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Omar V. Müller, Ernesto Hugo Berbery, Domingo Alcaraz-Segura, and Michael B. Ek

convective schemes, the decision to activate or not activate deep convection in BMJ is not based entirely upon cloud layer moisture. The reference profiles for the BMJ scheme are calculated by lifting parcels from the boundary layer, so their time dependence responds directly to the land surface forcing and the time dependent response of the mixed layer. For these reasons, alterations to conditions within the planetary boundary layer have an effect on the simulations (K. Betts and Z. Janjić 2013

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Richard Seager and Martin Hoerling

/SOURCES/.LDEO/.ClimateGroup/.PROJECTS/ .) In addition, to focus on variations, especially of soil moisture, in the post-1979 period we use two global atmospheric models with SST, sea ice, and external radiative forcing specified as monthly time-evolving boundary conditions from January 1979 to December 2012. One model used is the NCAR Community Atmosphere Model version 4 (CAM4) global climate model ( Gent et al. 2011 ), with the simulations performed at a 1° resolution and 26 atmospheric levels, and for which a 20-member ensemble is

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Siegfried D. Schubert, Hailan Wang, Randal D. Koster, Max J. Suarez, and Pavel Ya. Groisman

slowly varying ocean boundary conditions contributed substantially to the magnitude of the event. They also stated that “severe drought occurred with the Russian heat wave, making it likely that land surface feedbacks amplified this heat wave’s intensity.” Trenberth and Fasullo (2012) , in contrast, linked the unusual anticyclone to the development of a large-scale Rossby wave train—suggesting that the wave train was forced by anomalous convection in the tropical Atlantic and northern Indian Oceans

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

to occur in marginal lands of southwest Asia—primarily in the southern Arabian Peninsula and in the Fertile Crescent and Anatolia regions of Turkey, Syria, and Iraq. In a regional modeling study of drought, Zaitchik et al. (2007) found that under drought conditions vegetation dieback in the semiarid zone of Syria and Iraq leads to an increase in albedo, a reduction in sensible heat flux, and a tendency toward lower surface temperatures, a shallower planetary boundary layer, and reduced cloud

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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

X. Chen , 2013 : The 2012 north China floods: Explaining an extreme rainfall event in the context of a long-term drying tendency . Bull. Amer. Meteor. Soc. , 94 ( 9 ), S49 – S51 , doi: 10.1175/BAMS-D-13-00085.1 . Zwiers , F. W. , X. L. Wang , and J. Sheng , 2000 : Effects of specifying bottom boundary conditions in an ensemble of atmospheric GCM simulations . J. Geophys. Res. , 105 , 7295 – 7315 , doi: 10.1029/1999JD901050 . 1 The GDIS was developed as one of the key

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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

variability at decadal time scales. Using observed SSTs as boundary conditions, most AGCMs are able to reproduce the twentieth-century drying trend in West Africa and the Sahel drought of the 1970–80s and subsequent rainfall recovery ( Rowell 1996 ; Giannini et al. 2003 ; Bader and Latif 2003 ; Lu and Delworth 2005 ; Haarsma et al. 2005 ; Hoerling et al. 2006 , 2010 ; Lu 2009 ; Tippett 2006 ; Tippett and Giannini 2006 ; Caminade and Terray 2010 ; Mohino et al. 2011a ; see also Fig. 8 ). The

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Bradfield Lyon

their boundary conditions. A more general and fundamental question is how tropical Pacific SSTs will be affected by climate change. The La Niña–like pattern of tropical Pacific SSTs associated with recent decadal variability is similar to longer-term trends in SSTs. Several studies report a strengthening of the Walker circulation over the Pacific ( Chen et al. 2002 ; Compo and Sardeshmukh 2010 ; Solomon and Newman 2012 ; L’Heureux et al. 2013 ), not a weakening. Whether these trends continue or

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Lixia Zhang and Tianjun Zhou

1970s, aridity over north China has increased substantially, and the extreme drought frequency is increasing in the central part of northern China, northeast China, and the eastern part of northwest (NW) China ( Ma and Fu 2006 ). Because of the increasing drought, the grassland area of Jilin Province (41°–46°N, 122°–131°E) is decreasing at a rate of 2.8% per year, the semiarid boundary of northern China has shifted southeastward during the last 50 years (1950–98), and the discharge of the Yellow

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