Transcript Numerical Modeling Study on the West Florida Shelf

WEST FLORIDA SHELF
Physical Oceanography
Robert Weisberg
HyCODE P.I. Mtg, 1/7/02
Objectives and Applications
Objectives:
1) Determine how physical processes affect
material property distributions on the WFS
2) Determine the relative importance of deep ocean
forcing (by the LC and its eddies) and local forcing
by winds and buoyancy fluxes.
Applications:
Biological - Red tide, fish larvae
Chemical - Nutrients
Geological - Sediment resuspension and transport
Physical - Currents, sea level, T/S
Approach
• Our approach combines in-situ measurements with
numerical circulation modeling
• Measurements are by moorings, ships, and satellite
• Modeling is by regional adaptations of the POM
Problem Definition
Desoto Canyon
Mobile River
Apalachicola River
Suwannee River
Mississippi River
Wind
Heat Flux
Hillsborough River
Peace River
Loop Current
Shark River
Accomplishments
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Moored arrays: 1993-1998
Moored array: 6/98-12/01
Scaled down moored array: 12/01-present
Hydrography: 6/98-12/01
Real-time data
Model: Mississippi River to Florida Keys
Nowcast-Forecast Shelf Circulation Model
Publications
Research Results
INNER SHELF DEFINITION

Three-dimensionality and the essential role
played by stratification


Ref.
Weisberg et al. (2001) West Florida shelf response to local
forcing: April 1998. Jour. Geophys. Res., in press
April 1998 measurement
 Along-shelf velocity
 Across-shelf velocity
 Sea level at St.
Petersburg
 Wind velocity
 Wind stress
Spring Season Transitional
Circulation: The Cold Tongue
and the “Green River”

Local forcing versus the LC
 The dual role of winds and surface heat flux

Refs.

Weisberg et al. (1996) Geophys. Res. Lettrs., 23, 2247-2250.

He and Weisberg (2001) Cont. Shelf Res., in press
• Princeton Ocean Model
(2-6 km resolution, 21 layers)
• Driven by NCEP reanalysis
wind and surface heat fluxes
and river inflow
• Radiation condition along the
OB. e.g., the Loop Current is
excluded
• Comparisons are made between
the modeled and observed sea level
and current
Sea Level Comparisons
Data (thin line)
Model (thick line)
The coastal sea level
responds primarily to
local, shelf-wide forcing
Current time series from Model and data
at surface, mid-depth and near bottom
Seasonal Mean Current
Vectors and variance ellipses
wind
Surface
current
Mid-depth
current
Bottom
current
Black (Model); Red (Data)
Seasonal mean depth
average current
Middle
Shelf jet
Model Sea Surface Temperature
May 31
Modeled Sea Surface Salinity
May 31
“Cold
Tongue”
“Green
River “
Evolution of monthly mean flow fields
Early Spring
Heat flux
cold
colder
warm
Late Spring
Heat flux
cold
warm
warm
T
T
T
T  
T   
T   
T 

 u
v
w
  KH
   AH
   AH
t
x
y
Z z 
z  x 
x  y 
y 
Local change
Advection
Ocean circulation
Vertical and Horizontal Diffusion
primarily surface heat flux


=local change
h
Mean (diffusion) > Mean (advection); Std (diffusion) < Std (advection)
Tides on the WFS

Barotropic tides
 Four major tidal constituents (M2, S2, K1 and O1)


Ref:
He and Weisberg, 2002, Tides on the West Florida Shelf
Submitted to Journal of Physical Oceanography
Observed
Tidal current
ellipses
Modeled
Tidal current
ellipses
Loop Current vs
Local Forcing Influences

The effect of Loop Current forcing on the shelf
superimposed upon
 the effect of Local wind forcing on the shelf.


Refs:
He and Weisberg, 2002, A Loop Current intrusion case study on the West
Florida Shelf, manuscript submitted JPO.
 Li and Weisberg, 1999a, West Florida shelf response to upwelling favorable
wind forcing, Part I. Kinematic description. Jour. Geophys. Res., 104, 1350713527.
 Li and Weisberg, 1999b, West Florida shelf response to upwelling favorable
wind forcing, Part II. Dynamics analyses. Jour. of Geophys. Res., 104, 2343723442.
Daily SST June 1 – July 6, 2000
Southward
Geostrophic Current
Daily subsurface Current map June 1 – July 6, 2000
“Mature
Phase”
“Young
Phase “
LC only
LC only
LC +
Upwelling
wind
LC +
Downwelling
Wind
LC +
Upwelling
wind
LC +
Downwelling
wind
Inter-annual variability of the
WFS circulation

Inter-annual variability in the circulation
as accounted for by
 Local and offshore forcing

Ref:
Weisberg and He (2002). Anomalous circulation on the west
Florida shelf: Local and offshore influences.
Inter-annual variability
In the local wind forcing
Time Series of Topex SSH Anomaly Along Track 26
ADCP Current Measurements
(PA 30m, CM 50m and
LB 20m)
Local Forcing
Only
Spring 1998
Local Forcing
Only
Spring 1999
Local Forcing
Only
Local Forcing
Only
+
Loop Current
Spring 1998
Spring 1998
Current at 30 m in Spring and Summer 1998
Local forcing only
Local forcing +LC
Current at 50 m in Spring and Summer 1998
Local forcing only
Local forcing+LC
Current at 20 m in Spring and Summer 1998
Local forcing only
Local forcing +LC
8/5
3/30
200m
USF
30m (Mote)
9/9
5/18
50m USF
30m (Mote)
11/9
6/10
200m
USF
7/7
200m
USF
200m
USF
Temperature Along Mote,
USF Sarasota, Tampa
Transects between March
And November 1998
Summary
• Collected in-situ data: currents, sea level, hydrography, surface
met., including a real time network (COMPS).
• Developed a regional circulation model (Miss. River to FL. Keys)
for hindcast studies and for coupling with a biological model.
• Developed a regional nowcast-forecast circulation model.
• Performed model-data comparisons for tidal, synoptic,
seasonal, and inter-annual time scales.
• Local forcing, independent of the Loop Current and eddies,
accounts for much of the WFS variability, including the spring
cold tongue and “Green River”.
• The Loop Current modifies the effects of local forcing, primarily
by setting the height of material surfaces at the shelf break.
Occasionally, when impinging at the southern edge, the LC also
sets the inner-shelf in motion.
• The circulation, and its control on material property distributions,
is fully three-dimensional.
• An asymmetry occurs between upwelling and downwelling wind
responses due to inner-shelf control by the bottom Ekman layer.