DTIC ADA480644: Global Ocean Nowcasts and Forecasts with the Navy Coastal Model (NCOM)

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by  Defense Technical Information Center

to directly verify predictions such as those of Fig. 2. quired information regarding the surrounding envi-
Such efforts will require an interdisciplinary ap- ronment to localized models more specialized for a
proach, involving NRL researchers with expertise in particular task or domain. In general, nested models
a variety of areas: design of acoustic experiments, will have more detailed forcing, topography, addi-
scattering theory, materials science, laser profil- tional data for assimilation, or higher resolution nec-
ometry, ground-truth geoacoustic measurements, essary for improved local detail. The global model in-
and the operation of NRL tank facilities with com- cludes inflow from almost 1000 rivers to improve the
puter-controlled sources and receivers. fidelity of coastal salinity. Global NCOM is designed
[Sponsored by ONR] to be suitable for inclusion in a coupled ocean-atmo-
sphere modeling system, and it is also designated as
RRRRReeeeefffffeeeeerrrrreeeeennnnnccccceeeeesssss the host for an embedded ice model, PIPS3, which is
1R.F. Gragg, D. Wurmser, and R.C. Gauss, “Small-slope Scattering
in development for transition.
from Rough Elastic Ocean Floors: General Theory and
Computational Algorithm,” J. Acoust. Soc Am. 111111111100000, 2878-2901
(2001). IIIIImmmmmpppppllllleeeeemmmmmeeeeennnnntttttaaaaatttttiiiiiooooonnnnn::::: NCOM is a free-surface, primi-
2R.J. Soukup and R.F. Gragg, “Scattering from a Rocky Bottom at tive-equation model based primarily on two other
2-3.5 kHz: Measurements and Modeling,” J. Acoust. Soc Am. (to
appear). (cid:1)(cid:1)(cid:1)(cid:1)(cid:1) models, the Princeton Ocean Model and the Sigma/
Z-level Model.2 In its global configuration, we have
implemented NCOM on a curvilinear horizontal
grid designed to maintain a grid-cell horizontal as-
Global Ocean Nowcasts and pect ratio near 1. Horizontal resolution varies from
19.5 km near the equator to 8 km or finer in the Arc-
Forecasts with the Navy Coastal
tic, with midlatitude resolution of about 1/8∞ lati-
Ocean Model (NCOM)
tude (~14 km). Figure 4 shows a sea surface tempera-
ture (SST) snapshot from the full domain in a projec-
C.N. Barron, R.C. Rhodes, L.F. Smedstad, tion that shows the actual distribution in the logical
C.D. Rowley, and P. J. Martin domain. Horizontal resolution has been sacrificed to
Oceanography Division allow increased vertical resolution. To improve the
A.B. Kara detail of upper-ocean dynamics, we maintain a maxi-
Florida State University mum 1-m upper level thickness in a hybrid sigma/z
vertical configuration with 19 terrain-following
IIIIInnnnntttttrrrrroooooddddduuuuuccccctttttiiiiiooooonnnnn::::: The global ocean is a seamless sigma-levels in the upper 137 m over 21 fixed-thick-
body where open-ocean systems shape and are ness z-levels extending to a maximum depth of 5500
shaped by nearshore conditions, surface processes m. Model depth and coastline are based on a global
drive and respond to interior circulation, and local- 2-minute bathymetry produced at the Naval Re-
ized events often can be predicted and understood search Laboratory (NRL).
only within a larger context. To support Navy opera- The present daily model run consists of a 72-
tions and other research and operational activities hour hindcast to assimilate fields that include recent
within such an environment, we have developed and observations, and a 72-hour forecast. Longer fore-
are transitioning to the Naval Oceanographic Office casts are being evaluated. Global NCOM uses atmo-
(NAVO) a fully global implementation of the Navy spheric forcing from the Navy Operational Global
Coastal Ocean Model (NCOM). We have endeav- Atmospheric Prediction System, with latent and sen-
ored to produce a friendly environment for nesting sible heat fluxes calculated internally using NCOM
higher resolution models wherever the need should SST. Tidal heights and currents can be added using a
arise. Some global NCOM data products of particu- separate user-specified model, with validation and
lar interest include surface currents and tempera- boundary condition experiments focusing on using
ture, mixed-layer depth, current and thermohaline the NAVO operational model PC Tides.
profiles, and shelf circulation.
Global NCOM extends present global Navy op- AAAAAssssssssssiiiiimmmmmiiiiilllllaaaaatttttiiiiiooooonnnnn: Data assimilation is based on glo-
erational model capabilities1 into the Arctic and to bal profiles of temperature and salinity derived us-
nearshore regions, with a minimum depth of 5 m. ing operational sea-surface fields and in situ data
Operational roles of global NCOM include providing within the Modular Ocean Data Assimilation Sys-
standalone data where global resolution is sufficient tem (MODAS)3. The operational global 1/16∞ Navy
and timely overviews of local circulation as detailed Layered Ocean Model (NLOM), while limited to
localized products are prepared. Perhaps its most im- subpolar waters deeper than 200 m, has higher hori-
portant purpose is to provide boundary conditions zontal resolution than Global NCOM and is better
used by regional or relocatable models, giving re- suited to directly assimilate altimeter data and fore-
ocean science and technology 2003 NRL Review 175
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1. REPORT DATE 3. DATES COVERED
2003 2. REPORT TYPE 00-00-2003 to 00-00-2003
4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER
Global Ocean Nowcasts and Forecasts with the Navy Coastal Model
5b. GRANT NUMBER
(NCOM)
5c. PROGRAM ELEMENT NUMBER
6. AUTHOR(S) 5d. PROJECT NUMBER
5e. TASK NUMBER
5f. WORK UNIT NUMBER
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION
Naval Research Laboratory,Oceanography Division,1002 Balch REPORT NUMBER
Boulevard,Stennis Space Center,MS,39522-5001
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11. SPONSOR/MONITOR’S REPORT
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FIGURE 4
The global Navy Coastal Ocean Model (NCOM) extends from the Arctic Ocean to the coast of Antarctica and from the open ocean
over the shelf break to nearshore regions. Plots of model products such as this sea surface temperature field are available from
www.ocean.nrlssc.navy.mil/global_ncom. A variety of global NCOM validation tests continue. For example, the histograms summa-
rize comparisons with 219 unassimilated, year-long buoy SST time series in the Equatorial Pacific, North Pacific, and shelf regions of
the United States. One of these cases (line plot) shows NCOM agreement (blue) with one TAO buoy (black) during the extreme 1998
El Niño to La Niña transition.
176 2003 NRL Review ocean science and technology
cast the location of fronts and eddies. To take advan- parisons with drifter trajectories and ADCP sec-
tage of this capability, NLOM sea surface height tions. Finally, event comparisons in regions of inter-
(SSH) fields are paired with MODAS2D SST to de- est may be made using a variety of observational
rive temperature and salinity profiles using the sources, such as the comparison shown in Fig. 6 of
MODAS dynamic climatology. NCOM relaxes to- ocean color products compared with NCOM sur-
ward these profiles according to a spatially variable face height and currents in the Arabian Sea.
weighting function. Figure 5 shows four year-long
time series that demonstrate the progression from PPPPPlllllaaaaannnnnsssss: We are transitioning global NCOM to
background climatology, to assimilation field, to NAVO, with delivery for operational testing sched-
model result, with the unassimilated observations uled for February 2003. Testing continues on modi-
for comparison. fied assimilation schemes, boundary condition ex-
traction, and mixed-layer tuning. Global NCOM
VVVVVaaaaallllliiiiidddddaaaaatttttiiiiiooooonnnnn: Validation of global NCOM against data provide boundary information for a number of
observation-based standards uses a variety of experi- ongoing research efforts.
ments and criteria. Some are climatological compari-
sons against historical means, including evaluation AAAAAccccckkkkknnnnnooooowwwwwllllleeeeedddddgggggmmmmmeeeeennnnntttttsssss: The authors thank Dr. H.
of mean eddy kinetic energy at various depths and Hurlburt (NRL) and Dr. W. Schmitz (WHOI emeri-
transport and velocity distributions through straits tus) for their advice and guidance during develop-
or other sections. NCOM nowcasts and forecasts are ment and transition of the Global NCOM system;
compared with satellite observations, prior to as- Dr. A. Wallcraft (NRL) for his work in making
similation, or with independent in situ data, as NCOM code portable and scaleable; Dr. D. Ko for
shown in Fig. 4. In situ data are also used to evaluate his work on the global bathymetry and model grid;
subsurface temperatures and mixed layer depth (Fig. and Dr. R. Arnone (NRL) and Dr. J. Kindle (NRL) for
5). Validations of ocean currents are based on com- help in the comparison with ocean color. We also
FIGURE 5
Time-series from 2001 at a TAO buoy
location in the equatorial Pacific (8∞S,
155∞W). The bottom series indicates
the MODAS climatological back-
ground. Using real-time MODAS SST
and NLOM SSH, the MODAS
dynamic climatology produces a field
that is assimilated into global NCOM.
The ability of global NCOM to
resolve the mixed-layer dynamics
allows it to produce a mixed-layer
depth (black line on each series) in
closer agreement with the variability
measured in the observations.
ocean science and technology 2003 NRL Review 177
48°E 52°E 56°E 60°E 64°E 68°E 72°E
MODIS composite
24°N 30 Sep — 7 Oct 2002
Diffuse Attenuation
Coefficient at 532 nm
20°N
52°E 56°E 60°E 64°E
16°N
12°N
8°N
Cyclonic
0.01 0.03 0.08 0.2 0.7 2 Eddies
Global NCOM 3 Oct 2002
Surface Currents over Height (cm)
24°N 40
22°N 30
Cyclonic Anticyclonic
Eddies Eddies
20°N 20
18°N 10
16°N 0
52°E 56°E 60°E 64°E
FIGURE 6
Global NCOM SSH and surface currents in the Arabian Sea are compared with a MODIS composite produced by the Ocean
Optics section at NRL (Ocean Color at http://www7300.nrlssc.navy.mil/products.html). Eddies located in the global NCOM
analysis agree with observed features delineated by gradients in diffuse attenuation coefficient.
thank Ms. J. Dastugue for her assistance in develop- The Influence of Microbial Fe(III)
ing the Global NCOM web site at Reduction on Clayey Sediment
www.ocean.nrlssc.navy.mil/global_ncom. This work Flocculation
is made possible through the support of Space and
Naval Warfare Systems Command PMW155 and
J.-W. Kim, Y. Furukawa, T. Daulton, S.E. O’Reilly,
computational resources provided by the Depart-
and S. Newell
ment of Defense High Performance Computing
Marine Geosciences Division
Modernization Program.
[Sponsored by SPAWAR]
IIIIInnnnntttttrrrrroooooddddduuuuuccccctttttiiiiiooooonnnnn::::: Understanding the role of floccula-
tion of suspended sediments carried by rivers is im-
RRRRReeeeefffffeeeeerrrrreeeeennnnnccccceeeeesssss
1R.C. Rhodes et al., “Navy Real-time Global Modeling Systems,” portant to industries and naval undersea operations.
Oceanog. 1111155555, 29-43 (2002). This “fluid mud” can be responsible for the variability
2P.J. Martin, “Description of the Navy Coastal Ocean Model of littoral sediment properties such as turbidity, shear
Version 1.0,” NRL Report FR/7322-00-9962, 45 pp. (2000).
strength, and compressibility. Many theoretical and
3D.N. Fox, W.J. Teague, C.N. Barron, M.R. Carnes, and C.M. Lee,
laboratory studies have dealt with the physical chem-
“The Modular Ocean Data Analysis System (MODAS),” J. Atmos.
Ocean. Technol. 1111199999, 240-252 (2002). (cid:1)(cid:1)(cid:1)(cid:1)(cid:1) istry and fluid dynamics of interactions among sedi-
178 2003 NRL Review ocean science and technology