Mountain wave turbulence in the lee of the Hex River Mountains

[摘要] ENGLISH ABSTRACT: Despite recorded mountain wave related aircraft accidents in South Africa, verylittle literature exists on South African mountain waves. This study discusses theresults of a mountain wave study in the Hex River Mountains in the Western Capeprovince of South Africa. The aim of this study was to measure mountain waveturbulence on the lee side of the mountains by conducting weather balloonsoundings on the upwind and lee sides of the mountains. These soundings wereperformed over four days in the winter and spring, with each field day representingdifferent synoptic scale weather conditions. Lee wave rotors were detected fromseveral of the lee wave soundings. Significant values of horizontal vorticityaround a north-south axis (y-component horizontal vorticity) were detected. Theinstrumentation was highly sensitive and able to measure even weak up anddowndraft velocities associated with the rotors. Strong downdrafts were measuredsome mountain waves, but no strong downdrafts were detected near rotors whichoccurred below the mountain waves. The two dimensional positions of balloonswere only available after a considerable amount of reanalysis. If this data can bemade available onsite shortly after soundings, it can be used to decide where tomove launch sites to, in order to obtain optimal results.

[发布机构] Stellenbosch University