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Anji Seth, Sara A. Rauscher, Michela Biasutti, Alessandra Giannini, Suzana J. Camargo, and Maisa Rojas

), related changes in the tropical tropospheric stability ( Chou et al. 2001 ; Neelin et al. 2003 ), and the regional effects of aerosols and black carbon ( Lau et al. 2006 ; Meehl et al. 2008 ). Despite the weakening of tropical circulations, the World Climate Research Programme (WCRP) phase 3 of the Coupled Model Intercomparison Project (CMIP3) multimodel climate projections suggested a tendency toward increased monsoon precipitation and increased low-level moisture convergence ( Christensen et al

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Hailong Liu, Chunzai Wang, Sang-Ki Lee, and David Enfield

1. Introduction The Atlantic warm pool (AWP), defined as the region with sea surface temperature (SST) above 28.5°C consisting of the Gulf of Mexico, the Caribbean Sea, and the western tropical North Atlantic, undergoes strong variations on seasonal to multidecadal time scales ( Wang and Enfield 2001 , 2003 ; Wang et al. 2008a , b ; Enfield and Cid-Serrano 2010 ). The AWP variability has been shown to play a role in the climate system by affecting precipitation patterns and tropical cyclone

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Gabriel A. Vecchi, Rym Msadek, Whit Anderson, You-Soon Chang, Thomas Delworth, Keith Dixon, Rich Gudgel, Anthony Rosati, Bill Stern, Gabriele Villarini, Andrew Wittenberg, Xiasong Yang, Fanrong Zeng, Rong Zhang, and Shaoqing Zhang

tropical cyclone climate? Geophys. Res. Lett. , 17 , 1917 – 1920 . Camargo , S. J. , A. G. Barnston , P. Klotzbach , and C. W. Landsea , 2007a : Seasonal tropical cyclone forecasts . WMO Bull. , 56 , 297 – 309 . Camargo , S. J. , K. A. Emanuel , and A. H. Sobel , 2007b : Use of a genesis potential index to diagnose ENSO effects on tropical cyclone genesis . J. Climate , 20 , 4819 – 4834 . Camargo , S. J. , M. Ting , and Y. Kushnir , 2013 : Influence of local and

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J. David Neelin, Baird Langenbrunner, Joyce E. Meyerson, Alex Hall, and Neil Berg

produce reductions in precipitation in the subtropics and precipitation increases at mid-to-high latitudes, and California is located in the region between these opposing tendencies ( Meehl et al. 2007 ). California's precipitation is also influenced by large-scale climate variability patterns such as El Niño–Southern Oscillation (ENSO) and the Pacific decadal oscillation. To address the effects of complex topography and other locally variable effects on precipitation, a common approach is to

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Paul A. Dirmeyer, Yan Jin, Bohar Singh, and Xiaoqin Yan

of the land surface onto the atmosphere during summer (e.g., Koster et al. 2004 ; Findell et al. 2011 ). Guo et al. (2011) showed that potential predictability from soil moisture is high over North America. North America also demonstrates the strongest improvement in prediction skill from the realistic initialization of the land surface for seasonal forecasts ( Koster et al. 2011 ). The location of maximum land–atmosphere coupling can vary in space ( Koster et al. 2011 ), and its strength can

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Justin Sheffield, Suzana J. Camargo, Rong Fu, Qi Hu, Xianan Jiang, Nathaniel Johnson, Kristopher B. Karnauskas, Seon Tae Kim, Jim Kinter, Sanjiv Kumar, Baird Langenbrunner, Eric Maloney, Annarita Mariotti, Joyce E. Meyerson, J. David Neelin, Sumant Nigam, Zaitao Pan, Alfredo Ruiz-Barradas, Richard Seager, Yolande L. Serra, De-Zheng Sun, Chunzai Wang, Shang-Ping Xie, Jin-Yi Yu, Tao Zhang, and Ming Zhao

indication of the dominant role of SST variability on TC–hurricane frequency variability. When assuming a persistence of SST anomalies, some of the models were also shown to exhibit significant skill in hurricane seasonal forecast (e.g., Zhao et al. 2010 ; Vecchi et al. 2011 ). Tropical storms and cyclones in this study are identified using the tracking method of Camargo and Zebiak (2002) , which uses low-level vorticity, surface winds, surface pressure, and atmospheric temperature and considers only

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Suzana J. Camargo

. Camargo , S. J. , K. A. Emanuel , and A. H. Sobel , 2007a : Use of a genesis potential index to diagnose ENSO effects on tropical cyclone genesis . J. Climate , 20 , 4819 – 4834 . Camargo , S. J. , H. Li , and L. Sun , 2007b : Feasibility study for downscaling seasonal tropical cyclone activity using the NCEP regional spectral model . Int. J. Climatol. , 27 , 311 – 325 . Camargo , S. J. , A. W. Robertson , S. J. Gaffney , P. Smyth , and M. Ghil , 2007c : Cluster

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Eric D. Maloney, Suzana J. Camargo, Edmund Chang, Brian Colle, Rong Fu, Kerrie L. Geil, Qi Hu, Xianan Jiang, Nathaniel Johnson, Kristopher B. Karnauskas, James Kinter, Benjamin Kirtman, Sanjiv Kumar, Baird Langenbrunner, Kelly Lombardo, Lindsey N. Long, Annarita Mariotti, Joyce E. Meyerson, Kingtse C. Mo, J. David Neelin, Zaitao Pan, Richard Seager, Yolande Serra, Anji Seth, Justin Sheffield, Julienne Stroeve, Jeanne Thibeault, Shang-Ping Xie, Chunzai Wang, Bruce Wyman, and Ming Zhao

effects occur because of greater snowfall and warming temperatures. The western United States is characterized by large intermodel variability in changes in the number of frost days, where MEM decreases in frost days (greater than 40 days) are also largest. Substantial intermodel spead exists for projections of how ENSO teleconnection changes will affect precipitation and temperature variability in western NA. Projected changes in seasonal mean Atlantic and east Pacific TC activity are inconsistent

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Zaitao Pan, Xiaodong Liu, Sanjiv Kumar, Zhiqiu Gao, and James Kinter

between the historical and historicalNat experiments. Figure 12 compares trends under different scenarios over different periods and seasons. The GHG forcing only has strong warming effects (0.12°–0.22°C decade −1 ) that may have partly compensated for cooling effects from the natural forcing in the all-forcing historical experiment. The historical experiment that incorporates both natural and anthropogenic forcing resulted in moderate warming as seen in the historical experiment. Fig . 12

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Leila M. V. Carvalho and Charles Jones

1. Introduction The presence of a monsoonal type of circulation involving intense convective activity and heavy precipitation is the dominant climatic feature in the tropical Americas during the respective summer seasons. The North American monsoon system (NAMS) and the South American monsoon system (SAMS) are often interpreted as the two extremes of the seasonal cycle of heat, moisture transport, and precipitation over the Americas ( Vera et al. 2006 ). The SAMS and NAMS seasonal cycles are

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