@article{HoehnFrimmelDebailleetal.2021,
  author    = {H{\"o}hn, Stefan and Frimmel, Hartwig E. and Debaille, Vinciane and Price, Westley},
  title     = {Pre-Klondikean oxidation prepared the ground for Broken Hill-type mineralization in South Africa},
  series = {Terra Nova},
  volume    = {33},
  journal   = {Terra Nova},
  number    = {2},
  doi       = {10.1111/ter.12502},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-218545},
  pages     = {168 -- 173},
  year      = {2021},
  abstract  = {New Cu isotope data obtained on chalcopyrite from the Black Mountain and the Broken Hill deposits in the medium- to high-grade metamorphic Aggeneys-Gamsberg ore district (South Africa) require a revision of our understanding of the genesis of metamorphic Broken Hill-type massive sulphide deposits. Chalcopyrite from both deposits revealed unusually wide ranges in δ\(^{65}\)Cu (-2.41 to 2.84 per mille NIST 976 standard) in combination with distinctly positive mean values (0.27 and 0.94 per mille, respectively). This is interpreted to reflect derivation from various silicate and oxide precursor minerals in which Cu occurred in higher oxidation states. Together with the observation of a typical supergene base metal distribution within the deposits and their spatial association with an unconformity only meters above the ore horizon, our new data are best explained by supergene oxidation of originally possibly SEDEX deposits prior to metamorphic sulphide formation, between the Okiepian (1,210-1,180 Ma) and Klondikean (1,040-1,020 Ma) orogenic events.},
  language  = {en}
}
@article{Ibebuchi2021,
  author    = {Ibebuchi, Chibuike Chiedozie},
  title     = {Revisiting the 1992 severe drought episode in South Africa: the role of El Ni{\~n}o in the anomalies of atmospheric circulation types in Africa south of the equator},
  series = {Theoretical and Applied Climatology},
  volume    = {146},
  journal   = {Theoretical and Applied Climatology},
  number    = {1-2},
  issn      = {1434-4483},
  doi       = {10.1007/s00704-021-03741-7},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-268569},
  pages     = {723-740},
  year      = {2021},
  abstract  = {During strong El Ni{\~n}o events, below-average rainfall is expected in large parts of southern Africa. The 1992 El Ni{\~n}o season was associated with one of the worst drought episodes in large parts of South Africa. Using reanalysis data set from NCEP-NCAR, this study examined circulation types (CTs) in Africa south of the equator that are statistically related to the El Ni{\~n}o signal in the southwest Indian Ocean and the implication of this relationship during the 1992 drought episode in South Africa. A statistically significant correlation was found between the above-average Nino 3.4 index and a CT that features widespread cyclonic activity in the tropical southwest Indian Ocean, coupled with a weaker state of the south Indian Ocean high-pressure. During the analysis period, it was found that the El Ni{\~n}o signal enhanced the amplitude of the aforementioned CT. The impacts of the El Ni{\~n}o signal on CTs in southern Africa, which could have contributed to the 1992 severe drought episode in South Africa, were reflected in (i) robust decrease in the frequency of occurrence of the austral summer climatology pattern of atmospheric circulation that favors southeasterly moisture fluxes, advected by the South Indian Ocean high-pressure; (ii) modulation of easterly moisture fluxes, advected by the South Atlantic Ocean high-pressure, ridging south of South Africa; (iii) and enhancement of the amplitude of CTs that both enhances subsidence over South Africa, and associated with the dominance of westerlies across the Agulhas current. Under the ssp585 scenario, the analyzed climate models suggested that the impact of radiative heating on the CT significantly related to El Ni{\~n}o might result in an anomalous increase in surface pressure at the eastern parts of South Africa.},
  language  = {en}
}
@article{Ibebuchi2021,
  author    = {Ibebuchi, Chibuike Chiedozie},
  title     = {Circulation pattern controls of wet days and dry days in Free State, South Africa},
  series = {Meteorology and Atmospheric Physics},
  volume    = {133},
  journal   = {Meteorology and Atmospheric Physics},
  number    = {5},
  issn      = {1436-5065},
  doi       = {10.1007/s00703-021-00822-0},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-268552},
  pages     = {1469-1480},
  year      = {2021},
  abstract  = {Atmospheric circulation is a vital process in the transport of heat, moisture, and pollutants around the globe. The variability of rainfall depends to some extent on the atmospheric circulation. This paper investigates synoptic situations in southern Africa that can be associated with wet days and dry days in Free State, South Africa, in addition to the underlying dynamics. Principal component analysis was applied to the T-mode matrix (variable is time series and observation is grid points at which the field was observed) of daily mean sea level pressure field from 1979 to 2018 in classifying the circulation patterns in southern Africa. 18 circulation types (CTs) were classified in the study region. From the linkage of the CTs to the observed rainfall data, from 11 stations in Free State, it was found that dominant austral winter and late austral autumn CTs have a higher probability of being associated with dry days in Free State. Dominant austral summer and late austral spring CTs were found to have a higher probability of being associated with wet days in Free State. Cyclonic/anti-cyclonic activity over the southwest Indian Ocean, explained to a good extent, the inter-seasonal variability of rainfall in Free State. The synoptic state associated with a stronger anti-cyclonic circulation at the western branch of the South Indian Ocean high-pressure, during austral summer, leading to enhanced low-level moisture transport by southeast winds was found to have the highest probability of being associated with above-average rainfall in most regions in Free State. On the other hand, the synoptic state associated with enhanced transport of cold dry air, by the extratropical westerlies, was found to have the highest probability of being associated with (winter) dryness in Free State.},
  language  = {en}
}