THE AUSTRALIAN NOCTURNAL JET AND DIURNAL-VARIATIONS OF BOUNDARY-LAYER WINDS OVER MT-ISA IN NORTH-EASTERN AUSTRALIA

An analysis of radiosonde data shows the nocturnal boundary-layer jet over Australia to be continental in scale. The detailed temporal development of the jet is described using two years of boundary-layer wind-profiler data from Mt. Isa in north-eastern Australia. A distinct isallobaric wind is found, which has a spectral peak near the inertial period. This is associated with the diurnal pressure-oscillation and developments in the heat low over central and western Australia. However, it is not important for the development of the nocturnal jet. The nocturnal jet begins as a shallow disturbance and grows through the night. Most of the year the wind maximum is at about 500 m above the ground and has a well-defined jet-profile. In the summer-monsoon season the vertical extent of the wind maximum increases, but has weaker vertical shear. The jet results from an inertial response, but is affected by other processes. The amplitude of the jet is less than would be expected from a straightforward response to the daytime ageostrophic flow and there is super-inertial rotation and damping of the wind vector late in the night.