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Version 2 ROMS Model for Computation of GEMBOX Exchanges

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).

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Version 2 ROMS Model for Computation of GEMBOX Exchanges

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  1. 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.

  2. Blue: “large-domain” model Red: “fullbay” model • 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. New Rivers Open boundaries

  3. Subtidal Sea Level, Velocity Sea Level: Providence Sea Level: Newport Blue: observations Black: model v1 Red: model v2 Sea Level Difference Velocity: E. Passage Channel

  4. Model/Obs. Comparison, Greenwich Bay Version 1 Version 2

  5. Model Skill, Salinity at DEM Stations Surface Bottom Version 1a: large-domain model forced with FVCOM results. spatially variable wind forcing.

  6. 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.

  7. Element Flushing Times: Salt or Freshwater • Dye fluxes represent gross (one-way) advective plus • diffusive 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 < 0 or for j where flux_salti,j > 0

  8. V2 Model: Time Evolution of Flushing Time

  9. Version 2 Model: Median Flushing Times Upper Layer Elements Lower Layer Elements

  10. What Causes Variability of Flushing Time? • Seems to be complex interplay of factors. • e.g. river discharge and northward wind: Box 2, surface Box 2, bottom southward northward southward northward

  11. 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: • ROMS model description/skill assessment. • Flushing time and its variability.

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