Version 2 ROMS Model for Computation of GEMBOX Exchanges

• Version 2 model changes: Open boundary forcing of large-domain model

taken from regional model (C. Chen’s FVCOM). Spatially variable wind forcing from high-resolution

atmospheric model (also from Chen). Two additional rivers (plus WWTF) entering western

end of Greenwich Bay.• Version 2 model skill improved in comparison to

Version 1.• Have generated version 2 model dye exchanges for

2006. 2007 run in progress.• Computing flushing times for GEMBOX elements.

Large-Domain Model Forcing Changes:•Low-pass filtered sea level, velocity, temperature, and salinity from FVCOM simulation applied along open boundaries of large-domain model (in addition to tides as in standard run).•Spatially variable wind.

Fullbay Model Forcing Changes:•Addition of river inflows in W. Greenwich Bay.•Spatially variable wind.•Bay mouth open boundary forcing from new version of large domain model.

Open boundaries

Blue: “large-domain” modelRed: “fullbay” model

New Rivers

Subtidal Sea Level, Velocity

Blue: observationsBlack: model v1Red: model v2

Sea Level: Providence

Sea Level: Newport

Sea Level Difference

Velocity: E. PassageChannel

Model/Obs. Comparison, Greenwich BayVersion 2Version 1

Model Skill, Salinity at DEM StationsSurface Bottom

Version 1a: large-domain model forced with FVCOM results. spatially variable wind forcing.

Utility of Dye Exchange Estimates (In Addition to Use for GEMBOX)

Hypothesis: Dye exchange fractions can reveal details of physical exchange of materials throughout N. Bay.

• Long time series of exchange fractions provides information on exchange under a wide range of forcing conditions.

• Can compute flushing times on a daily basis for individual box model elements (or groups of elements) using exchange fractions.

• Aim is to develop a statistical description of flushing and exchange processes.

Element Flushing Times: Salt or Freshwater•Dye fluxes represent gross (one-way) advective plusdiffusive transport.•Net salt flux between elements i and j expressed using dye fractions (similar for Freshwater (FW)):

Estimate flushing time from salt (FW) mass within an element and salt (FW) flux into or out of that element:

for j where flux_salti,j < 0or

for j where flux_salti,j > 0

V2 Model: Time Evolution of Flushing Time

Version 2 Model: Median Flushing TimesUpper Layer Elements Lower Layer Elements

What Causes Variability of Flushing Time?

Seems to be complex interplay of factors.e.g. river discharge and northward wind:

northward northwardsouthward southward

Box 2, surface Box 2, bottom

Next Steps• Finish dye exchange run for 2007 using version 2 model

(within next couple of weeks).

• Simulation of additional years: 2008, and possibly 2009?

Relatively straightforward to obtain forcing data. Simulations will thus be comparable to 2006-2007.

2014?Open boundary and wind forcing data may not be available from the same source. Can explore other options. Upshot may be that simulations will not be easily compared with 2006-2007 because of different model forcing.

• Papers: 1. ROMS model description/skill assessment.2. Flushing time and its variability.