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African Easterly Jet South: control, maintenance mechanisms and link with Southern subtropical waves

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Abstract

The African Easterly Jet South (AEJ-S) is an important feature of the central African mid tropospheric circulation and has been identified as a key contributor to convection over the region. This study uses 21-year (1983–2003) Reanalysis data sets of ERA-Interim, NCEP2 and MERRA2 to establish mechanisms related to AEJ-S dynamics. Results demonstrate that AEJ-S is dominated by rotational circulation and is maintained by a mid-level high that forms over the Kalahari region during September to November. Because of the role played by this high pressure system in the AEJ-S dynamics, an effort is made to understand how this anticyclone develops. We show that this mid-tropospheric high over the Kalahari region is established in response to lower tropospheric dry convection over the region from September to November. At the core of this high, anticyclonic circulation is induced and maintains AEJ-S located at the northern flank of the high. A link between AEJ-S dynamics and southern subtropical westerly waves is also revealed. It is shown that, when waves amplify over the southern subtropics, they modify lower tropospheric heating. Depending on the phase of the wave, this modifies the cross latitude temperature gradient throughout equatorial regions, therefore modulating the intensity of the jet. By clarifying the mechanisms that govern the AEJ-S, this research work contributes to insight into central Africa climate mechanisms and also suggests a link between central Africa and Southern Africa climate systems. This research work also improves the foundation of new mechanisms that help to identify suitable metrics for the evaluation of Global models over the Central Africa region.

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Acknowledgements

The authors are partly supported by the NERC-funded IMPALA (NE/M017206/1) and UMFULA (NE/M020207/1) programs. The authors acknowledge the helpful inputs of Pierre Honore KAMSU, Vondou Derbetini, Neil Hart, Rachel James, Emma Howard and Thierry Taguela, and thank the two reviewers for their constructive comments on the manuscript. We also acknowledge all the reanalysis data provider used in this study.

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Authors and Affiliations

  1. Laboratory for Environmental Modelling and Atmospheric Physics (LEMAP), University of Yaounde 1, Yaounde, Cameroon

    Giresse Kuete & Wilfried Pokam Mba

  2. School of Geography and the Environment, University of Oxford, Oxford, UK

    Richard Washington

  3. Department of Physics, Higher Teacher Training College, University of Yaounde 1, Yaounde, Cameroon

    Wilfried Pokam Mba

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  1. Giresse Kuete
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  2. Wilfried Pokam Mba
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Correspondence to Giresse Kuete.

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Kuete, G., Pokam Mba, W. & Washington, R. African Easterly Jet South: control, maintenance mechanisms and link with Southern subtropical waves. Clim Dyn 54, 1539–1552 (2020). https://doi.org/10.1007/s00382-019-05072-w

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  • DOI: https://doi.org/10.1007/s00382-019-05072-w

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