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John G. Dwyer, Michela Biasutti, and Adam H. Sobel

( Fu and Wang 2004 ; Kitoh and Arakawa 1999 ). Despite this, given the observed SST and radiative forcings, AGCMs capture the annual precipitation anomalies over land and for the tropics overall, although there is some discrepancy over ocean ( Liu et al. 2012 ). Similar studies where the annual cycle of SST was modified or suppressed have been carried out to study the effect of SST on the Asian summer monsoon ( Shukla and Fennessy 1994 ), the equatorial Atlantic and Pacific ( Li and Philander 1997

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Kerry H. Cook and Edward K. Vizy

1. Introduction Precipitation distributions over tropical East Africa exhibit pronounced regional variations, and the seasonal cycle is complicated. In most regions there are two peak rainfall seasons that are nominally associated with solar-heating maxima in the equinox seasons, but topography, SST forcing, and teleconnections to the West African and Indian monsoon systems are among the other important factors influencing the timing and intensity of seasonal rainfall. The tropical East African

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Lisa Hannak, Peter Knippertz, Andreas H. Fink, Anke Kniffka, and Gregor Pante

; Paxian et al. 2016 ). Moreover, Marsham et al. (2013) and Birch et al. (2014) show that issues in the diurnal cycle of latent heating and cloud radiative forcing impact on the north–south pressure gradient and thus the northward advection of moisture from the south to the Sahel. One element of the WAM that has received relatively little attention so far is the extensive cover of low- and midlevel clouds over southern West Africa (SWA) during the peak summer monsoon from July to September (JAS

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Elinor R. Martin and Chris Thorncroft

AEW forcing; maintenance, including representation of the AEJ; and feedbacks with convection in the atmospheric component of the models. While Fig. 2 shows the biases in the multimodel ensemble mean, it is important to assess the spread of the models’ ability to simulate AEWs. This is illustrated by Taylor diagrams of the spatial distribution of JJAS EKE at 700 and 850 hPa over West Africa and the eastern Atlantic (dashed box in Fig. 1b ) in Fig. 3 . The reference dataset used is the

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M. Issa Lélé, Lance M. Leslie, and Peter J. Lamb

Atlantic Ocean contributes the most to rainfall over western Sahel, whereas the Gulf of Guinea and the South Atlantic Ocean contribute the most over the central Sahel. Local evaporation is the second largest contributor to rainfall for both regions. Long et al. (2000) examine the large-scale forcing mechanisms in relation to initiation and maintenance of the Sahelian long-term drought. They analyzed rainfall, moisture flux, and vertical motion data and concluded that changes in the general circulation

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Zewdu T. Segele, Michael B. Richman, Lance M. Leslie, and Peter J. Lamb

, and national levels based on the climate system causation of Kiremt rainfall variability over Ethiopia. Time-scale analysis in Part I showed the contemporaneous linkages of Ethiopian rainfall variability with both atmospheric and sea surface temperature (SST) forcing during June–September (JJAS). The monsoon’s response to both slowly varying SST variability and higher-frequency regional atmospheric changes are found to be the primary climate system variability causation to assess Ethiopian

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Gang Zhang, Kerry H. Cook, and Edward K. Vizy

-permitting simulation. b. Diurnal cycle of rainfall in the simulation Figure 5 displays the percentage of daily rainfall distributed into 3-hourly intervals in the simulation for JJAS 2006. As in the observational analysis discussed in Part I , UTC is used as local time for this domain. Anomalously high afternoon rainfall near the eastern boundary (not shown) is neglected because it is spurious, being related to matching the model’s interior solution to the lateral boundary forcing. Over West Africa (west of 10°E

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