Nocturnal low-level turbulence near Cambridge Aerodrome

Two incidents in the early night hours are outlined which involved aircraft immediately after take-off from the aerodrome at Cambridge, Tasmania Certain features in both incidents suggest that horizontal rather than vertical currents were responsible. The complete meteorological information available for one of the incidents suggests the presence of lee waves; these appear however to have been restricted to higher levels. Evidence for horizontal currents is found in the surface wind records, which in both cases show marked long-period surges. These are attributed in one case to quasi-stationary eddies behind the hills west of the aerodrome, and in the other to stagnation of cold surface air, favoured by the topography of the region. The latter process seems to be accompanied at times by the formation of large eddies with vertical axes. Both incidents (as well as at least one earlier crash) occurred during temporary lulls in the wind. It is suggested that the difficulties were caused essentially by the large wind gradients in the zone of transition above and around the stagnant or slower-moving surface air.