personnel-intensive.
• NRL and others are working to implement an
  automated grid generation program so that ADCIRC
  can be rapidly relocated to new geographic areas.
  It is presently being used in a research,
  although not an operational, setting.
• NAVO is currently running ADCIRC for three
  geographic regions the Yellow Sea and Sea of
  Japan the Arabian Gulf and Gulf of Oman and the
  western North Atlantic Ocean including the
  Caribbean, Gulf of Mexico and US Eastern Seaboard.

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Operational ADCIRC Domains
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Grid and Coordinate System

• ADCIRC uses a finite element grid in the
  horizontal.
• ADCIRC may be run in either Cartesian or
  spherical coordinates. NAVO uses spherical
  coordinates.
• Since it is 2D, there is no vertical coordinate.
  The velocities are a depth-average.

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Spatial and Temporal Resolution

• One of the advantages of a finite element grid,
  is that the spatial resolution is continuously
  variable over the domain. Generally it varies
  from a few 10s of meters to several kilometers.
• The model as implemented at NAVO uses a time step
  of 30 seconds.

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Yellow Sea and Sea of Japan
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THE ADVANTAGES OF FINITE ELEMENTS
South Korea
Mississippi River Delta
Realistic coastline morphology
Large domains with remote boundaries
Fine-scale resolution of inter-tidal zones
Western North Atlantic
Courtesy of Cheryl Ann Blain
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Boundary Conditions

• Open boundaries are in water depths gt 1000 m.
• Tidal elevations from the Grenoble tide model (Le
  Provost et al. 1994) are applied on the open
  boundaries.
• While it is an option in ADCIRC, wetting and
  drying along land-sea boundaries is not included
  in the NAVO implementation.
• The condition at the land-sea boundary is no
  normal flow.

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Tidal constituents
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Forcing

• In addition to the tidal elevations applied on
  the open boundaries, astronomical tide generating
  forces are applied over the whole domain.
• Atmospheric pressure and wind stress forcing from
  either NOGAPS (the western North Atlantic Ocean),
  COAMPSTM (the Yellow Sea and Sea of Japan) or a
  combination of the two (Arabian Gulf and Gulf of
  Oman) is used.

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Initialization

• The model is started from rest.
• The density is constant and uniform.
• NAVO generally uses a spin-up time of 3 days
  before results are used.
• A longer spin-up time is desirable. In the
  future, this might be accomplished by changes in
  the implementation, and/or taking advantage of a
  warm start capability after a long initial
  spin-up.

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Data Assimilation

• No data is assimilated into this model.

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Implementation

• Can be executed on all super-computer and
  workstation platforms.
• Computationally efficient.

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Output

• Tidal heights and currents are output at 30-min
  intervals for a 48-hr forecast.
• The numerical output is post-processed to produce
  a graphical format. The graphics generally do
  not show the whole domain, but rather are focused
  on predetermined areas of the grid. This may
  affect how the results are interpreted.

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Following example is from Shatt Al Arab.
NAVO Product Information

• Spatial resolution variable
• Forcing 27 km COAMPS_SW_ASIA winds and
  atmospheric pressure and tidal forcing
• Output available through MVL sea level relative
  to MSL (mean sea level) depth-averaged current
  speed and direction
• Temporal resolution and forecast duration 30
  min. out to 48 h
• Product update cycle 12 h

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Arabian GulfYellow Sea
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References

• Blain, C.A., R.H. Preller, and A.P. Rivera, Tidal
  prediction using the Advanced Circulation Model
  (ADCIRC) and a relocatable PC-based system,
  Oceanography, 15 (1), 77-87, 2002.
• Luettich, R., and J. Westerink, Users Manual
  ADCIRC, A (Parallel) Advanced Circulation Model
  for Oceanic, Coastal and Estuarine Waters,
  http//www.marine.unc.edu/C_CATS/adcirc/, 2000.

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PCTides

• Primary contacts Ruth Preller, NRL-SSC
• Over the past 3 years, NRL has developed a
  globally relocatable tide/surge prediction
  capability, designed for use on or near
  continental shelves.
• The capability is utilized for locations where
  neither observations nor a regularly run
  operational tide prediction model, such as
  ADCIRC, exists. (Blain et al. 2002).

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PCTideshttp//www7320.nrlssc.navy.mil/pctides/

• PCTides is the NRLs globally relocatable
  tide/surge forecast system used for the rapid
  prediction of tidal amplitude and phase, as well
  as barotropic ocean currents.
• There are 2D and 3D versions, both based on the
  shallow water equations. Normally the 2D version
  is used.
• All databases, except for the wind forcing, are
  internal to the PCTides system.
• (All quotations in this section are taken from
  the web site listed above, unless otherwise
  noted.)

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Physics

• PCTides includes 2 tide/surge models the Global
  Environmental Modeling Services (GEMS) Coastal
  Ocean Model (GCOM2D and GCOM3D).
• GCOM2D is a depth-integrated, barotropic
  hydrodynamic model. It solves for SSH and mean
  current structure (i.e. no vertical variation).
• GCOM3D allows for vertical variations in the
  currents. It can be run in either barotropic mode
  (no thermal or density variation), or baroclinic
  mode (solves for temperature and salinity). The
  baroclinic mode is not generally available, and
  will not be discussed here.
• A wetting and drying algorithm for simulation of
  coastal flooding is included.

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Domain

• Selected by the user, using a rubber-banding
  method through the GUI or by entering
  latitude/longitude limits.
• Domains may be nested within one another to
  achieve higher spatial resolution in the inner
  domain.

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Grid and Coordinate System

• The version most commonly used by Navy METOC is
  2D, so has no vertical coordinate.
• The 3D version uses a z-coordinate system in the
  vertical.
• A Cartesian grid is used in the horizontal plane,
  with C type finite differencing.
• Grid arrays are constructed such that there are
  no more than 40,000 grid points (e.g. 200 x 200).
  This keeps simulations fast, while still allowing
  for large enough regions with fine enough
  resolution.

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Spatial Resolution

• Selected by the user through the GUI
• Generally from 1 to 10 km
• Bathymetry and open boundary conditions are
  automatically interpolated to the domain and grid
  selected by the user.

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Temporal resolution

• To optimize efficiency, different time steps are
  used to solve different aspects of the equations.
• The continuity equation and gravity wave and
  Coriolis terms use the shortest time step.
• The nonlinear advection terms use an intermediate
  time step.
• The surface and bottom stress terms are solved
  using the longest time step.

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Bathymetry

• 2' global bathymetry developed by NRL from the
  following bathymetry data bases
• This bathymetry provides an improved coastline
  and improved matching of bathymetry data near the
  coastline.

Database Spatial resolution
ETOPO5 5'
DBDBV 5' / 2' / 1' / 0.5 '
DAMEE (North Atlantic) 2.5 '
Gulf of Mexico 0.01
CHOI (Yellow Sea) 1.0 '
GTOPO2 (Sandwell) 2.0 '
IBCAO (Arctic) 2.5 km
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Boundary Conditions

• Included in PCTides are the Finite Element
  Solutions 95.1/2.1 (Shum et al. 1997) from the
  Grenoble global tide model (the same as those
  used for ADCIRC). These are used to provide sea
  surface displacements at the open boundaries of
  the ocean model.
• The same 8 tidal constituents as used for ADCIRC
  are used for PCTides.
• Atmospheric barometric displacement (change in
  sea level due to atmospheric pressure) is also
  specified at the open boundaries.

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User must make sure there is global tidal data
along all the open boundaries of the chosen
domain.
Grenoble Model M2 Tide Amplitude and Phase

• White areas indicate where there are no tidal
  solutions from global tidal model

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Forcing

• The model may be driven by astronomical tidal
  forcing (through the open boundaries) and / or
  surface winds and pressures.
• Winds and pressures may be entered manually (in
  which case they are uniform over the domain), or
  obtained from NOGAPS, COAMPSTM, or DAMPS through
  MetCast.

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Initialization

• All velocities are set to zero initially.
• The initial elevation field is obtained by
  interpolating the FES 95.1/2.1 elevation field to
  the model grid.
• It is customary to allow about 12 hrs for spin-up
  of the model. This allows spurious waves and
  boundary forcing to propagate out of the
  computational domain.
• The program is set up to automatically start the
  simulation 12 hrs before the user-chosen start
  time (or the start of the wind file if one is
  being used).
• With wind forcing, a longer spin-up time ( 24
  hrs) is used.

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Data Assimilation

• Sea level variations from measurements made at
  the 4500 International Hydrographic Office tidal
  stations are included in a PCTides database, and
  are used to constrain the solutions by using a
  weighted nudging approach described in Hubbert et
  al. 2001 (Blain et al. 2002).

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Implementation

• Can be run on PCs and UNIX systems.
• The average PCTides 48 hour forecast takes
  anywhere from 3 to 10 minutes of run time on a
  500 MHz PC. (Blain et al. 2002)

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The PCTides System
NRL combined Bathymetry
Winds/pressures from NOGAPS, COAMPS, DAMPS
IHO Coastal Tide Station Data
Boundary Conditions FES95.1/.2
2-D Ocean Model (Barotropic)
Tidal Heights and Barotropic Ocean Currents
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Output

• Results may be output in graphical or text
  format.
• Time series, with a time step typically of 10-12
  min, of sea level and currents are output at
  user-specified station locations.
• Spatial fields of velocity and sea level are
  output at a user-specified time interval (the
  minimum interval is 30 min).
• The length of the forecast is determined by the
  user, or the length of the wind forecast if one
  is being used.
• The sea level deviations output must be added to
  a specified reference level (such as mean sea
  level) to get actual water depths.

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Adapted from Harding et al.s 2001 GRC poster
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Reliability

• Both ADCIRC and PCTides generally produce sea
  level predictions that are within 10 cm and 30
  minutes of observed values.
• There are some areas of the world, such as off
  the U.S. West Coast, where results may be worse
  than quoted above due to reduced accuracy of the
  boundary conditions from the global tidal model.
• The following images are from the PCTides OPTEST.

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Chesapeake Bay Region4.4 km resolution
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Chesapeake Stationdepth 8 m
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PCTides Evaluation in the Yellow Sea
PCTides currents were evaluated against observed
currents from 4 bottom-mounted current profilers
from Sept. 1-30,1995 Current data were
not assimilated into the model.
Courtesy of Ruth Preller
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PCTides versus measured currents Sept. 25-30, 1995
Courtesy of Ruth Preller
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References

• Blaine, C.A., R.H. Preller, and A.P. Rivera,
  Tidal prediction using the Advanced Circulation
  Model (ADCIRC) and a relocatable PC-based system,
  Oceanography, 15 (1), 77-87, 2002.
• Hubbert, G.D., R.H. Preller, P.G. Posey, and S.N.
  Carroll, Software design description for the
  globally relocateable Navy time/atmosphere
  modeling system (PCTides), pp. 97, Naval Research
  Laboratory, Stennis Space Center, MS, 2001.
• Preller, R.H., P.G. Posey, G.D. Hubbert, S.N.
  Carroll, and L. Orsi, User's manual for the
  globally relocatable Navy tide/atmosphere
  modeling system (PCTides), pp. 68, Naval Research
  Laboratory, Stennis Space Center, MS, 2001.
• Preller, R, P. Posey, G. Dawson, K. Miles, M.
  Escarra, J. Ganong (2002) http//www7320.nrlssc.na
  vy.mil/pctides/

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Exercise

• Get tidal height prediction for the same location
  using ADCIRC, PCTides, and GFMPL. Go to
  http//www.oc.nps.navy.mil/nom/PCTides/