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Progress on the Modification of Offshore Boundary Conditions for Full-Bay ROMS Simulations

Progress on the Modification of Offshore Boundary Conditions for Full-Bay ROMS Simulations. Have shown previously that ROMS simulations capture tides well, but that subtidal variability is not well simulated.

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Progress on the Modification of Offshore Boundary Conditions for Full-Bay ROMS Simulations

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  1. Progress on the Modification of Offshore Boundary Conditions for Full-Bay ROMS Simulations • Have shown previously that ROMS simulations capture tides well, but that subtidal variability is not well simulated. • Hypothesis in CHRP-II proposal: Poor subtidal model skill results from the fact that the shelf dynamics in the model is poorly simulated. • Proposed to extend “large-domain” model farther out on the continental shelf and to force this model with output of regional models. • Before building a new model, have examined the model and observations with an eye towards a better understanding of the dynamics.

  2. Providence: sea level Blue: “large-domain” model Red: “fullbay” model East Passage Channel: currents Newport: sea level • Large-domain model open boundary forcing: • Tides from ADCIRC. • T, S from seasonal climatology.

  3. North/South Velocity (EP Channel) North South North South

  4. Depth-Averaged North/South Velocity (EP Channel) Model skill (Wilmott) = 0.75

  5. Approximate depth-averaged momentum balance (north/south direction) A B C D E A. Local acceleration (time change of velocity): estimate from ADCP obs. (E. Passage channel). B. Barotropic pressure gradient (due to surface slope): estimate from sea level obs. (Prov. and Newport). C. Baroclinic pressure gradient (due to density gradient): estimate by difference. D. Wind stress ( ): estimate from wind obs. (Quonset). E. Bottom stress ( ): estimate from ADCP obs. (near-bottom bin).

  6. Depth-Averaged Momentum Balance (EP channel) Up-estuary Down-estuary

  7. Depth-Averaged Momentum Balance (EP channel) Up-estuary Down-estuary

  8. Momentum Balance Obs. vs Model

  9. Forcing from FVCOM model Model results for 2006 obtained from C. Chen, UMASS Dartmouth (for OSAMP project). Model output sampled along large-domain model open boundary and used as forcing.

  10. Force Large-Domain Model: • Low-pass filtered sea level and velocity from FVCOM simulation applied along open boundaries of large-domain model (in addition to tides and T/S climatology as in standard run). Open boundaries

  11. Momentum Balance Obs. vs Models

  12. Sea Level, Obs. vs Models

  13. Remaining Questions/Next Steps • Big unanswered question: Why are model pressure gradient fluctuations in Bay so severely underestimated? • Open boundary forcing still not right? • Bottom drag coefficient in model needs adjustment? • Wind stress too weak? • Next Steps: • Obtain updated version of Chen model. Check its fidelity with Newport sea level compared to present version. If improved, then extract forcing from it and re-run large-domain and fullbay models. • Run existing models with changes to drag coefficient and/or increased wind stress. Should provide useful insight. • Create new large-domain model to simulate shelf circulation and sea level setup in vicinity of Bay mouth. Use this to force fullbay model.

  14. Sea Level and Wind

  15. Sea level/wind correlations

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