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WORKSHOP ON HYPOXIA IN NARRAGANSETT BAY OCTOBER 2 , 2006 - FIELDWORK IN SUPPORT OF HYDRODYNAMIC MODELS. Large Scale CTD Surveys - Deacutis, Murray, Prell Moored + Vessel-based Circulation Studies – Kincaid, Bergondo Towed Undulator Surveys - Ullman

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slide1

WORKSHOP ON HYPOXIA IN NARRAGANSETT BAY

OCTOBER 2 , 2006

- FIELDWORK IN SUPPORT OF

HYDRODYNAMIC MODELS

  • Large Scale CTD Surveys - Deacutis, Murray, Prell
  • Moored + Vessel-based Circulation Studies – Kincaid, Bergondo
  • Towed Undulator Surveys - Ullman
  • Moored Vertical Profilers – Vaudrey, Kremer
slide2

“The Day Trippers”

– Large Scale CTD Surveys 2006

Survey Dates :

Neap Tide Surveys :

6/6/06, 7/6/06, 8/3/06,8/31/06

Spring Survey : 8/11/06

slide7

PRN 1

PRS 07

http://www.geo.brown.edu/georesearch/insomniacs/

slide16

Summary Bottom Mounted Results

  • EYC shallows – average surface flow to North
      • Influenced by prevailing winds
  • Two layer flow in EYC and Conimicut channels
      • Southward winds enhance return flow
      • Northward winds stall return flow
slide17

Physics: Observations & Modeling

Acoustic Doppler Current Profilers - C Kincaid

Bottom mounted

Ship mounted

Data coverage:

Excellent temporal

Poor Spatial

Data coverage:

Good spatial

Poor Temporal

slide18

Results: Providence River

Prevailing outflow - shallow, western side shipping channel

Prevailing inflow - deep, eastern side shipping channel

Series of weak, recirculation eddies in shallow edges

Strong wind-induced water column response/reorientation

Physics:

Goal to characterize circulation, mixing, flushing, transport, etc

Methods are Observations & Modeling

slide19

Bay Circulation Data Summary: Model boundary conditions

18 underway surveys: summer vs winter

slide20

Bay Circulation Data Summary: Model boundary conditions

18 underway surveys: summer vs winter

1.5 years of BM-ADCP data

slide21

Bay Circulation Data Summary: Model boundary conditions

Summer: strong long-shore flow

bottom

surface

slide22

Bay Circulation Data Summary: Model boundary conditions

Summer: prevailing (depth-averaged) counter-clockwise flow

Summer: strong long-shore flow

slide23

Bay Circulation Data Summary: Model boundary conditions

Summer: prevailing (depth-averaged) counter-clockwise flow (CCF)

Dominant exchange through mouth

Summer: strong long-shore flow

slide25

Bay Circulation Data Summary: Model boundary conditions

Extent of counter

Wind

Strong wind-induced exchanges

SE winds enhance CCF, trigger RIS intrusion

slide26

Bay Circulation Data Summary: Model boundary conditions

Extent of counter

Spatial extend of CCF

?

?

Wind

Strong wind-induced exchanges

SE winds enhance CCF, trigger RIS intrusion

slide27

Bay Circulation Data Summary: Model boundary conditions

Extent of counter

Winter: Strong 2-layer flow

RIS water from southwest

slide28

Bay Circulation Data Summary: Model boundary conditions

Mt. Hope Bay circulation/exchange

/mixing study. ADCP, tide gauges

(Deleo, 2001)

Extent of counter

Bay-RIS exchange study (98-02)

slide29

Bay Circulation Data Summary: Model boundary conditions

Narragansett Bay Commission: Providence & Seekonk Rivers

Mt. Hope Bay circulation/exchange

/mixing study. ADCP, tide gauges

(Deleo, 2001)

Extent of counter

Bay-RIS exchange study (98-02)

slide30

This project: Mid-Bay focus

Narragansett Bay Commission: Providence & Seekonk Rivers

Mt. Hope Bay circulation/exchange

/mixing study. ADCP, tide gauges

(Deleo, 2001)

Extent of counter

Summer, 07: 4 month deployment (Outflow pathways)

Bay-RIS exchange study (98-02)

slide31

This project: Mid-Bay focus

Outflow, inflow, exchange between Bay sub-regions

Narragansett Bay Commission: Providence & Seekonk Rivers

Mt. Hope Bay circulation/exchange

/mixing study. ADCP, tide gauges

(Deleo, 2001)

Extent of counter

Summer, 08: Deep return flow processes

Bay-RIS exchange study (98-02)

high resolution surveys of hydrography currents and vertical mixing
High-Resolution Surveys of Hydrography, Currents, and Vertical Mixing

Dave Ullman (GSO)

  • Objectives:
    • Provide high resolution sections of physical
    • and biological parameters for assessment and
    • calibration of hydrodynamic and ecological models.
    • Estimate vertical turbulent mixing rates.
  • Methodology:
    • Towed undulating vehicle measuring hydrographic
    • parameters and turbulent microstructure.
    • Shipboard ADCP measuring currents.
towed undulating vehicle

Acrobat

Microstructure

Sensors.

Towed Undulating Vehicle
  • Towed vehicle sensors:
  • Temperature
  • Conductivity
  • Pressure
  • Oxygen concentration
  • Chlorophyll fluorescence
  • Nitrate concentration
  • Microscale conductivity
  • (turbulent mixing)
  • Ship-mounted ADCP:
  • Velocity profiles
along channel sections suggest dynamical importance of the narrows at conimicut
Along-channel sections suggest dynamical importance of the “narrows” at Conimicut

Rapid variability in depth of

thermocline, halocline over short

distances.

Conimicut

intensive sampling conimicut region

Coordinate origin

Conimicut Pt.

Intensive Sampling, Conimicut Region
  • Carried out repeated tows over approximately a full tidal cycle
  • along black line shown on bathymetry map:
    • August 11, 2005 (Neap): 18 lines
    • August 18, 2005 (Spring): 20 lines
flood tide eddies
Flood Tide Eddies
  • Commonly observed just south of narrows at Conimicut on flood tide.
  • Cause as yet unknown.
  • Potential to be an important horizontal dispersal mechanism.

Aug. 11, 2005 early flood

Clockwise eddy in

near-surface current

(blue vectors)

Extends down

to ~7 m depth.

East Component (m/s)

North Component (m/s)

Conimicut

south

signature of eddies in hydrographic fields

Acrobat

Signature of Eddies in Hydrographic Fields?

T

Doming of isolines in upper water

column in eddy region.

S

ADCP

Eddy

East Component (m/s)

O2

Chl-a

North Component (m/s)

NO3

vertical mixing estimates
Vertical Mixing Estimates
  • Methodology:
    • Compute variance of conductivity gradient.
    • Apply corrections for salinity contributions
    • and sensor response to get temperature
    • gradient variance.
    • Dissipation rate of temperature gradient
    • fluctuations (T) is proportional to variance.
    • Estimate vertical temperature gradient ( )
    • from CTD sensors on acrobat.
    • Turbulent thermal eddy diffusivity
    • computed from T and gradient:
  • Micro-conductivity Sensor on Acrobat:
  • Measures conductivity at scales of O(1cm).
  • Sampled at 1024 Hz.
example vertical diffusivity section
Example Vertical Diffusivity Section

From a single tow on Aug. 18, 2005.

Spring tide conditions, ebb flow.

Colors: log10(KT) (m2/s)

Lines: t (kg/m3)

  • Conimicut narrows:
    • KT~10-4 - 10-3 m2/s
    • (strong vertical mixing)

south

tidally averaged vertical turbulent diffusivity
Tidally Averaged Vertical Turbulent Diffusivity

Colors: log10(KT) (m2/s)

Lines: t (kg/m3)

Aug. 11 (neap)

Aug. 18 (spring)

  • Turbulent mixing appears to be enhanced in the Conimicut area.
  • Slightly stronger mixing on spring tides:
    • Neap average = 2.9x10-5 m2/s.
    • Spring average = 3.5x10-5 m2/s.
future interaction with modelers
Future Interaction with Modelers
  • Compare observations to ROMS model output:
    • Tidal eddies
      • Present in model?
      • If so, what is the mechanism by which they form?

(Examine model momentum balance)

      • How do they affect horizontal property transport?
    • Vertical mixing
      • How does magnitude of model vertical mixing

(computed by turbulence closure submodel) compare

with observed mixing rates?

      • Can observations be used to tune model turbulence

parameterizations?

    • Stratification
      • Is model vertical stratification of similar magnitude

as observed?

slide42

J. Kremer & J. Vaudrey

Profiling Units

4 Locations

Field’s Point

Bullocks Reach Buoy

east of Conimicut Point Light

Warwick Neck

Sampling Set-Up

sample every 15cm in the vertical

1 profile every 3 hours

deployed for ~ 2 weeks

3 Deployments

June, July, September

slide44

Temperature

oC

depth off the bottom (m)

Salinity

ppt

Dissolved

Oxygen

mg/L

day of deployment (day 1 = 8/31/06)

east of Conimicut Light

slide46

Warwick Neck

Temperature

oC

depth off the bottom (m)

Salinity

ppt

Dissolved

Oxygen

mg/L

day of deployment (day 1 = 6/27/06; day 16 = 7/13/06)

slide50

Hydrodynamic Model

Grid Resolution: 100 m

Grid Size: 1024 x 512

Vertical Layers: 20

River Flow: USGS

Winds: NCDC

Tidal Forcing: ADCIRC

Open Boundary

slide51

Modeling Exchange Between

Biological Model Grids

DYE_01

DYE_02

DYE_03

DYE_06

DYE

04

DYE

05

DYE_07

DYE_09

DYE_08

slide55

Model-Data Comparison

Salinity - Phillipsdale

Model

Salinity (ppt)

Data

Time (days)

slide58

Goal: Understand chemistry, biology and physics

of the Bay, at all points in the Bay, for all time

slide59

Goal: Understand chemistry, biology and physics

of the Bay, at all points in the Bay, for all time

Goal 2: Understand coupled processes given any

combination of external forcing conditions

slide60

Numerical Model

Equations

Momentum balance x & y directions:

u + vu – fv = f + Fu + Du

t x

v + vv + fu = f + Fv + Dv

ty

Potential temperature and salinity :

T+ vT = FT + DT

t

S + vS = FS + DS

t

The equation of state:

r= r (T, S, P)

Vertical momentum:

f = - r g

z ro

Continuity equation:

u+v+w = 0

x y z

Initial Conditions

Forcing Conditions

ROMS Model

Regional Ocean

Modeling System

Output

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