Evaporative dense water formation and cross-shelf exchange over the northwest Australian inner shelf

Abstract

High-resolution surveys of oceanographic and atmospheric conditions made during the winter over the inner shelf off northwest Australia are used to examine the coastal ocean response to large outgoing heat and freshwater fluxes. Relatively cool, low-humidity air blows off the Australian continent out over the tropical continental shelf, resulting in a large mean latent heat flux (−177 W m−2) that overwhelms insolation and, along with the outgoing long-wave radiation, results in substantial net cooling (−105 W m−2) and evaporative freshwater flux (0.6 cm d−1). The inner shelf is characterized by increasingly cool, salty, and dense waters onshore, with a strong front near the 25 m isobath. The front is evident in satellite sea surface temperature (SST) imagery along the majority of the northwest Australian shelf, exhibiting a complex filamentary and eddy structure. Cross-shelf buoyancy fluxes estimated from the mean, two-dimensional heat and salt budgets are comparable to parameterizations of cross-shelf eddy driven fluxes; however, the same fluxes can be achieved by cross-shelf transports in the bottom boundary layer of about 0.5 m2 s−1 (and an overlying return flow).