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Primitive equation models These are the most sophisticated type of ocean circulation model, including more of the physics than the analysis systems and shallow water equation models we have discussed previously. While their increased complexity makes them applicable to a broader class of applications, and should result in more accurate solutions, it can also be more difficult to diagnose their behavior and to understand how various model choices affect the results.
Fixed Vertical Coordinates • POM • SWAFS • POP • NCOM Lagrangian Vertical Coordinate • NLOM Hybrid Vertical Coordinate • HYCOM
POM Princeton Ocean Model The first set of models we will examine are based on the Princeton Ocean Model, which was developed in the late 1970 s by Blumberg and Mellor (of Princeton University), with subsequent contributions by other people. It is a very widely used model, both for research and operationally.
POM http: //www. aos. princeton. edu/WWWPUBLIC/htdocs. pom/ POM is a sigma coordinate, free surface, primitive equation ocean model, which includes a turbulence sub-model. The model has been used for modeling of estuaries, coastal regions and open oceans.
Physics • It contains an imbedded second moment turbulence closure sub-model to provide vertical mixing coefficients. The turbulence model does a reasonable job simulating mixed layer dynamics, although there have been indications that calculated mixed layer depths are a bit too shallow (Mellor, 1998). • Complete thermodynamics have been implemented. (Mellor, 1998) • The model has a free surface.
Grid and Coordinate System • It is a coordinate model (vertical coordinate is scaled on the water column depth). The coordinate system is probably a necessary attribute in dealing with significant topographical variability such as that encountered in estuaries or over continental shelf breaks and slopes. Together with the turbulence submodel, the model produces realistic bottom boundary layers. (Mellor, 1998) • Significant errors in the pressure gradient terms can result when sigma coordinate models with insufficient horizontal resolution are used with very steep topography. • The horizontal grid uses curvilinear orthogonal coordinates and an "Arakawa C" differencing scheme. (Mellor, 1998)
Time Step • The model has a free surface and a split time step. The external mode portion of the model is 2 D and uses a short time step based on the CFL condition and the external wave speed. The internal mode is three-dimensional and uses a long time step based on the CFL condition and the internal wave speed. (Mellor, 1998) • The calculation of the 3 D (internal) variables is separated into a vertical diffusion time step and an advection plus horizontal diffusion time step. The former is implicit (to accommodate small vertical spacing near the surface and bottom) whereas the latter is explicit. (Mellor, 1998)
Boundary Conditions • A number of different conditions may be implemented along the open boundaries for the external mode. – Sea surface elevation – Depth-integrated flow – Radiation conditions • There also numerous options for the open boundary conditions on the internal mode. – Radiation conditions – Advection of T and S – Specified inflow
Forcing • • Wind stress Heat flux River inflow Tides
Output • 3 D fields of velocity, T, and S • SSH
References http: //www. aos. princeton. edu/WWWPUBLIC/ht docs. pom/ Mellor, G. L. , Users Guide for a Three. Dimensional, Primitive Equation, Numerical Ocean Model, Program in Atmospheric and Oceanic Sciences, Princeton University, Princeton, NJ, 1998.
MODAS/POM MODAS Relocatable POM Model Primary contacts: Dan Fox (NRLSSC); Martin Booda (NAVO); Germana Peggion (USM) A relocatable version of the Princeton Ocean Model which takes advantage of MODAS for model initialization and data assimilation has been developed at NRLSSC. This model has been run operationally for a number of domains. It is likely that in the future, NCOM rather than POM, will be used for this purpose.
MODAS/POM http: //www 7320. nrlssc. navy. mil/modas/pom. html • Provide short-term (2 -day) forecast • User-friendly interface • Relocatable from deep to shallow, from open sea to inlets • Portability (toward PC) • Primary clients: NAVO and Navy operational units Courtesy of Germana Peggion
Domain • Fine resolution domains may be nested inside coarser resolution domains. • Domains in recent use include: Yellow Sea, Arabian Gulf, Southeastern US, Strait of Gibraltar, Taiwan Strait • Establishment of new domains requires care in picking boundary locations and specifying other parameters. • The number of domains in use is being reduced over time with the expectation that a new relocatable POM version, and eventually NCOM, will be used in the future.
Spatial Resolution • User specifies the resolution in MODAS • Current domains have resolution anywhere from 0. 5 km to over 20 km • Default configuration has 25 levels in the vertical • User may specify up to 100 levels, and how they are distributed in the water column (as a percentage of depth).
Initialization This version of POM can be initialized in various ways using the information from the MODAS analysis. • Cold start: MODAS T and S grids, but not geostrophic currents, are used. • Diagnostic mode: POM is run for 1 -2 days, holding initial MODAS T and S fields constant so the dynamic model develops its own currents consistent with the user-supplied density field. • Warm start: MODAS-estimated geostrophic currents (default), or currents extracted from a larger domain numerical ocean model, are used. (Fox et al. 2002 a)
• Presently, all but one POM domains running at NAVO use the North Pacific Ocean Nowcast/Forecast System for initialization. • The area around Cadiz, Spain uses the daily MODAS analysis for initialization.
An example of regional finer resolution POM models initialized from a coarser resolution basin scale POM, North Pacific Nowcast/Forecast follows. NPACNFS consists of a data assimilative dynamic ocean model based on POM, with 1/4 o horizontal resolution and 26 sigma levels in the vertical, the MODAS 3 D ocean temperature/salinity analysis, and a real-time data stream from NRL/NAVO satellite data fusion center and NOGAPS from FNMOC.
The North Pacific Ocean Nowcast/Forecast System (NPACNFS) is an automated real-time ocean prediction system for the North Pacific Ocean. It produces daily nowcast/forecast sea level variation, 3 D current, temperature and salinity for the North Pacific Ocean.
Buoy Gauge 26 km From Harding et al. ’s 2001 GRC poster 6 km 1. 5 km
Boundary Conditions • Radiation-like open boundary condition requiring reference velocities. • Reference velocity values are held constant during the forecast. • MODAS T and S are used to calculate baroclinic geostrophic reference velocity. • Barotropic reference velocity (transport) is derived from MODAS or a numerical ocean model. • Tidal heights (the same solutions from the Grenoble tidal model as are used in PCTides and ADCIRC) applied at open boundaries every baroclinic mode time step (Fox et al. 2002 a)
Forcing • NOGAPS or COAMPSTM winds • Tidal forcing may be included as a boundary condition. Product Info should indicate whether or not tidal forcing has been included.
Location: Strait of Gibralter Type: Princeton Ocean Model Description: Currents Surface Series (U) POC: NAVO - Princeton Ocean Model Library Custodian COMM: 228 -688 -5176 DSN: 828 -5176 or E-mail Us Update Cycle: 24 hour(s) Typical File Size: 35(K) Level-of-Confidence: This product is unvalidated and fully beyond the control of NMOC to ensure the quality of the underlying data and/or availability of product. Current File Statistics: i. cadvelpom 000_0000. gif Size: 48 (Kbytes) Last Update: 19 -Jul-12: 50 CDT (U) ii. cadvelpom 024_0000. gif Size: 51 (Kbytes) Last Update: 19 -Jul-12: 50 CDT (U) iii. cadvelpom 048_0000. gif Size: 56 (Kbytes) Last Update: 19 -Jul-12: 50 CDT (U) Additional Information: i. Product reflects geostrophic influence on model. (U) ii. Product reflects wind-driven influence on model. (U) iii. Product reflects tidal influence on model. (U) iv. Product does NOT reflect Sea Surface Height influence on model. (U) Location: Taiwan Strait Type: Princeton Ocean Model Description: Currents over Temperature Surface Series (U) POC: NAVO - Princeton Ocean Model Library Custodian COMM: 228 -688 -5176 DSN: 828 -5176 or E-mail Us Update Cycle: 24 hour(s) Typical File Size: 73(K) Level-of-Confidence: This product is unvalidated and fully beyond the control of NMOC to ensure the quality of the underlying data and/or availability of product. Current File Statistics: i. taivelsstpom 024_0000. gif Size: 99 (Kbytes) Last Update: 19 -Jul-13: 06 CDT (U) ii. taivelsstpom 048_0000. gif Size: 95 (Kbytes) Last Update: 19 -Jul-13: 06 CDT (U) Additional Information: i. Product reflects geostrophic influence on model. (U) ii. Product reflects wind-driven influence on model. (U) iii. Product does NOT reflect tidal influence on model. (U)
Data Assimilation • Data assimilation is through MODAS, so in areas where MODAS doesn’t use satellite SSH, that won’t be in relocatable POM either. • No new data is assimilated during the forecast.
Implementation • Relocatable POM is included in the full MODAS 2. 1 version (at NRLSSC) and MODAS-Heavy (at NAVO). Presently it is not implemented at any of the METOC regional centers.
Output • Nowcast, and 24 and 48 hr forecasts • Velocity, T, MLD, critical depth, deep and shallow sound channel axes, depth excess • Depths for which V and T are shown vary by domain • Graphical format • Animations (of the same 3 pictures as in series) available for some domains • No byte-encoded or wavelet compressed SV fields • Some fields for some domains output for REACTs (viewed with Arc. Explorer) Above is as of 7/19/02
Example Implementation • Updates once per day. • 24 and 48 h forecasts. • Currents, and currents over temperature, at surface and selected subsurface layers are displayed. • Critical depth, shallow sound channel axis, deep sound channel axis, depth excess, mixed layer depth, sonic layer depth, and sea surface temperature are output. • Products may be output in graphical, Arc. View (for REACTS), EOF-compacted, Net. CDF or other formats
Velocity scale arrow is same as in
Gulf of Cadiz
POM SST and Sfc. Currents Relative to Satellite SST Unclassified NAVOCEANO MCSST Arabian Gulf – Gulf of Oman NAVO IR Composite 24 Feb 98 Courtesy of John Harding, NRL-SSC
References http: //www 7320. nrlssc. navy. mil/modas/ Fox, D. N. , C. N. Barron, M. R. Carnes, M. Booda, G. Peggion, and J. Gurley, The Modular Ocean Data Assimilation System, Oceanography, 15 (1), 22 -28, 2002 a.