progress on the modification of offshore boundary conditions for full-bay roms simulations have...
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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.
Providence: sea level
Newport: sea level
East PassageChannel: currents
Blue: “large-domain” modelRed: “fullbay” model
Large-domain model open boundary forcing:•Tides from ADCIRC.•T, S from seasonal climatology.
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).
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.
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
Remaining Questions/Next Steps
• Big unanswered question: Why are model pressure gradient fluctuations in Bay so severely underestimated?1. Open boundary forcing still not right?2. Bottom drag coefficient in model needs adjustment?3. Wind stress too weak?
• Next Steps:1. 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.
2. Run existing models with changes to drag coefficient and/or increased wind stress. Should provide useful insight.
3. Create new large-domain model to simulate shelf circulation and sea level setup in vicinity of Bay mouth. Use this to force fullbay model.