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Gerhard Krinner, Bérangère Guicherd, Katia Ox, Christophe Genthon, and Olivier Magand

the atmospheric model remains global, although it is focused on the region of interest. The required boundary conditions that differ between the present and future model runs are then essentially the atmospheric composition (in particular greenhouse gas concentrations) and sea surface conditions (SSC), that is, sea surface temperature (SST) and sea ice concentration (SIC). There are two basic methods of prescribing present and future sea surface conditions. The first method consists in using

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Oliver Timm and Axel Timmermann

insight into the climate response to different forcing can be gained from time-slice experiments using constant boundary conditions ( Kutzbach and Otto-Bliesner 1982 ; Broccoli and Manabe 1987 ; Kutzbach and Liu 1997 ; Joussaume et al. 1999 ; Pinot et al. 1999 ; Hostetler and Mix 1999 ; Shin et al. 2003 ; Kim et al. 2003 ; Timmermann et al. 2004 ; Peltier and Solheim 2004 ; Renssen et al. 2004 ; Otto-Bliesner et al. 2006 ), the nonequilibrated (transient) climate trajectories are difficult

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Yongkang Xue, Ratko Vasic, Zavisa Janjic, Fedor Mesinger, and Kenneth E. Mitchell

surface boundary conditions from specification or prediction by a coupled ocean and/or land surface model, as well as by lateral boundary conditions (LBCs) from a GCM or reanalysis at regular temporal intervals. In this paper, we will refer to this lateral nesting approach as the dynamic downscaling method (DDM). There are a number of issues concerning the use of the DDM ( Laprise et al. 2000 ; Denis et al. 2002 ). The most important issue is whether, and if so under what conditions, the DDM is

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A. Timmermann, S. J. Lorenz, S-I. An, A. Clement, and S-P. Xie

Pacific. Our focus is on the relevant mechanisms rather than on the detailed past climate trajectory. Hence, the results should not be directly compared to paleo-proxy records for ENSO. Further studies have to be conducted in the future to take into account the role of other time-varying boundary conditions ( Timm and Timmermann 2007 ). The paper is organized as follows. In section 2 the CGCM is described. Section 3 presents the basic mechanism of orbitally driven ENSO variance changes. In

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Ruth Cerezo-Mota, Myles Allen, and Richard Jones

situation. However, owing to the lack of observations it is very difficult to determine the fidelity of such models or that of the boundary conditions from general circulation models (GCMs) used to drive the regional models. The Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC) recognized that current GCMs have systematic biases, especially in the simulation of regional features in areas with complex terrain such as the NAM region ( Cavazos and Marengo 2009

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A. Colin de Verdière, M. Ben Jelloul, and F. Sévellec

-flop oscillations found by Welander with external parameters (such as the values of the variables in the reservoirs of Welander’s model) kept to a minimum. The simplest addition that comes to mind was to add two deep boxes to the Stommel model. Such a 2 × 2 model shows the collapse phase of the THC when the salinity forcing is strong enough but remains in that collapsed “haline mode” under constant boundary conditions. Whatever the initial and forcing conditions, no oscillatory states were ever found. The

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Vasubandhu Misra

that complex topography and coastline features have a strong impact on the reproducibility of small-scale climate features that a RCM can resolve. But, with the growing use of RCMs it is also becoming apparent that the RCM integrations are limited by the errors in forcing from the lateral boundary conditions (LBCs; Risbey and Stone 1996 ; Noguer et al. 1998 ; Christensen et al. 1998 ; Menendez et al. 2001 ; Misra et al. 2003 ). Furthermore, Christensen et al. (1998) indicate that the

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Matthew Collins and Myles R. Allen

ocean state that is crucial in the first-kind predictability of climate since this provides the possible “memory” of the system (although other factors such as variations in land cover may be important). Predictability of the second kind focuses on the boundary value problem: how predictable changes in the boundary conditions that affect climate can provide predictive power. A common class of second-kind predictability studies use atmosphere models with prescribed sea surface temperatures (SSTs) in

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Wanli Wu, Amanda H. Lynch, and Aaron Rivers

interface plays a fundamental role in most mesoscale circulations. The global analysis and global model output themselves contain biases. Interpolations are usually required to preprocess the global data onto regional model grids. The resulting inaccuracies pass through the mesh interface and have the potential to penetrate into the interior of the regional model domain. The accuracy of regional model simulations is then limited by the accuracy of the initial and lateral boundary conditions obtained

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Martin Hoerling, James Hurrell, Arun Kumar, Laurent Terray, Jon Eischeid, Philip Pegion, Tao Zhang, Xiaowei Quan, and TaiYi Xu

aforementioned studies in that we estimate the statistics of decadal North American climate that are consistent with various plausible scenarios of boundary conditions, whereas most other studies to date have followed an ensemble of integrations from a specific, observed initial state. Our forecast is thus constrained solely by the signal associated with the expected change in boundary conditions related to future anthropogenic greenhouse gas (GHG) forcing. A probabilistic decadal prediction is generated

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