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Impact of Mascarene High variability on the East African ‘short rains’

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Abstract

The interannual variability of East African ‘short rains’ (EASR) and its link with the Mascarene High (MH) variation are explored, using observations and reanalysis data. Correlation and composite analyses for flood and drought events reveal that the EASR variability is strongly linked to the MH zonal displacement, in particular, the zonal movement of the MH eastern ridge. When the MH eastern ridge is anomalously displaced to the west (east) of its normal position, the south east (SE) trade winds over the South Indian Ocean (SIO) anomalously strengthen (weaken). This enhances (reduces) the relatively cool and dry SE trade winds and induces cold (warm) sea surface temperature anomaly in the SIO. As a result, convection over the western equatorial SIO is suppressed (enhanced) and leads to rainfall deficits (excess) over East Africa. Droughts in East Africa are associated with a westward migration of the MH eastern ridge, while the relationship is less clear for flood events and their link to an eastward migration of the MH. Therefore, the zonal migration of the MH eastern ridge provides a novel indicator for the EASR extremes especially droughts. This revelation has immense social application for rainfall forecast over East Africa where rainfall deficits have become more prevalent against the background of deteriorating conventional forecasts for EASR droughts.

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Acknowledgments

Material and financial support from JSPS and JAMSTEC for the writing and publication of this paper is greatly appreciated. University of Tokyo (Japan) and Bindura University of Science (Zimbabwe) is thanked for providing the enabling environment and facilities.

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Authors and Affiliations

  1. Department of Geography, Bindura University of Science, Bindura, Zimbabwe

    Desmond Manatsa & Caxston H. Matarira

  2. Department of Ocean Technology, Policy, and Environment, University of Tokyo, Tokyo, Japan

    Desmond Manatsa & Swadhin K. Behera

  3. Research Institute for Global Change, JAMSTEC, Yokohama, Japan

    Desmond Manatsa, Yushi Morioka, Swadhin K. Behera & Toshio Yamagata

  4. International Center for Theoretical Physics (ICTP), 34151, Trieste, Italy

    Desmond Manatsa

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  1. Desmond Manatsa
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  2. Yushi Morioka
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  3. Swadhin K. Behera
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  4. Caxston H. Matarira
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  5. Toshio Yamagata
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Correspondence to Desmond Manatsa.

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Manatsa, D., Morioka, Y., Behera, S.K. et al. Impact of Mascarene High variability on the East African ‘short rains’. Clim Dyn 42, 1259–1274 (2014). https://doi.org/10.1007/s00382-013-1848-z

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  • DOI: https://doi.org/10.1007/s00382-013-1848-z

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