Forecasting the dispersal of the Hudson River Plume

John WilkinGregg Foti

Byoung-Ju Choi

Institute of Marine and Coastal SciencesInstitute of Marine and Coastal SciencesRutgers, The State University of New JerseyRutgers, The State University of New Jersey

2005 ROMS Workshop2005 ROMS WorkshopSIO, San Diego 24-26 October, 2005SIO, San Diego 24-26 October, 2005

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

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

Bob Chant, John Wilkin, Bob Chant, John Wilkin, John Reinfelder, Scott Glenn, John Reinfelder, Scott Glenn, Oscar SchofieldOscar Schofield11, , Bob HoughtonBob Houghton22, Bob Chen, Bob Chen33, , Meng ZhouMeng Zhou33, Mark Moline, Mark Moline44, , Paul BissettPaul Bissett5 5 ,Tom Frazer,Tom Frazer66..

Lagrangian Transport and Lagrangian Transport and Transformation ExperimentTransformation Experiment

11Rutgers, Rutgers, 22Lamont-Doherty, Lamont-Doherty, 33U. Mass Boston, U. Mass Boston, 44FERI, FERI, 55Calpoly, Calpoly, 66U. Fla.U. Fla.

Lagrangian studies of the transport, transformation and biologicalimpact of nutrients and contaminant metals in a buoyant plume: A process study in an operational ocean observatory.

LaTTE: An interdisciplinary process study in an operational ocean observatory

R/V Cape Hatteras R/V Connecticut

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)

The Hudson River plume and adjacent shelf circulation in The Hudson River plume and adjacent shelf circulation in the New York Bight were forecast in support of the 2005 the New York Bight were forecast in support of the 2005 LaTTE field program using the LaTTE field program using the Regional Ocean Modeling Regional Ocean Modeling SystemSystem (ROMS) (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 u10 winds, Tair , qair , cloud, radiation from OPeNDAP server http://nomad3.ncep.noaa.gov:9090/dods/nam/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 wgetGNU 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/http://marine.rutgers.edu/~wilkin/wip/latte/

• Output data on OPeNDAP server http://queequeg.marine.rutgers.edu:9876/dodsC/latte/http://queequeg.marine.rutgers.edu:9876/dodsC/latte/

J. Wilkin

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'

LaTTE Pilot Experiment 2004

29-Apr-2004 15:24 – 30-Apr-2004 04:28

01-May-2004 21:52 – 02-May-2004 19:31

RU02 – Hudson River Plume

South North

West East

LaTTE Pilot Experiment 2004

3 May 2004

Freshwater plume that carried first dye injection east and onto the Long Island shore

Second dye injection into coastal current

Re-circulation feature related to freshwater anomaly and bottom flow steered by bathymetry

Wind change reversed coastal current and redirected Hudson outflow to east

LaTTE Experiment 2005

OCM visible RGB and CODAR 09-Apr-2005 16:90 UT

Observations ModelObservations Model

ROMS salinity and velocity

at 2m 09-Apr-2005

OCM visible RGB and CODAR 18-Apr-2005 15:38 UT

ROMS salinity and velocity at 2m 18-Apr-2005

J. Wilkin

1 day average 19-Apr-2005

LaTTE Experiment 2005

Real-time forecast dye trajectory: second injectionReal-time forecast dye trajectory: second injection

LaTTE Experiment 2005

G. Foti and J. Wilkin

ho

o dzS

SSThe horizontal dispersal of the The horizontal dispersal of the freshwater anomaly due to the plume freshwater anomaly due to the plume can be visualized in terms of the can be visualized in terms of the equivalent freshwater depth:equivalent freshwater depth:

J. Wilkin

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:

B.-J. Choi and J. Wilkin

Fong and Geyer (2002)

Plume response under idealized wind scenarios Plume response under idealized wind scenarios

For high river For high river discharge typical discharge typical of the spring of the spring freshet, a set of freshet, a set of idealized wind idealized wind forcing forcing simulations shows simulations shows how the plume how the plume responds to wind responds to wind direction.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

Westerly wind directs plume toward Hudson Shelf Valley

Easterly wind arrests plume

For high river For high river discharge typical discharge typical of the spring of the spring freshet, a set of freshet, a set of idealized wind idealized wind forcing forcing simulations shows simulations shows how the plume how the plume responds to wind responds to wind direction.direction.

B.-J. Choi and J. Wilkin

Plume response under idealized wind scenarios Plume response under idealized wind scenarios

April 2-18 average

April 2-18 average

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

• 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

Summary