Development of an operational coastal ocean observing system for the South Atlantic Bight or Operational modeling – what’s it gonna take? An attempt in the SAB The SABLAM group

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

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….

A coastal ocean observing system Modeling perspective Climatology Eventually, (soon) HYCOM/GODAE Initialization

Nested Meteorological/Ocean Models SAB Climatology HYCOM or COFS Baroclinic/Gulf Stream Forcing ADCIRC Domain Far-Field Tide and Wind-Band Forcing SABLAM Domain QUODDY TRUXTON/CASCO Limited-Area Shelf Models, Data Assimilative AWIP 32 Domain 10 km ETA Met. Model High Resolution, Regional ETA Model Improved Air/Sea Interaction

Will examine some of the stumbling blocks encountered in SABLAM : Getting a good prior Barotropic 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

Barotropic tides: should be straightforward… Finite Element 2D (ADCIRC) Time-dependent Fully Nonlinear Elev. BCs from Global FES95D Performs well except in SAB

Problem: typical coastal tide station is not “in” the typical shelf model domain Fort Pulaski, GA Landward Bndy of Operational models

In the SAB large sections of the coastline are backed by extensive estuaries No Estuary Boundary

This coastal geometry is concentrated between central SC and north FL “No Estuary” Boundary

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 M 2 Elevation Prior without estuaries – tide experiences two-fold amplitude increase and notable phase change

M 2 Obs Vs. Prior, without Estuaries Larger phase error closer to shore Amplitude (m)Phase (deg)

M 2 Obs Vs. Prior, with Estuaries Substantially reduced phase error closer to shore Amplitude (m)Phase (deg)

M 2 Phase Comparison RED = without Estuaries BLUE = with Estuaries

FL RED = without estuaries BLUE = with estuaries

Implication: different M 2 energy flux required to support estuarine dissipation Operationally: need unstructured grids or true two- way coupling to accurately represent tide along this type of coastline

Nontidal prior response – from 2D wind-forced model of western North Atlantic. Comparison of detided CSL at Mayport, FL Observed CSLModeled CSL

Weather-band (<15 day) comparison favorable; some under-estimate during large events… Observed CSLModeled CSL

Consistent with under- estimate of longshore winds seen in ETA predictions (cross-shore and temps look OK)

Observed CSLModeled CSL At lower frequencies (>15 day) the comparison is less favorable; see some 25 cm offsets; partly steric but…

Blaha, JGR ’84 (?) found coherent monthly averaged sea level variations over SAB (’55-’75 period, heating and atmos. press effects removed). Can be more than 20 cm variation annually. Postulated due to Gulf Stream transport variations.

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

Baringer/Larsen

Climatology (3) Objective analysis digital analog to Atkinson et.al. (1983)

TEMP SALN tt Climatology (5) Cross-shelf Structure from Objective Analysis

Climatology (7) Monthly Mean COADS Winds Only Monthly Baroclinic Solution Winds + BC

Climatology … Charleston Bump ½ x ½ deg squares Bottom depth: <400m >400m

GODAE into SABLAM

Micom D180 Mid summer Reanalysis Unrealistic upwelling

Data Assimilation System Wind+Tide Data Assimilative Loop (1)

Data Assimilative Loop (2) Far-Field computation of Wind+Tide

Data Assimilative Loop

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 50m 25m

M 2 Phase Comparison GA FL RED = W/O Estuaries BLUE = W/ Estuaries >3 Phase Diff.

Lower Mean Sealevel Coast Shelf Gulf Stream Higher Transport Average Transport Offshore Fixed “Hinge” Increased Transport Increased Cross-stream Slope LOWER Coastal Sea level Noble/Gelfenbaum

Higher Mean Sealevel Coast Shelf Gulf Stream Average Transport Lower Transport Offshore Fixed “Hinge” Decreased Transport Decreased Cross-stream Slope HIGHER Coastal Sealevel Noble/Gelfenbaum