Summary
The mean monthly and annual rainfall series (1930–1977) for 30×30 blocks in the eastern Transvaal-Swaziland region ara analyzed. These series show temporal and spatial characteristics in the regional precipitation regime. Significance is attributed to oscillatory forcings with quasi-periodicities of about 16–20 years and 13–14 months that operate throughout the area. Oscillations near the quasi-biennial cycle are also observed but with less significance.
Principal component analysis provides a number of eigenvectors which are identified with changes in the seasonal characteristics of the regional rainfall. The annual cycle clearly dominates over the entire region with January (mid-summer) being the wettest month. The second eigenvector has pronounced loadings in the spring/early summer (November) period and clear spatial responses that are attributed to topographically induced differences in the deep convective processes of the area. Higher principal components are not as clearly defined in their temporal structure. The third eigenvector, however, is attributed partially to synoptic scale forcings which produce different rainfall characteristics over the coastal plains relative to the high inland plateau.
Zusammenfassung
Die mittleren monatlichen und jährlichen Regenfallsreihen (1930–1977) für ein 30×30 Bogenminuten-Netz im östlichen Transvaal und Swaziland wurden analysiert. Diese Reihen zeigen eine charakteristische zeitliche und räumliche Veränderlichkeit des Niederschlagsregimes, deren Signifikanz auf quasi-periodische Anregung mit Perioden von ungefähr 16–20 Jahren und 13–14 Monaten, im gesamten Gebiet evident, zurückgeführt werden kann. Schwingungen im Bereich eines quasi-biennalen Zykluses wurden ebenfalls beobachtet, jedoch mit geringerer Signifikanz.
Eine Analyse der Hauptkomponenten ergibt eine Anzahl von Eigenvektoren, welche mit den Änderungen im jahreszeitlichen Charakter des regionalen Niederschlages identifiziert werden können. Der Jahresgang dominiert eindeutig in der gesamten Region, wobei Januar (Mittsommer) der nasseste Monat ist. Der zweite Eigenvektor besitzt hohe Amplituden im Frühling und Frühsommer (November) und zeigt eine räumliche Verteilung, die auf topographisch induzierte Unterschiede in den Konvektionsprozessen dieses Gebietes zurückzuführen ist. Die Hauptkomponenten höherer Ordnung sind in ihrer zeitlichen Struktur nicht eindeutig definiert. Der dritte Eigenvektor kann jedoch zum Teil auf synoptische Vorgänge bezogen werden, welche in den Küstenebenen und im Plateau des Hinterlandes verschiedene Niederschlagsvertefungen bewirken.
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Kelbe, B.E., Garstang, M. & Brier, G. Analysis of rainfall variability in the northeastern region of South Africa. Arch. Met. Geoph. Biocl., Ser. B 32, 231–252 (1983). https://doi.org/10.1007/BF02273976
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DOI: https://doi.org/10.1007/BF02273976