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 Idealized modeling Realistic modeling Numerical consistency Physical consistency Metrics (Depends on user requirements)

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 defined plume regions - cross section

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

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

11. Dynamically defined plume regions - cross section

12. Plume structure UpwellingDownwelling Upwelling Surface salinity Fresh water thickness

13. Vertical salt flux - with wind upwellingdownwelling No wind

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

15. Surface salinity - wind vs. none

16. Gulf of Maine Sea surface salinity Hetland & Signell

17. Fresh water flux EMCC

18. Fresh water flux WMCC

19. Model skill of buoyancy driven coastal current transport EMCCWMCC 33 hr7 day33 hr7 day Along-shore currents-0.410.01-0.87-0.74 Cross-shore currents-1.06-0.46-0.510.57 Surface salinity-0.47-0.360.830.98 Fresh water flux0.520.860.030.66

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) Q f = 1000 m 3 s -1  max = 0.1 m 2 s -2 Q f = 3000 m 3 s -1  max = 0.2 m 2 s -2

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?