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Africánes in southern Africa: attributes and contribution to rainfall of a continental tropical low

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Abstract

Large parts of southern Africa are influenced by extra-tropical weather systems for most of the year. During late summer (December–March), the circulation over the area becomes distinctly tropical. This paper introduces the Africáne, a synoptic scale tropical low-pressure system which has been shown to cause widespread and heavy rainfall over the southern sub-continent of Africa. The frequency of occurrence of Africánes, their contribution to rainfall and interannual variability are discussed in this paper. Africánes occur most frequently at the longitude of the Caprivi area with a second peak in frequency at around 32.5° E. They mostly occur over Namibia, Botswana and Zimbabwe and only infrequently infiltrate as far south as the borders of South Africa. However, when they do occur over South Africa, they cause widespread heavy rainfall and floods. Rainfall is mostly confined to the eastern flank of Africánes and between 20 and 35% of the annual rainfall over southern Africa in late summer can be attributed to these systems. There are two main synoptic regimes associated with Africánes: a westerly wave or tropical-temperature trough combines with the Africáne to pull rainfall southwards into South Africa. The second, is a mid-level subtropical high pressure, located south of the Africáne, which causes the rainfall to be confined to the north. The interannual variability of Africánes are closely linked to rainfall over southern Africa, such that an above normal number of Africánes in a season causes above normal rainfall over southern Africa. The number of Africánes that form per year is linked to El Niño–Southern Oscillation (ENSO). It is recommended that the predictability of Africánes on different time scales should be investigated.

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All data used in the paper are public good data. All output data are available on request.

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Available on request.

Notes

  1. http://www.bom.gov.au/cyclone/tropical-cyclone-knowledge-centre/history/tracks/.

  2. https://climatedataguide.ucar.edu/climate-data/ibtracs-tropical-cyclone-best-track-data.

  3. http://www.meteo.fr/temps/domtom/La_Reunion/webcmrs9.0/anglais/index.html.

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Acknowledgements

The authors would like to thank the South African Water Research Commission who funded the research into continental tropical lows in southern Africa.

Funding

The MSc study of Elizabeth Viljoen (nee Webster) was funded by the South African Water Research Commission [Grant no. K5-2510].

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Authors and Affiliations

  1. South African Weather Service, Pretoria, South Africa

    Elizabeth Viljoen & Ishmael Moyo

  2. Department of Geography, Geoinformatics and Meteorology, University of Pretoria, Pretoria, South Africa

    Elizabeth Viljoen, Liesl Dyson & Ishmael Moyo

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  1. Elizabeth Viljoen
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Contributions

EV (née Webster) conducted a significant amount of the research as part of her MSc qualification. LD, supervised the MSc study, conducted part of the research and edited the manuscript. IM contributed to the general circulation and dynamics investigation as part of on-going research.

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Correspondence to Liesl Dyson.

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Viljoen, E., Dyson, L. & Moyo, I. Africánes in southern Africa: attributes and contribution to rainfall of a continental tropical low. Clim Dyn 60, 1599–1617 (2023). https://doi.org/10.1007/s00382-022-06380-4

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