Local and deep-ocean forcing contributions to anomalous water

properties on the WFS

Robert Weisberg and Ruoying He

College of Marine ScienceUniversity of South Florida

St. Petersburg, FL

HYCOM P.I. Mtg.8/19/03

Approach

A Coordinated Program of:

1) In-situ Measurements:(Sea level, Currents, Winds, Surface heat fluxes, Rivers,

Temperature, Salinity, Nutrients, Primary productivity andother biological indicators)

and

2) Models:(Ocean Circulation and Ecology)

Desoto Canyon

Loop Current

Mississippi River

Mobile River

Apalachicola RiverSuwannee River

Hillsborough River

Shark River

Peace River

Wind

Heat FluxLocal forcing:Local forcing:•• WindsWinds•• Surface heat fluxSurface heat flux•• River runoffsRiver runoffs

Deep Ocean forcing:Deep Ocean forcing:•• Loop Current and Loop Current and adjacent wateradjacent water

Loop CurrentLoop Current

To simulate the Loop Current interacting with the To simulate the Loop Current interacting with the shelfshelf--break, we control S.L. along the boundary.break, we control S.L. along the boundary.

Up and Downwelling

sequence at theDeSoto Canyon

Transect

Type 1June 2000

Loop CurrentLoop Current

(1) (2) (3) (4)(1) (2) (3) (4)

10 years Time series of Topex/Poseidon Data10 years Time series of Topex/Poseidon Data

25o N

Loop CurrentLoop Current

Track 26

Track 26

Type 2

(1) October 1996 October 1996 –– February, 1997February, 1997(2) June 1997 (2) June 1997 –– November 1997November 1997(3) March 1998 (3) March 1998 –– July 1998 July 1998 (4) September 1998 (4) September 1998 –– November 1998November 1998

Hetland R.D. et al , A Loop Current induced jet along Hetland R.D. et al , A Loop Current induced jet along the edge of west Florida shelf, the edge of west Florida shelf, Geophys. Res. LettGeophys. Res. Lett. 1999. 1999

Local forcing onlyLocal forcing only Local forcing + LCLocal forcing + LC

Bottom Ekman layer currents transport these waters to the coast.

18º

(A)(A)

(B)(B)

Cold, nutrient-rich water upwells onto the shelf by thecombined effects of local and LC forcing.

Lagrangian trajectories for near bottom,

neutrally buoyant particles released

on the 50m and 100misobaths in

summer 1998

Vertical Velocity at mid-depth on 05/15/98

Vertical Velocity alongSarasota Transect on05/15/98

OI analysis of EDAS and Buoy windsOI analysis of EDAS Winds

Model and observed across-shelf momentum analysis

Modeled and observed along-shelf momentum analysis

Summary1. WFS currents result from both local and deep-ocean

forcing.

2. Deep-ocean forcing sets the height of materialisopleths at the shelf-break and under specialconditions can also set shelf currents in motion.

3. Local forcing drives offshore properties onto the shelf.

4. The bottom Ekman layer is the conduit for the across-shelf transport of nutrient rich waters upwelled at the shelf-break.

5. Inter-annual variations in local and deep-ocean forcing cause inter-annual variations in WFS ecology.

References and WebsitesWeisberg, R.H. and R He (2003). Local and deep-ocean

forcing contributions to anomalous water properties on the West Florida Shelf. J. Geophys. Res., 108, C6, 15, (doi10.1029/2002JC001407).

Walsh, J.J. et al. (2003). Phytoplankton response to intrusions of slope water on the West Florida Shelf. J. Geophys. Res., 108, C6, 21, (doi10.1029/2002JC001406).

Data and other products from R.H. Weisberg’s group at USF

http://ocg6.marine.usf.edu

Real time data from the COMPS Programhttp://comps.marine.usf.edu

Some Other Activities

1. A SEA-COOS domain modeling effort.

2. Application of a finite volume model to the WFS for the purpose of linking the estuaries with the shelf.

3. Comparative hindcast studies using POM, FVM, and ROMS.

Tampa Bay

Charlotte Harbor

Zoom view of Tampa Bay, Charlotte Harbor, and the inner-shelf