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Renu Joseph and Ning Zeng

changes as well as the changes in surface warming. Lambert and Allen (2009) analyze changes in precipitation for the whole globe, ocean, and land in several GCMs. They indicate precipitation changes over the oceans can be expressed as an energy balance between the direct and surface temperature–dependent effects of external climate forcings. However, precipitation over land is more complicated. Recent interest in the possible use of sulfate aerosols injected directly into the stratosphere to reduce

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Bradfield Lyon

upper and lower quartile values of the associated principal component (PC) time series were then used as thresholds to identify ENSO events, a definition used throughout this paper. An EOF analysis of the 3-month standardized precipitation index (SPI; McKee et al. 1993 ) was then performed based on model rainfall for all Southern Hemisphere land areas (10°N–55°S). The leading EOFs of both the SST and SPI fields related to ENSO had temporal correlations between the respective PC time series ranging

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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

experiments be performed that are designed to address some of the key issues outlined above using several different global climate models. A key objective was to be able to assess the model dependence of the results unambiguously. To accomplish that, it was proposed that each model be forced with the same set of idealized SST forcing anomalies. In addition, it was proposed that a control run be produced in which each model was forced with the same climatological SSTs. To allow an assessment of land

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M. Biasutti, A. H. Sobel, and Suzana J. Camargo

different answers ( Neelin et al. 2006 ; Christensen et al. 2007 ). The African monsoon is a case in point ( Cook 2008 ). The models of the third Coupled Model Intercomparison Project (CMIP3) used for the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC) disagree on the sign of future anomalies in the Sahel (see Fig. 1 and Biasutti and Giannini 2006 ; Cook and Vizy 2006 ; Lau et al. 2006 ). Although the median difference between the last 25 years of the twenty

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Kirsten L. Findell and Thomas L. Delworth

. , and Coauthors , 2008 : Use of FLUXNET in the Community Land Model development. J. Geophys. Res. , 113 , G01025 . doi:10.1029/2007JG000562 . Suppiah , R. , 2004 : Trends in the Southern Oscillation phenomenon and Australian rainfall and changes in their relationship. Int. J. Climatol. , 24 , 269 – 290 . Sutton , R. T. , and D. L. R. Hodson , 2005 : Atlantic Ocean forcing of North American and European summer climate. Science , 309 , 115 – 118 . Svoboda , M. , and

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

( Keyantash and Dracup 2002 ): Meteorological drought is related to P deficits, soil moisture deficits are used to identify agricultural drought, and hydrological drought is represented by a shortage of either streamflow or runoff. Many cooperative observation stations are available from 1900 to the present ( Wang et al. 2009 ), but long-term observational soil moisture and runoff are scarce. Therefore, soil moisture and runoff were obtained from the North American Land Data Assimilation System (NLDAS

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Caio A. S. Coelho and Lisa Goddard

, and the boreal summer [June–August (JJA)] season when El Niño events typically evolve. Because the seasonality often determines the relevance of El Niño impacts, particularly for precipitation, by examining only specific seasons some regional impacts might not be represented within this study. The analysis focuses on tropical land (30°N–30°S) and uses a simple meteorological interpretation of drought: below-normal precipitation based on a threshold of seasonally standardized precipitation. No

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

1. Introduction Anomalously dry periods are sometimes associated with anomalously warm periods, especially when considering summertime averages ( Namias 1960 ; Chang and Wallace 1987 ; Karl 1986 ; Huang et al. 1996 ; Durre et al. 2000 ; Shinoda and Yamaguchi 2003 ). The connection is through evaporation: drier soils can produce reduced evaporation and thus a reduced evaporative cooling of the land surface, which in turn leads to higher temperatures. The higher temperatures associated with

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