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Samantha Stevenson, Baylor Fox-Kemper, Markus Jochum, Richard Neale, Clara Deser, and Gerald Meehl

members of an ensemble to be considered simultaneously, so that the effects of intrinsic multidecadal ENSO variations can be averaged out as they would be in a longer simulation. However, all of the ensemble members experience the same rapid radiative forcing changes, which are followed by a delay in adjustment of the tropical thermocline. The time scale of these tropical thermocline changes cannot be shortened by increasing the ensemble size. In state-of-the-art general circulation models (GCMs), the

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Clara Deser, Adam S. Phillips, Robert A. Tomas, Yuko M. Okumura, Michael A. Alexander, Antonietta Capotondi, James D. Scott, Young-Oh Kwon, and Masamichi Ohba

the tropical Pacific to the extratropics, variability originating in the North Pacific may also influence the tropical Pacific via the atmosphere (e.g., Pierce et al. 2000 ) and the ocean (e.g., Kleeman et al. 1999 ). Based on analyses of an extended coupled model simulation, Vimont et al. (2001 , 2003a) proposed an extratropical-to-tropical connection termed the “seasonal footprinting mechanism” (SFM), where internal fluctuations in the atmospheric circulation over the North Pacific during

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Gokhan Danabasoglu, Susan C. Bates, Bruce P. Briegleb, Steven R. Jayne, Markus Jochum, William G. Large, Synte Peacock, and Steve G. Yeager

. This is because these order 150-yr experiments are too short to produce any significant departures at depth from their initial conditions. In this work, we present mostly time-mean results. Other aspects of the ocean model solutions from CCSM4 simulations are discussed in several Journal of Climate CCSM4 Special Issue papers. These include papers on multidecadal variability in the North Atlantic with a focus on the Atlantic meridional overturning circulation (AMOC) (Danabasoglu et al. 2011

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Alicia R. Karspeck, Steve Yeager, Gokhan Danabasoglu, Tim Hoar, Nancy Collins, Kevin Raeder, Jeffrey Anderson, and Joseph Tribbia

development is part of a broader initiative at the National Center for Atmospheric Research (NCAR) to build assimilation capabilities for the atmosphere, land, sea ice, and ocean components of the community model. There is currently an array of global ocean assimilation products available to the climate-science community that employ various ocean general circulation models and assimilation algorithms. The assimilation methods used to construct these products are all least squares methods that attempt to

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Wilbert Weijer, Bernadette M. Sloyan, Mathew E. Maltrud, Nicole Jeffery, Matthew W. Hecht, Corinne A. Hartin, Erik van Sebille, Ilana Wainer, and Laura Landrum

the thermocline and are important components of the upper-ocean nutrient cycle, impacting the efficiency of the global marine ecosystem ( Sloyan and Rintoul 2001a ; Sarmiento et al. 2004 ). The Southern Ocean plays an important role as a conduit for the interbasin exchange of water masses and properties ( Rintoul et al. 2001 ; Meredith et al. 2011 ). Most of this exchange is accomplished by the ACC, which is the strongest ocean current in the global ocean. Because of the lack of a closed

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Semyon A. Grodsky, James A. Carton, Sumant Nigam, and Yuko M. Okumura

defines the boundary between the southeasterly and northeasterly trade wind systems. As the ITCZ shifts northward in northern summer from its annual mean latitude a few degrees north of the equator, the zonal winds along the equator intensify, increasing the zonal tilt of the oceanic thermocline and bringing cool water into the mixed layer of the eastern equatorial ocean (e.g., Xie and Carton 2004 ). This northward shift reduces rainfall into the Amazon and Congo basins, reducing the discharge of

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Gerald A. Meehl, Julie M. Arblaster, Julie M. Caron, H. Annamalai, Markus Jochum, Arindam Chakraborty, and Raghu Murtugudde

1. Introduction Monsoons are central to the seasonal development of tropical rainfall maxima that encompass local, regional, and large-scale atmospheric and ocean circulation patterns. Their year to year variability, and connections between the monsoon regimes themselves as well as to extratropical weather and climate, make monsoon simulations an important part of any climate model. This is the first of a series of two papers that document monsoon regimes and associated processes for the

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Ernesto Muñoz, Wilbert Weijer, Semyon A. Grodsky, Susan C. Bates, and Ilana Wainer

–sea–land dynamics ( Schouten et al. 2005 ). For example, when the precipitation is greatest over the equatorial Amazon in boreal spring, the equatorial easterlies are weak and Atlantic SSTs are quasi-uniform in the near-equatorial belt. As the seasons progress, the ITCZ shifts northward and stronger southeasterly winds amplify the eastward tilt of the thermocline, leading (through upwelling and Kelvin waves) to a colder eastern equatorial Atlantic in late spring and early summer. Farther north in the Caribbean

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Esther C. Brady, Bette L. Otto-Bliesner, Jennifer E. Kay, and Nan Rosenbloom

overturning circulation in CCSM4 . J. Climate , 25 , 5153 – 5172 . Deser , C. , and Coauthors , 2012 : ENSO and Pacific decadal variability in Community Climate System Model version 4 . J. Climate , 25 , 2622 – 2651 . de Vernal , A. , and C. Hillaire-Marcel , 2000 : Sea-ice cover, sea-surface salinity and halo-/thermocline structure of the northwest North Atlantic: Modern versus full glacial conditions . Quat. Sci. Rev. , 19 , 65 – 85 . Edwards , T. L. , M. Crucifix , and S. P

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Shih-Yu Wang, Michelle L'Heureux, and Jin-Ho Yoon

) and off-equatorial Rossby waves could subsequently impact tropical low-level winds and the equatorial thermocline, initiating the onset of ENSO. In addition, Anderson (2004) and Anderson and Maloney (2006) show that wind stress anomalies induced by the NPO may also have a concurrent influence on subsurface temperatures and heat content across the central and eastern tropical Pacific, which can persist and subsequently influence the overlying SSTAs throughout the following year. The occurrence

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