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Sensitivity Studies Using Nested HYCOM Models

Sensitivity Studies Using Nested HYCOM Models. Patrick Hogan Luis Zamudio Alan Wallcraft E.Joseph Metzger. Naval Research Laboratory Stennis Space Center, MS. 2004 Layered Ocean Model Users’ Workshop February 9-11, 2004 RSMAS, Miami, FL.

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Sensitivity Studies Using Nested HYCOM Models

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  1. Sensitivity Studies Using Nested HYCOM Models Patrick Hogan Luis Zamudio Alan Wallcraft E.Joseph Metzger Naval Research Laboratory Stennis Space Center, MS 2004 Layered Ocean Model Users’ Workshop February 9-11, 2004 RSMAS, Miami, FL

  2. HYCOM Coastal Nesting Strategy • Purpose • Provide accurate, generalized nesting capability to support • littoral applications for the next Navy global prediction system • (based on HYCOM, 2006 transition). • Evaluate the next generation coastal ocean models (HYCOM, • NCOM, perhaps others (ROMS?)). • Develop coastal modeling capabilities for HYCOM. • Model-model and model data inter-comparisons • Approach • Determine the sensitivity to nesting techniques and parameters, the • impact of nesting with like and unlike model design and/or • vertical distribution. • Examine the impact of nesting on ocean dynamics with emphasis • on the accurate propagation of oceanic features from different • dynamical regimes across nested model boundaries. • Implement and evaluate coastal/littoral HYCOM Encl (7)

  3. Initial approach: First, nest coastal HYCOM and NCOM within basin-scale HYCOM at the same horizontal resolution • Provides a benchmark for model-model comparisons • Evaluate sensitivity to vertical remapping methods • Evaluate methods for lateral transmission of information • Accuracy of representation of coastal dynamical processes • Propagation of deep water events into the coastal region Some preliminary results HYCOM to HYCOM, same vertical structure • Gulf of California HYCOM to NCOM-like, 26-layer Hybrid to 40-level sigma-z • Gulf of Mexico

  4. Sensitivity Studies for HYCOM to HYCOM Nesting • The Gulf of California a good test bed for coastally trapped waves • Can be generated by Hurricane or El Niño • Larger GoC used to examine impact of waves generated inside domain (Metzger) • Smaller GoC will be used to examine impact of boundary condition • on externally generated waves Current status of nesting in HYCOM Relaxation (nudging) within a sponge zone for the baroclinic mode Method of Characteristics for the barotropic mode “off-line”, boundary information comes from archive files Don’t need to know nested area in advance, but updating frequency limited by archive file frequency

  5. Gulf of California Nesting Sensitivity Studies (all models have 8 km resolution) 8 km Pacific HYCOM provides boundary Conditions to Gulf of California HYCOM 27th 24th Hurricane generated within domain • The updating frequency (both modes) • The e-folding time across the buffer zone • The width of the buffer zone • Exclude the baroclinic/barotropic mode • Which variables are updated Hurricane signal must pass through boundary

  6. The smaller Gulf of California domain must accurately pass the coastal- trapped waves and eddies across the nested boundary Historical HYCOM nesting parameters: Method of characteristics for Barotropic mode (u,v,p) 1-day updating frequency Relaxation to outer grid solution in Buffer zone for baroclinic mode 10 gridpoint wide relaxation zone 1-10 day relaxation e-folding time 6-day updating frequency Open boundaries • 20-layers • Non-assimilative • Forced with NOGAPS

  7. Standard Nesting Parameters Same geometry Same horz. res. Same vert. res. RMS error map (wrt Pacific model over GoC domain) Time series of domain- wide RMS error Different variables respond differently

  8. E-folding time in BZ 1-10, 1-5, .1-1, .1-.5, .1-.2 10 gridpoints 3 hours Barotropic + baroclinic Sensitivity to: Updating frequency 3 hours, 1,2,4,6 days 10 gridpoints 0.1-1.0 e-folding Barotropic + baroclinic

  9. Sensitivity to: Barotropic/baroclinic mode Width of buffer zone Barotropic or baroclinic only 1,2,3,4,5,10 gridpoints 10 gridpoints 0.1-1.0 e-folding 3 hourly 3 hourly 0.1-1.0 e-folding Barotropic + baroclinic

  10. Lowest Error Nesting Parameters Matzalan * Hurricane Julliette forms (outside of boundary) Hurricane Jullitte passes through boundary RMS error map 1-10 gridpoints .1-1 day e-folding 3 hour updating Baroclinic+barotropic Time series of domain-wide RMS error

  11. SSH Anomaly vs. Matzalan Tide Guage Station E-folding time Updating frequency Width of buffer zone Barotropic/Baroclinic

  12. ~8 km (1/12°) Atlantic HYCOM Mississippi Bight nest Florida Current nest Portugal nest Gulf of Mexico IAS nest Non-assimilative; forced with NOGAPS

  13. Nested Gulf of Mexico 8 km to 8 km SSH snapshot from ATL model used to restart and and provide boundary conditions to GoM model ATL model has 20 m coastline Nested Gulf of Mexico SSH 1-day after restart from ATL GoM has 5 m coastline with 10 m minimum depth 10 gridpoint buffer zone 1-10 day e-folding 1 day updating for Barotropic and baroclinic

  14. Nested Gulf of Mexico 8 km to 8 km Snapshot of SSH from 8 km ATL model 4 months later Snapshot of SSH from 8 km Gulf of Mexico model • Boundary conditions • Coastline change

  15. 26-layer hybrid vs. 40-level sigma-z (“HYCOM in NCOM mode”) True NCOM – full cell topography HYCOM/NCOM –partial cells 8 km 26-layer hybrid GoM model 1 month after restart from 8 km ATL model 8 km 40-level sigma-z GoM model restarted from 26 layer hybrid GoM model (1 month of adjustment to new coastline allowed for) 1 day after restart • Vertical remapping via PLM • Smooth adjustment to different • vertical descritization

  16. 8 km 26-layer Hybrid GoM Both 3 months after restart from “adjusted” nested GoM model 8 km 40-level sigma-z GoM • Similar solutions after 3 months • despite different vertical discritization

  17. Zonal cross-section (26.9N) of Salinity on December 1, 1999 (4 mo.) 1000 40-level sigma-z Vertical coordinate overlaid Salinity contours overlaid Shelf-break front 1000 26-layer hybrid

  18. Near Future Plans Determine the optimal vertical configuration (?) What is the impact of possibly retaining isopycnals over the shelf? What is the impact of full-cell topography in NCOM’s z-level mode? What is the impact due to the location of the open boundary? • Several test cases: • Different dynamical regimes • HYCOM to HYCOM (different horizontal/vertical resolution, etc.) • NCOM to NCOM, ROMS(?) (coupling different model designs) • HYCOM to HYCOM with fixed vertical coordinates over the shelf • HYCOM to NCOM (using HYCOM) with full/partial-cell topography • In general, Anything to Anything Add coastal capabilities to HYCOM • Realistic River plume dynamics • Tidal forcing • Realistic bottom boundary layer • Treatment of the free surface

  19. THE END

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