Modelling meso-scale dynamics along western and southern Australian shelf and slopes: A ROMS modelling approach

As part of a study on “ocean-shelf exchange with an emphasis on the roles of waves, tides, eddies and cross-shelf flows on carbon exchange”, funded through ANNIMS, a three-dimensional (3D) model was configured to include the western and southern Australian shelves, slopes and the adjacent deep ocean using ROMS. The model domain, extending from the Kimberley to Bass Strait, uses curvilinear-orthogonal grids with 2-4 km horizontal resolution for the entire region with 1-2 km resolution in the sub-domains (north-west, central-west and south-west) with 30 sigma layers in the vertical water column. The model was forced with daily atmospheric (wind and air pressure) and air sea fluxes (heat and freshwater). The model open boundaries were specified with monthly salinity and temperature climatology. The model forcing included tides and monthly mean sea levels. The model initial and forcing data (2000-2010) were extracted from various global and Australian oceanographic/meteorological data sources and interpolated in to surface horizontal mesh and open boundary vertical sections.

In this presentation, we highlight the major physical processes in the region using ROMS model output. The model is able to reproduce the tidal characteristics, major surface and sub-surface currents systems (e.g. Leeuwin Current, Leeuwin Undercurrent, Capes current etc.), and associated eddy fields. The model also reproduced the seasonal processes such as: summer upwelling along Ningaloo and the Capes region, dense water formation and cascading in the central western Australian shelf. The model predicted surface currents were compared with HF radar data (Perth region) and cross-shelf flows with current meter moorings. Model predicted SST and SSH was compared to satellite measurements.

We have also examined the contribution from different forcing agents on physical processes in the region by including and excluding different model forcing terms or assigning a forcing variable to a constant value or zero. We found that the distribution of atmospheric pressure (in addition to other forcing agents) also significantly influences the strength of southward flowing currents (e.g. Leeuwin current). Currently we are in the process of coupling the physical and biogeochemical ROMS model to study the influence of these different processes on the shelf carbon exchange process.

E.M.S. Wijeratne1, Charitha Pattiaratchi1 and Roger Proctor2,
1School of Environmental Systems Engineering and UWA Oceans Institute, The University of Western Australia,
2University of Tasmania, Hobart TAS 7001