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Bridging the Gap between idealized and realistic numerical river plume simulations

Bridging the Gap between idealized and realistic numerical river plume simulations. Robert Hetland Texas A&M University. Feedback between idealized and realistic modeling. Numerical consistency. Metrics (Depends on user requirements). Idealized modeling. Realistic modeling.

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Bridging the Gap between idealized and realistic numerical river plume simulations

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  1. Bridging the Gap between idealized and realistic numerical river plume simulations Robert Hetland Texas A&M University

  2. Feedback between idealized and realistic modeling Numerical consistency Metrics (Depends on user requirements) Idealized modeling Realistic modeling Physical consistency

  3. Transition to operational models • What are the requirements of the model end-user? • A metric that embodies this requirement. • How do you quantify good model performance? • Skill assessment measures model’s ability to reproduce the desired metric.

  4. Metric - Fresh water flux • Broad, integrative metric for buoyancy flow as a whole. • Depends on definition of reference salinity. • Also interested in the nature of the fresh water flux (e.g., what kind of water carries the fresh water?)

  5. Model skill - ‘Synoptic skill’

  6. Anatomy of a river plume • Assume that the plume may be divided into dynamically distinct regions: • Near field where advection of momentum is important. • Far field where wind forcing and the earth’s rotation are the dominant physics.

  7. Dynamically definedplume regions - cross section

  8. Dynamically definedplume regions - cross section

  9. Plume structure - Day 8.3 (mean flow, no wind) Surface salinity Fresh water thickness

  10. Mixing and the Froude # Max. vertical salt flux Froude number

  11. Dynamically definedplume regions - cross section

  12. Plume structure Fresh water thickness Surface salinity Upwelling Upwelling Downwelling Downwelling

  13. Vertical salt flux - with wind upwelling downwelling No wind

  14. Integrated vertical salt fluxWind/no wind comparison Wind No wind

  15. Surface salinity - wind vs. none

  16. Gulf of MaineSea surface salinity Hetland & Signell

  17. Fresh water flux EMCC

  18. Fresh water flux WMCC

  19. Model skill of buoyancy driven coastal current transport

  20. Realistic model conclusions • While the model does not have high skill at point-by-point comparisons, the model is good at simulating the large ‘whole plume’ scale. • The model resolution is not high enough to resolve the estuary/near field regime, but still simulates the fresh water transport correctly. Wind forcing must reduce the sensitivity to the source

  21. Fresh water (salinity class) tmax= 0.1 m2 s-2 tmax= 0.2 m2 s-2 Qf = 1000 m3 s-1 Qf = 3000 m3 s-1

  22. Future direction • Idealized modeling: • How does wind control the plume salinity and spatial dimensions? • How do other types forcing (background flow, pulsing discharge) influence water mass modification by the wind. • Realistic modeling: • What are reasonable ranges in parameter space? • What is required to resolve the small-scale features of the plume?

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