VHF profiler observations of winds and waves in the troposphere during the Darwin Area Wave Experiment (DAWEX)

Abstract

A VHF atmospheric radar (wind profiler) was used to study tropospheric winds during the Darwin Area Wave Experiment (DAWEX). The profiler, which operated at a frequency of 54.1 MHz, was located at Pirlangimpi (Garden Point) (11.4°S, 130.5°E) on the Tiwi Islands. Observations were made regularly up to heights near 8 km, with maximum heights occurring when convective activity was strongest. Mean winds observed between October and December 2001 are in good agreement with conditions that prevailed across northern Australia during this period. During the first two intensive observation periods (IOP) during October and November, the zonal and meridional wind components were westward and northward, respectively, with stronger values in November. By the time of IOP3 in mid‐December, the zonal flow was eastward, a pattern that is typical of the Australian monsoon. Fluctuations in the three wind components for periods less than 3 hours are analyzed for IOP2 in November, when strong convective storms (“Hectors”) occurred on all afternoons over the Tiwi Islands. The fluctuations, which are ascribed to convectively generated gravity waves, show a correspondingly strong diurnal cycle, with horizontal wind variances peaking between 8 and 12 m2s−2 in the early afternoon in the lower troposphere. Variances are only ∼2 m2s−2 in the early morning hours. A power spectral analysis shows that oscillations with ground‐based periods between 8 and 17 min are especially prominent during Hector events. The profiler observations are compared with a numerical model study of gravity wave generation by convection on 17 November 2001. There is a satisfactory degree of agreement between the behavior of the model and profiler oscillations, both as a function of height and time.