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 Spencer Gulf Contours of near-bottom salinity (16-23 June 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 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 SAIMOS 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 Gulf Spencer Gulf

Phases M2 West Coast East Coast San Vincent Gulf Spencer 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 3 rd -order upstream horizontal advection 4 th -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 – CTW Results 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 Shore Results 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!