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Alfredo Ruiz-Barradas and Sumant Nigam

case, model experiments suggest that the tropical component largely forces the central U.S. hydroclimate variability (e.g., Schubert et al. 2004 , 2009 ; Seager et al. 2005 ; Sutton and Hodson 2005 ); however, the nature of the tropical anomalies needs some clarification as they may be the result of extratropical activities. The influence of the oceans in generating precipitation variability in several models is obscured by their overactive local land surface–atmosphere interactions ( Ruiz

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Renu Joseph and Ning Zeng

hypothesis . Adv. Atmos. Sci. , 20 , 677 – 693 . Zeng , N. , and J. D. Neelin , 1999 : A land–atmosphere interaction theory for the tropical deforestation problem . J. Climate , 12 , 857 – 872 . Zeng , N. , J. D. Neelin , and C. Chou , 2000 : The first quasi-equilibrium tropical circulation model-implementation and simulation . J. Atmos. Sci. , 57 , 1767 – 1796 . Zeng , N. , H. Qian , E. Munoz , and R. Iacono , 2004 : How strong is carbon cycle-climate feedback under

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Rachel R. McCrary and David A. Randall

Pacific SSTs, 2) variations in tropical North Atlantic SSTs, and 3) land–atmosphere interactions that involve feedbacks between soil moisture and rainfall. Recently, modeling studies that use atmospheric global circulation models (AGCMs) forced with historic time series of global SSTs have implicated cool, La Niña–like conditions in the tropical Pacific as the primary cause of long-term Great Plains drought ( Schubert et al. 2004a , b ; Seager et al. 2005a , b , 2007 ; Cook et al. 2007 ; Seager et

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Siegfried Schubert, David Gutzler, Hailan Wang, Aiguo Dai, Tom Delworth, Clara Deser, Kirsten Findell, Rong Fu, Wayne Higgins, Martin Hoerling, Ben Kirtman, Randal Koster, Arun Kumar, David Legler, Dennis Lettenmaier, Bradfield Lyon, Victor Magana, Kingtse Mo, Sumant Nigam, Philip Pegion, Adam Phillips, Roger Pulwarty, David Rind, Alfredo Ruiz-Barradas, Jae Schemm, Richard Seager, Ronald Stewart, Max Suarez, Jozef Syktus, Mingfang Ting, Chunzai Wang, Scott Weaver, and Ning Zeng

al. 2004a , b ; Wang et al. 2008 , 2009 ) as well as numerous observationally based studies (e.g., Trenberth and Guillemot 1996 ; Mo et al. 1997 ; Ting and Wang 1997 ; Nigam et al. 1999 ; Koster et al. 2003 ; Ruiz-Barradas and Nigam 2004 ; McCabe et al. 2004 ; Wang et al. 2006 ) that have provided substantial insights into the nature of drought and the important role of both the oceans and land–atmosphere interactions. In particular, this work addresses the remaining uncertainties

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Alfredo Ruiz-Barradas and Sumant Nigam

, the models used, the SST forcing, and an overview of the results. The hierarchy of interactions that give rise to precipitation variability within a model, that is, local land surface–atmosphere versus remote SST–moisture fluxes, plays a crucial role in the simulation of regional summer hydroclimate variability. Regional hydroclimate over the central United States strongly depends on the moisture transport from the Gulf of Mexico via the Great Plains low-level jet, particularly in the summer

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Kirsten L. Findell and Thomas L. Delworth

Center for Ocean Land Atmosphere (COLA) and the University of Miami’s Rosenstiel School of Marine and Atmospheric Science for making the CCSM3.0 coupled model runs available. We would also like to thank Yana Malysheva for guaranteeing that the GFDL data were consistent with the CMOR protocol, and Paul Ginoux, Gabriel Vecchi, and four anonymous reviewers for their helpful comments on the manuscript. REFERENCES Alley , W. M. , 1984 : The Palmer Drought Severity Index: Limitations and assumptions

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Kingtse C. Mo, Jae-Kyung E. Schemm, and Soo-Hyun Yoo

–atmospheric interaction is not included. As demonstrated by Seager et al. (2000) , the SSTAs in the Atlantic can be influenced by the atmosphere. The tropical SSTAs over the North Atlantic are likely to be influenced by ENSO ( Mo and Hakkinen 2001 ; Saravanan and Chang 2000 , and many others). Therefore, both observations and experiments are utilized to study the influence of SSTAs on drought. Because drought implies persistent dryness, the 6-month SPI, SRI, and soil moisture anomalies are used to represent drought

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Philip J. Pegion and Arun Kumar

Ocean–Land–Atmosphere (COLA), and the University of Miami’s Rosenstiel School of Marine and Atmospheric Science for making the CCSM3.0 coupled model runs available. REFERENCES Alexander , M. A. , I. Bladé , M. Newman , J. R. Lanzante , N. C. Lau , and J. D. Scott , 2002 : The atmospheric bridge: The influence of ENSO teleconnections on air–sea interaction over the global oceans. J. Climate , 15 , 2205 – 2231 . Bacmeister , J. , P. J. Pegion , S. D. Schubert , and M. J

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Bradfield Lyon

net surface radiation, which serves as a control on surface evaporation and soil moisture is more closely tied to the evaporative fraction than to evaporation itself and this relationship is sensitive to the local soil moisture “regime” (e.g., Koster et al. 2009 ). Nonetheless, land surface–atmosphere interaction likely plays an important role in the joint occurrence of the two phenomena. In southern Africa this behavior is often seen, for example, during El Niño–Southern Oscillation (ENSO

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Randal D. Koster, Hailan Wang, Siegfried D. Schubert, Max J. Suarez, and Sarith Mahanama

-induced warming under global climate change ( Seneviratne et al. 2006 )]. In this sense, the results showcase the potentially complex interactions between ocean–land teleconnections and land-based hydroclimatic controls on evaporation. Acknowledgments This work was carried out as part of the U.S. CLIVAR Drought Working Group activity supported by NASA, NOAA, and NSF to coordinate and compare climate model simulations forced with a common set of idealized SST patterns. The authors thank NASA’s Global Modeling

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