Application of ROMS for the Spencer Gulf

and on the adjacent shelf of South Australia

Carlos Teixeira & SARDI Oceanography Group

Aquatic Sciences

2009 ROMS/TOMS Asia-Pacific Workshop

Wintertime Outflow of Wintertime Outflow of Spencer GulfSpencer Gulf

Contours of near-bottom salinity (16-23 June 1986. Lennon et al. 1987)

During winter, the gulf waters are cooled and become denser than the shelf waters. This dense water flows out to the adjacent shelf.

Sea Surface Temperature from satellite measurements

Summertime OutflowSummertime Outflow

During summer, the gulf waters become denser due the evaporation, but the upwelled waters in the shelf block the gulf outflow.

SAIMOS

• To monitor and better understand the gulfs and shelf circulation, $6.5M invested in the Southern Australian Integrated Marine Observing System.

Planned Planned SAIMOS SAIMOS Infrastructure:Infrastructure:

Shelf/Slope Moorings

Reference Station

• Monthly CTD Stations for 2 years

HF Radar

PLUS

• Gliders

The data will be used to initialize, force and validate the hydrodynamic/bio-geochemical model for the region.

What modelling we intend to do?

• Idealized forcing to better understand the fundamental physics of the circulation within the Spencer Gulf (my PhD thesis)

• Hydrodynamic/ Biogeochemical model for the Spencer Gulf and adjacent shelf

Tides

• Barotropic Experiment

• OTPS / TP07.1 tidal forcing

• Free surface CHAPMAN BC

• 2D Momentum FLATHER BC

• Bottom Friction:– Linear– Quadratic– Logarithmic

Grid and Validation

Spencer Gulf

San Vincent

Gulf

• 3 x 3 Km grid• Amplitudes and Phases compared with Australian National Tide Tables

Amplitudes M2

West Coast

East Coast

San Vincent GulfSpencer Gulf

Phases M2

West Coast

East Coast

San Vincent GulfSpencer Gulf

Summary:• Best results with Quadratic Law scheme for Bottom friction. • Good agreement with ANTT in the stations outside the gulfs• Reasonable inside the Spencer Gulf • Poor inside San Vincente Gulf

Next Steps:• Nested model for gulfs using a high resolution grid

• Assimilation of SSH data inside the gulfs?

Local vs Remote wind?

Remote Wind =

Coastal Trapped Waves

Local

Wind

• 5 x 5 Km uniform grid• 20 Sigma levels • Analytical initial values for temperature and salinity

Same vertical profile everywhere (no horizontal gradient).

• Free surface CHAPMAN BC• 2D Momentum FLATHER BC• Gradient BC for 3D momentum and tracers• Tangent RADIATION_2D and Sponge area used in

the eastern boundary• Mellor and Yamada 2.5 turbulence closure method • 3rd-order upstream horizontal advection• 4th-order centered vertical advection

Remote wind

– Mode 1 CTW cross-shelf eigenfunction determined for the western boundary topography (Brink and Chapman,1985).

– Eigenfunction used to create SSH and external

velocities in the western boundary (Paddle).

Remote Wind – CTWResults

Paddle

Sea Level

Paddle

External Velocity

Local wind– 10 days oscillatory zonal and meridional

wind Stress (0.1 Pa)– Wind Stress tapered to the gulfs area

17.5 Days

Wind Stress

Local Wind – Cross ShoreResults

Sea Level

1

2

3

External Velocity

Diagnostics

4

7

9

COADS Wind Forcing

• Model forced with COADS monthly winds for 1 year;

• Passive Tracers used to study the connection between the Gulfs;

Summary from Wind Model• ROMS model with analytical initial conditions and

forcing was very valuable to better understand the circulation within Spencer Gulf

• Remote winds will be unimportant to the circulation within the gulfs;

• Local winds will generate a weak circulation in most

part of the gulf, with the exception of shallow areas;

• There is a strong transport from the SG to the SVG,

but not from SVG to the SG.

Next Steps….

• Use Met Stations and local atmospheric model data for better represent the wind stress inside the Gulfs and compare the results with SAIMOS data;

Summer Scenario:

• Initiate the model with realistic data and atmospheric forcing to try to reproduce summer scenario.

Thank you!