#### Transcript Progress on modifying offshore boundary conditions for full

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 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. North/South Velocity (EP Channel) North South North South Depth-Averaged North/South Velocity (EP Channel) Model skill (Wilmott) = 0.75 Approximate depth-averaged momentum balance (north/south direction) A B ¶v ¶h g ¶ = -g ò ¶t ¶y H ¶y -H 0 C D E bottom æ r - r0 ö t ty ò çè r ÷ødzdz + H - H 0 z 0 wind y 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 ( t ywind = CD windy windy): estimate from wind obs. (Quonset). E. Bottom stress ( t ybottom = CD v bottom vbottom ): estimate from ADCP obs. (near-bottom bin). Depth-Averaged Momentum Balance (EP channel) Up-estuary Down-estuary Depth-Averaged Momentum Balance (EP channel) Up-estuary Down-estuary Momentum Balance Obs. vs Model 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 Momentum Balance Obs. vs Models Sea Level, Obs. vs Models 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. Sea Level and Wind Sea level/wind correlations