Climate variability over the Greater Horn of Africa based on NCAR AGCM ensemble |
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Authors: | R O Anyah F H M Semazzi |
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Institution: | (1) Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina, USA |
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Abstract: | 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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