The Leeuwin Current in the Parallel Ocean Climate Model and applications to regional meteorology and fisheries

Abstract

Unlike other currents along the subtropical west coasts of continents, the Leeuwin Current off Western Australia transports warm, fresh tropical waters poleward and is strong enough to overwhelm the upwelling tendencies of the coastal wind stress. The representation of this unusual and important current in the global eddy‐permitting ¼° Parallel Ocean Climate Model (POCM) is examined, and implications for coastal fisheries and regional weather and climate discussed. Comparison of POCM fields with those from the Leeuwin Current Interdisciplinary Experiment for austral autumn and winter 1987 suggests that model Leeuwin Current is consistent with these observations in terms of its location and depth distribution, surface gradients and meridional variation in mixed layer depths but is a bit weaker, warmer and fresher. The model Leeuwin Undercurrent is similar in strength to that observed during autumn/winter 1987. Similar to satellite observations, the model Leeuwin Current displays a number of meander, eddy and offshoot features. The frequency distribution and length scales of the model features are generally consistent with estimates of these parameters derived from the satellite images. It is concluded that POCM output can be usefully applied to improve understanding of the Leeuwin Current and associated regional impacts. Copyright © 1999 Royal Meteorological Society

Glacial Indonesian Throughflow weakening across the Mid-Pleistocene Climatic Transition

“…The ITF and its extension the LC are key in maintaining the relatively high coastal rainfall of Western Australia, creating a characteristic climate regime that has no counterpart to the hyper-arid coastal deserts found at similar latitudes in western South America and southern Africa 30 . In fact, model studies show that changes in the ITF can influence the rainfall of the entire Australian continent 34 .…”

“…The current is driven by a steric height gradient, which pushes warm fresh water coming through the ITF down the west coast of Australia 26 . The temperature of the LC responds to changes in the strength and direction of the ITF 27–29 , and plays an important role in modulating the hydrology of western Australia 30 .

Figure 1Overview map of oceanic circulation in the ITF region and its links to the Agulhas Current. Note the main path of the ITF through the Timor Strait feeding the Leeuwin Current (LC).

…”

Seasonal and interannual variations of upper ocean heat balance off the west coast of Australia

“…The model also captures the Leeuwin Undercurrent at 250–800 m depth, with an average northward transport of 2.9 Sv between 110°E and the coast (not shown). The sea surface kinetic energy in the Leeuwin Current region is also lower in ORCA025 compared with that derived from satellite altimeter data (Figure 4 (left)) [ Reason et al , 1999; Feng et al , 2005], but ORCA025 tends to capture the spatial distribution of the high eddy kinetic energy (Figure 4). The underestimate of the eddy energy is on one hand is because of the model resolution, and on the other hand is because of the fact that only the monthly averaged data are used for the calculation.…”

The behaviour of the Leeuwin Current offshore NW Australia during the last five glacial–interglacial cycles

“…Generally, the flow of the Leeuwin Current is strong enough to overwhelm the upwelling tendencies of the coastal wind stress; therefore, upwelling via Ekman transport does not occur offshore Western Australia (Reason et al 1999). However, due to seasonal differences in equatorward wind stress along the west coast of Western Australia, the Leeuwin Current flow is weaker between October and March (Pearce and Pattiaratchi, 1999;Meyers, 1996;England and Huang, 2005).…”