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Belen Rodríguez-Fonseca, Elsa Mohino, Carlos R. Mechoso, Cyril Caminade, Michela Biasutti, Marco Gaetani, J. Garcia-Serrano, Edward K. Vizy, Kerry Cook, Yongkang Xue, Irene Polo, Teresa Losada, Leonard Druyan, Bernard Fontaine, Juergen Bader, Francisco J. Doblas-Reyes, Lisa Goddard, Serge Janicot, Alberto Arribas, William Lau, Andrew Colman, M. Vellinga, David P. Rowell, Fred Kucharski, and Aurore Voldoire

, which probably remained from the strong 1982/83 El Niño event. Except for 1983, however, SST anomalies in the Indian Ocean at interannual time scales are generally weak in comparison to the other basins. Thus, the impact of Indian Ocean anomalies on Sahel rainfall could be masked by that of other basins. Palmer (1986) analyzed the AGCM response to SST anomalies in individual ocean basins that correspond to those in the SST pattern for the global tropics used in Folland et al. (1986) . The AGCM

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Bradfield Lyon

undertaken (e.g., Vizy and Cook 2003 ), the underlying physical mechanisms associated with regional and local rainfall and its variability have yet to be fully elucidated. Indeed, gaining a better physical understanding of what regulates the annual cycle of rainfall itself across the Greater Horn requires additional work. For example, why is the region semiarid despite its location in the deep tropics? Why do the long rains in MAM generate more rainfall (climatologically) than the “short rains” of OND

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Lixia Zhang and Tianjun Zhou

predictable than in the tropics because of the large contribution of internal atmospheric processes. Their work was based on the seasonal prediction experiment of the Climate and Ocean: Variability, Predictability and Change (CLIVAR) Seasonal Prediction Model Intercomparison Project II (SMIP II). High forecasting skill of surface temperature and precipitation is mostly seen in the tropics, while it is almost zero in East Asia, as derived from the Asia–Pacific Economic Cooperation (APEC) Climate Center

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Siegfried D. Schubert, Ronald E. Stewart, Hailan Wang, Mathew Barlow, Ernesto H. Berbery, Wenju Cai, Martin P. Hoerling, Krishna K. Kanikicharla, Randal D. Koster, Bradfield Lyon, Annarita Mariotti, Carlos R. Mechoso, Omar V. Müller, Belen Rodriguez-Fonseca, Richard Seager, Sonia I. Seneviratne, Lixia Zhang, and Tianjun Zhou

where SST anomalies are expected to influence annual mean precipitation and 2-m air temperature, based on the five atmospheric general circulation models (AGCMs: 12 ensemble members for each) forced with observed SST over the period 1979–2011. (See appendix A for descriptions of the models and their simulations.) The base maps show the fraction of the total interannual variance that is forced by SST. Focusing on precipitation ( Fig. 1 , top), we see that the ratios outside the tropics (poleward of

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Richard Seager and Martin Hoerling

as relatively low geopotential heights over the tropics. In the extratropics of the Northern Hemisphere there are wide areas of high pressure affecting North America in both cases—an expected response to cool tropical Pacific SST anomalies (e.g., Seager et al. 2003 ; Lu et al. 2008 ; L’Heureux and Thompson 2006 ). [The Southern Hemisphere height anomalies are probably dominated by trends caused, primarily, by ozone depletion ( Cai and Cowan 2007 ; Son et al. 2009 ; Polvani et al. 2011 ) and

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Mathew Barlow, Benjamin Zaitchik, Shlomit Paz, Emily Black, Jason Evans, and Andrew Hoell

Mediterranean Sea from 1902 to 2010, although the signal was somewhat mixed for the coastal Middle East. They then conducted a series of modeling runs that suggested that roughly half of the observed trend in that period was due to anthropogenic forcing and also that three aspects of SST forcing were important to the drying trend: uniform overall warming, warming of the tropics relative to the Northern Hemisphere extratropics, and warming of the tropical Indian Ocean relative to the tropical Pacific Ocean

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