WAMSI Node 1.1.1 - Downscaled hydrodynamic models

This work describes the physical oceanography at successively smaller scales, from that of the eastern Indian Ocean, to the shelf from NW Cape to Cape Leeuwin, down to the Marmion lagoon. At the largest scale, the primary tool is the global Ocean Forecasting Australia Model (OFAM), that has coarse (>2 degree) resolution distant from Australia, but has 0.1 degree (~10 km) resolution in the Australasian region. Being global, OFAM simulates the longshore pressure gradient, largely due to the Indonesian Throughflow, that drives the Leeuwin Current southward along the shelf break of the WA coast. The model provides good qualitative representation of the Leeuwin Current and its associated eddies but, at 10 km resolution, tends to underestimate the current speeds on the shelf and cross-shore fluxes.\n\nOFAM output has been corrected with observations (in a separate CSIRO project) and archived to provide nearly 2 decades of ocean conditions. As a prelude to later biological investigations, it is used to investigate the longshore connectivity of shelf waters, demonstrating that the shelf can be classified into several sections of alternating low and high retention. At this scale, openocean swells are important, with biological particles near the surface being driven north-east under their influence.\n\nAt the next level, the Rutgers Ocean Modelling System (ROMS) is nested inside OFAM, covering the southern west shelf, with resolution down to 2 km near the coast. ROMS produces similar patterns of circulation to OFAM, but the Leeuwin Current and inshore wind-driven currents are narrower and stronger. The ROMS model is used primarily to drive a model of primary productivity over the shelf. ROMS produces eddies that correspond well with those observed in sea-surface temperature images, and also shows instances of intermittent upwelling along the shelf break. Upwelling and eddy transport prove to be significant mechanisms for moving nutrients and phytoplankton on and off the shelf, respectively. \n\nAt the scale of the Marmion lagoon, surface waves breaking on the reefs drive currents in the lagoon. The present study incorporated a year-long measurement program to quantify the reef and lagoon circulation. At low wave heights, the lagoonal circulation is driven primarily by longshore winds. However, when the incoming waves are higher than about 1.5 m, they break on the reef, carrying water into the lagoon, and causing currents to the north and south out of the lagoon. Modelling of reef dynamics requires very high resolution, down to tens of metres, and a model that includes both waves and currents. Two model configurations have been used in the present study: ROMS together with the wave model SWAN, and Xbeach, a littoral-zone model still under development at Delft University. Xbeach accurately represents the lagoonal dynamics.\n\nAdditional information for this dataset may be available via the original MarLIN metadata entry:\nhttps://marlin.csiro.au/geonetwork/srv/eng/catalog.search#/metadata/2f636dcd-49a2-4359-9157-b52086e2027a\nLineage: Ocean Scale models:\nFor WAMSI modelling, the primary source of large-scale information is the global ocean model, OFAM (Ocean Forecasting Australia Model). OFAM has been run to create a 1993-2008 archive of daily values of ocean properties including ocean currents, salinity\nand temperature in the Australian region. There are two versions of the archive: one is a free run, and the second utilises data assimilation. \nA second source of global model data, is HYCOM, the Hybrid Coordinate Ocean Model, with a vertical coordinate that is isopycnal. The HYCOM hindcast system is configured for the global ocean with HYCOM 2.2 as the dynamical model. Computations are carried out on a Mercator grid between 78°S and 47°N (1/12° equatorial resolution). \n\nContinental Shelf Scale Models:\nA coupled hydrodynamic-biogeochemical model (ROMS) has been configured for the southwest shelf off Western Australia. \nResolution varies from 3 km to 8 km. There are 30 vertical levels with refinement in the top 200m. The model was integrated for 4 years from January 2000 to December 2003 and the solution for\n2003 is selected to represent the typical conditions of the Leeuwin Current System in the study region.\n\nLagoon Scale Models:\nBetween July 2007 and May 2008 in situ measurements of waves, currents and water properties were made on and around a series of reefs off Perth, Western Australia. The field site is characterised by a series of shallow limestone reefs about 3km offshore, the depth over the top of the reefs varies between 1 to 4m.\nThe field program consisted of in situ measurements of waves, currents and water properties at 11 sites using a variety of point current meters and profiling ADCPs, wave gauges and multi-sensors measuring temperature, salinity, oxygen, Photosynthetically\nActive Radiation (PAR), and fluorescence.