Abstract
The impacts of the low level jets that form through the gaps in the topography in the Limpopo and Zambezi River Valleys (LRV and ZRV) on southern African climate are investigated. ERA-5 reanalysis data and numerical experiments using regional climate models reveal that the two valleys act as main gateways for southwest Indian Ocean-sourced moisture inflows into southern Africa. The effects of the LRV jet are stationary and mostly confined to south of Limpopo. By blocking the LRV, the moisture convergence in the interior of the subcontinent reduces and leads to a weakening in both the Angola Low and the ridging high over southeastern Africa. These are unfavorable conditions for the southward transport of moisture, causing a decrease of up to 50% of the subtropical southern African total summer rainfall. In contrast, the influence of the Zambezi jet varies with the season. During early austral summer, a blocked ZRV results in an overall deficit in rainfall in the subcontinent. It then leads to a weaker Mozambique Channel Trough, intensified Angola Low, hence increase in rainfall during January and February. Toward the end of the austral summer season, the absence of the Zambezi jet allows more moisture from the tropical Atlantic to penetrate into the mainland which then converges with moisture transported from the Indian Ocean and triggers excess rainfall over the tropical areas. These results have important implications for understanding the intraseasonal and interannual rainfall variability over the subcontinent during the summer half of the year.
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Acknowledgements
We would like to thank the two anonymous reviewers for their constructive comments that substantially contribute to the improvement of the manuscript.
Funding
This work was supported through the Climate Research for Development (CR4D) Postdoctoral Fellowship CR4D-19-13 implemented by the African Academy of Sciences (AAS) in partnership with the United Kingdom’s Department for International Development (DfID) Weather and Climate Information Services for Africa (WISER) program and the African Climate Policy Center (ACPC) of the United Nations Economic Commission for Africa (UNECA).
It is also supported by NERC (Natural Environment Research Council), as part of the UMFULA project (NE/M020223/1) funded by the FCFA (Future Climate For Africa) program. Support for this study has been provided by the University of Cape Town as well. All the simulations have been run on the national UK Cluster ARCHER with a financial support provided by the UMFULA project.
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Barimalala, R., Blamey, R.C., Desbiolles, F. et al. The influence of southeastern African river valley jets on regional rainfall. Clim Dyn 57, 2905–2920 (2021). https://doi.org/10.1007/s00382-021-05846-1
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DOI: https://doi.org/10.1007/s00382-021-05846-1