We analyze data from 17 high-resolution thermosonde observations during a campaign near Adelaide, Australia, in 1998. We are able to explain the observed turbulence fractions by extending the turbulence model of Hines <1991>, which explains turbulence by instabilities due to freely propagating independent gravity waves, from the hydrostatic wave regime toward lower frequencies. In a Monte Carlo simulation we show that the dependency of the observed gravity wave spectrum on vertical wave number is also consistent with the distribution of turbulent layer thickness as observed by the high-resolution thermosondes.