Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Despite recorded mountain wave related aircraft accidents in South Africa, very
little literature exists on South African mountain waves. This study discusses the
results of a mountain wave study in the Hex River Mountains in the Western Cape
province of South Africa. The aim of this study was to measure mountain wave
turbulence on the lee side of the mountains by conducting weather balloon
soundings on the upwind and lee sides of the mountains. These soundings were
performed over four days in the winter and spring, with each field day representing
different synoptic scale weather conditions. Lee wave rotors were detected from
several of the lee wave soundings. Significant values of horizontal vorticity
around a north-south axis (y-component horizontal vorticity) were detected. The
instrumentation was highly sensitive and able to measure even weak up and
downdraft velocities associated with the rotors. Strong downdrafts were measured
some mountain waves, but no strong downdrafts were detected near rotors which
occurred below the mountain waves. The two dimensional positions of balloons
were only available after a considerable amount of reanalysis. If this data can be
made available onsite shortly after soundings, it can be used to decide where to
move launch sites to, in order to obtain optimal results. / AFRIKAANSE OPSOMMING: Ten spyte van gedokumenteerde berggolf-verwante vliegongelukke, bestaan baie
min literatuur oor Suid Afrikaanse berggolwe. Hierdie tesis bespreek die resultate
van ‘n berggolfstudie in die Hexrivier Berge in the Weskaap Provinsie van Suid-
Afrika. Die doel van hierdie studie was om die berggolfturbulensie aan die lykant
van die berge te meet deur middel van weerballonopstygings aan beide die winden
lykante van die berge. Hierdie opstygings is oor ‘n tydperk van vier winter en
lente dae uitgevoer, met elkeen van die dae wat verskillende sinoptiese
weersomstandighede verteenwoordig het. Rotors is waargeneem in die data van
verskeie ballonopstygings wat aan die lykant uitgevoer is. Beduidende waardes
van horisontale vortisiteit rondom ‘n noord-suid as (y-komponent horisontale
vortisiteit) is gemeet. Die instrumentasie was hoogs sensitief en kon selfs swak
op- en afstrominge meet. Sterk afstrominge is waargeneem in berggolwe, maar nie
in die omgewing van rotors wat onmder die berggolwe voorgekom het nie. Die
twee-dimensionele posisies van ballonne was slegs na aansienlike heranaliese van
die data beskikbaar. Indien hierdie data kort na opstygings beskikbaar is tydens
veldwerk, kan dit help met besluite oor alternatiewe posisies waarvandaan
ballonopstygings gedoen kan word ten einde optimale resultate te bekom.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/20240 |
| Date | 03 1900 |
| Creators | Van Der Mescht, Deon |
| Contributors | Eloff, P. J., Stellenbosch University. Faculty of Arts and Social Sciences. Dept. of Geography and Environmental Studies. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 150 p. : ill., maps |
| Rights | Stellenbosch University |
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