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Climate variability over the Greater Horn of Africa based on NCAR AGCM ensemble

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Summary

The variability and extreme wet anomalies in the Greater Horn of Africa (GHA) climate are investigated based on a multi-year National Center for Atmospheric Research (NCAR) AGCM ensemble data. While the GCM ensemble average reproduces realistic inter-annual variability of rainfall pattern over the GHA sub-region compared to observations, there is a distinct northward shift in the simulated regions of rainfall maxima throughout the season. However, in agreement with observations and many previous studies, the inter-annual variability derived from leading mode of EOF analysis is dominated by ENSO-related fluctuations. On the other hand, the spatial pattern corresponding to the second mode (EOF2) exhibits a unique dipole rainfall anomaly pattern (wet/dry conditions) over the northern/southern halves of our domain during all the three months of the short rains season. When the 3–10 year periodicity is filtered out from the 40-year EOF2 time series of the ensemble mean data, three distinct quasi-decadal regimes in the rainfall anomalies is exhibited for both monthly and seasonal mean data.

It is also evident from our results that a combination of anomalous surface and mid-tropospheric flow from northwestern and eastern Atlantic Ocean and easterly flow from the Indian Ocean played a significant role in setting up the non-ENSO related 1961 floods. Coversely, during the ENSO-related 1997 floods, the mid-troposheric flow was characterized by anomalous westerly flow originating from the Congo rainforest that converged with the flow from Indian Ocean along the East Africa coast and over eastern/northeastern Kenya. The anomalous moisture flux convergence/divergence in both the ensemble and NCEP reanalysis is also consistent with the mid-trospheric flow anomalies that are associated with the two wet events.

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  1. Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina, USA

    R. O. Anyah & F. H. M. Semazzi

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  1. R. O. Anyah
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  2. F. H. M. Semazzi
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Anyah, R., Semazzi, F. Climate variability over the Greater Horn of Africa based on NCAR AGCM ensemble. Theor. Appl. Climatol. 86, 39–62 (2006). https://doi.org/10.1007/s00704-005-0203-7

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  • DOI: https://doi.org/10.1007/s00704-005-0203-7

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