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.

North/South Velocity (EP Channel)

North

South

South

North

Model skill (Wilmott) = 0.75

Depth-Averaged North/South Velocity (EP Channel)

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).

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