SABLAM Group (NOPP, 2000)
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Transcript of SABLAM Group (NOPP, 2000)
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Development of an operational coastal
ocean observing system for the South
Atlantic Bightor
Operational modeling – what’s it gonna take? An
attempt in the SAB
The SABLAM group
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SABLAM Group (NOPP, 2000)
• Dartmouth: Dan Lynch, [Chris Naimie], Keston Smith, Jeff Proehl
• UNC-CH: Cisco Werner, Rick Luettich, Brian Blanton, Alfredo Lopez de Aretxabaleta, Luke Stearns, Harvey Seim
• WHOI: Dennis McGuillicuddy• SkIO: Jim Nelson, Trent Moore• [MCNC: Eric Sills]• JAX, CHA WFO: Pat Welsh, [Stephen
Brueske][ ] – no longer participating
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SABLAM Objective
To develop a portable, limited-area modeling system that provides an operational forecast of conditions in the coastal ocean that includes the influence of tides, local air-sea interactions, buoyancy and remote forcing.
Tall order. Requires….
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A coastal ocean observing system
Modeling perspective
•Climatology•Eventually, (soon) HYCOM/GODAE
Initialization
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Nested Meteorological/Ocean Models
SAB Climatology
HYCOM or COFSBaroclinic/Gulf Stream Forcing
ADCIRC DomainFar-Field Tide and
Wind-Band Forcing
SABLAM DomainQUODDY
TRUXTON/CASCOLimited-Area Shelf Models,
Data Assimilative
AWIP 32 Domain10 km ETAMet. Model
High Resolution, RegionalETA Model
Improved Air/Sea Interaction
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Will examine some of the stumbling blocks encountered in SABLAM:
Getting a good priorBarotropic dynamics: tidal, weather band, lower
frequency
Baroclinic dynamics (density field): from climatology, SST/in-situ obs, basin-scale models
Assimilation - a technique to minimize difference between sparse observations and simulated fields
Three components: frequency domain inverse,time domain inverse, objective analysis
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Barotropic tides: should be straightforward…
•Finite Element•2D (ADCIRC)•Time-dependent•Fully Nonlinear•Elev. BCs from Global FES95D
Performswell exceptin SAB
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Problem: typical coastal tide station
is not “in” the typical shelf model domain
Fort Pulaski, GA
Landward Bndy of Operational models
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In the SAB large sections of the coastline are backed by extensive
estuaries
No Estuary
Boundary
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This coastal geometry is concentrated between central
SC and north FL
“No Estuary”
Boundary
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•Finite Element •Nonlinear•2D (ADCIRC)•Western North Atl.•Crossshelf Amplification•Equatorward phase propagation •Latest phase along GA/FL border
•Shelf response sensitive
NC
SC
FL
GA
M2 Elevation Prior without estuaries – tide experiences
two-fold amplitude increase and notable phase change
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M2 Obs Vs. Prior, without Estuaries
Larger phase error closer to shore
Amplitude (m) Phase (deg)
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M2 Obs Vs. Prior, with Estuaries
Substantially reduced phase error closer to shore
Amplitude (m) Phase (deg)
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M2 Phase Comparison
RED = without EstuariesBLUE = with Estuaries
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FL
RED = without estuariesBLUE = with estuaries
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Implication: different M2 energy flux required to support estuarine dissipation
Operationally:need unstructuredgrids or true two-way coupling toaccurately representtide along thistype of coastline
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Nontidal prior response – from 2D wind-forced model of western North Atlantic. Comparison of detided CSL at Mayport, FL
Observed CSL Modeled CSL
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Weather-band (<15 day) comparison favorable; some under-estimate during large events…
Observed CSL Modeled CSL
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Consistentwith under-estimate oflongshorewinds seenin ETA predictions(cross-shoreand tempslook OK)
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Observed CSL Modeled CSL
At lower frequencies (>15 day) the comparison is less favorable; see some 25 cm offsets; partly steric but…
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Blaha, JGR ’84 (?)found coherent monthly averagedsea level variationsover SAB (’55-’75 period, heatingand atmos. presseffects removed).Can be more than 20 cm variation annually. Postulated due toGulf Stream transportvariations.
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Noble/Gelfenbaum – modeled coastal SL impact of GS transport variations.
Coast
Shelf
Gulf Stream
Average transport
Low transport
Offshore Fixed “Hinge”
Coast
Shelf
Gulf Stream
High transport
Average transport
Offshore Fixed “Hinge”
Low transport,higher CSL
High transport,lower CSL
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Baringer/Larsen
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Climatology (3)
Objective analysis digital analog to Atkinson et.al. (1983)
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TEMP
SALN
t
Climatology (5)Cross-shelf Structure from Objective
Analysis
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Climatology (7)Monthly Mean COADS Winds Only
Monthly BaroclinicSolution
Winds + BC
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Climatology …
Charleston Bump½ x ½
deg squares
Bottom depth:
<400m
>400m
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GODAE into SABLAM
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Micom D180
•Mid summer
•Reanalysis
•Unrealistic
upwelling
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Data Assimilation System
Wind+Tide
Data Assimilative Loop (1)
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Data Assimilative Loop (2) Far-Field computation of Wind+Tide
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Data Assimilative Loop
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SABSOON/SABLAM Data
East Coast Domain for Tidal/Wind-Driven BCs for Limited-Area Mesh
Nested SABLAM Mesh for Hindcast/Forecast System
Obs. Locations:
Water Level
SABSOON ADCP
NC
SC
GA
FL
3000m
1000m
200m
50m25m
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M2 Phase Comparison
GA
FL
RED = W/O EstuariesBLUE = W/ Estuaries
>3
Phas
e D
iff.
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Lower Mean Sealevel
Coast
Shelf
Gulf Stream
Higher Transport
Average Transport
Offshore Fixed “Hinge”
xnV
Increased Transport
Increased Cross-stream Slope
LOWER Coastal Sea level
Noble/Gelfenbaum
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Higher Mean Sealevel
Coast
Shelf
Gulf Stream
Average Transport
Lower Transport
Offshore Fixed “Hinge”
xnV
Decreased Transport
Decreased Cross-stream Slope
HIGHER Coastal Sealevel
Noble/Gelfenbaum
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