Forecasting the dispersal of the Hudson River Plume John Wilkin Gregg Foti Byoung-Ju Choi

1. Forecasting the dispersal of the Hudson River PlumeJohn WilkinGregg FotiByoung-Ju Choi Institute of Marine and Coastal SciencesRutgers, The State University of New Jersey 2005 ROMS WorkshopSIO, San Diego 24-26 October, 2005

2. Coastal ocean modeling: Analysis and prediction • Coastal ocean is a filter • nutrients and sediments from rivers and atmosphere • majority are re-mineralized with little export to the deep ocean • U.S. East Coast: • discharge of many rivers is modified in estuaries • Chesapeake Bay: • assimilation by plankton and export as inorganic nitrogen • New York: • 90% nitrogen is exported unassimilated onto the shelf • NY/NJ Harbor sediments are ~4% of MAB load, but carry 90% of PCBs and 70% of mercury • Where it goes and how it is transformed depends not biology, geochemistry and physics

3. Visible image from Aqua 6-Apr-2005 18:30 UT

4. Lagrangian Transport and Transformation Experiment Lagrangian studies of the transport, transformation and biological impact of nutrients and contaminant metals in a buoyant plume: A process study in an operational ocean observatory. Bob Chant, John Wilkin, John Reinfelder, Scott Glenn, Oscar Schofield1, Bob Houghton2, Bob Chen3, Meng Zhou3, Mark Moline4, Paul Bissett5 ,Tom Frazer6. 1Rutgers, 2Lamont-Doherty, 3U. Mass Boston, 4FERI, 5Calpoly, 6U. Fla.

5. LaTTE: An interdisciplinary process study in an operational ocean observatory

6. R/V Cape Hatteras R/V Connecticut

7. ROMS modeling of the Hudson River plume: • develop intuition – a Latte playbook (Choi) • forecasts for adaptive sampling during field operations (Foti) • the shear geeky pleasure of the adjoint model (Zhang, Levin) • post-experiment analysis (all of us)

8. The Hudson River plume and adjacent shelf circulation in the New York Bight were forecast in support of the 2005 LaTTE field program using the Regional Ocean Modeling System (ROMS) http://marine.rutgers.edu/roms • Operational model configuration: • Domain: • central Long Island to mouth of Delaware Bay, out to approximately the 100-m isobath • 1 km horizontal resolution; 30 vertical s-levels • Forcing: • NCEP NAM-ETA hourly forecast u10winds, Tair , qair , cloud, radiation from OPeNDAP server http://nomad3.ncep.noaa.gov:9090/dods/nam/ • Daily mean Hudson River flow from USGS Mohawk and Fort Edward gauges + persistence (for forecast) accessed via web using GNU wget • Boundary tides from ADCIRC, tuned by assimilation of local tidal harmonic data • No boundary mean flow or pressure gradient at open boundaries • Output: • Model runs daily to generate 48- to 60-hour forecast • Output graphics for 2005 at http://marine.rutgers.edu/~wilkin/wip/latte/ • Output data on OPeNDAP server http://queequeg.marine.rutgers.edu:9876/dodsC/latte/ J. Wilkin

9. LaTTE Pilot Experiment 2004 2004 Dye Injections Injection 1 • May 2nd, 2004 • 14:54 GMT – 15:03 GMT • 40° 31.48' 73° 46.6' Injection 2 • May 4th, 2004 • 13:42 GMT – 14:00 GMT • 40° 21.9' 73° 54.8'

10. West East South North RU02 – Hudson River Plume LaTTE Pilot Experiment 2004 29-Apr-2004 15:24 – 30-Apr-2004 04:28 01-May-2004 21:52 – 02-May-2004 19:31

11. 3 May 2004

12. Second dye injection into coastal current Freshwater plume that carried first dye injection east and onto the Long Island shore Re-circulation feature related to freshwater anomaly and bottom flow steered by bathymetry Wind change reversed coastal current and redirected Hudson outflow to east

13. LaTTE Experiment 2005

14. OCM visible RGB and CODAR 09-Apr-2005 16:90 UT ROMS salinity and velocity at 2m 09-Apr-2005 Observations Model OCM visible RGB and CODAR 18-Apr-2005 15:38 UT ROMS salinity and velocity at 2m 18-Apr-2005 J. Wilkin

15. 1 day average 19-Apr-2005

16. LaTTE Experiment 2005

17. LaTTE Experiment 2005 Real-time forecast dye trajectory: second injection G. Foti and J. Wilkin

18. The horizontal dispersal of the freshwater anomaly due to the plume can be visualized in terms of the equivalent freshwater depth: J. Wilkin

19. The modeled plume trajectory is dependent on local winds. Modeled dynamical term balances show that direct downstream forcing by the buoyancy pressure gradient force is small compared to surface wind stress. No wind simulation – freshwater ‘bulge’ continues to grow: Fong and Geyer (2002) B.-J. Choi and J. Wilkin

20. Plume response under idealized wind scenarios For high river discharge typical of the spring freshet, a set of idealized wind forcing simulations shows how the plume responds to wind direction. Southerly directs plume north of Hudson Shelf Valley and toward Long Island Northerly amplifies coastal current and drains freshwater bulge B.-J. Choi and J. Wilkin

21. Plume response under idealized wind scenarios For high river discharge typical of the spring freshet, a set of idealized wind forcing simulations shows how the plume responds to wind direction. Westerly wind directs plume toward Hudson Shelf Valley Easterly wind arrests plume B.-J. Choi and J. Wilkin

28. April 2-18 average

29. April 2-18 average

30. The sensitivity of sea surface temperature (arbitrary units) in the marked triangular box to SST over the preceding half day for an idealized simulation of low Hudson River flow in the inner New Jersey/New York Bight region, computed using the ROMS Adjoint model. G. Zhang, J. Levin and J. Wilkin

31. Summary • ROMS prediction system • with NCEP/NAM atmospheric forecast • observed river flows • Reasonable simulations of the dispersal of the spring freshet during the LaTTE April 2005 observing period • no assimilation • OK for a locally forced regime • Flow is responsive to local winds on short time scales • Relatively little low salinity water immediately traveled southward as a coastally trapped buoyancy driven current • The coastal current only forms with the assistance of favorable winds • The Hudson Shelf Valley exerts control on the overlying circulation • Much of the freshwater is dispersed eastward along the L.I. coast • Some heads offshore along the south flank of the Hudson Shelf Valley