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J. Paul Spence, Michael Eby, and Andrew J. Weaver

important oceanic processes are not adequately represented at coarse (>1°) resolution. For example, the widths of boundary currents are overestimated, while their speeds are underestimated, and the influence of mesoscale eddies are fairly crudely parameterized. The Intergovernmental Panel on Climate Change (IPCC) Third Assessment Report (TAR) warned that model results reliant on meridional heat transports with >1° resolution ocean components should be treated cautiously ( McAvaney et al. 2001 ). The

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Michael S. Pritchard, Andrew B. G. Bush, and Shawn J. Marshall

. The large-scale dynamics of the ice sheet are strongly controlled by climatological boundary conditions imposed at the ice sheet surface. Owing to the seasonality of ablation and accumulation, this forcing is conventionally imposed through a set of monthly mean temperature and precipitation fields representing a climatological annual cycle. These are horizontally downscaled from the coarse atmospheric model grid to the higher-resolution ice sheet model grid using 2D cubic spline interpolation. The

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Guido Vettoretti, Marc d’Orgeville, William R. Peltier, and Marek Stastna

possible mechanisms that may contribute to the behavior of this mode of variability under changing boundary conditions (e.g., Timmermann et al. 2007 ). If fidelity in modeling the variability of ENSO in response to changes of the AMOC can be established for past events, we may then have increased confidence in the projected impact upon this crucial phenomenon in global warming calculations. Examining ENSO from the perspective of coupled climate model predictions under past, present, and future climate

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Garry K. C. Clarke, Andrew B. G. Bush, and John W. M. Bush

1/3 , where R H = S / P is the hydraulic radius of the channel. The discharge is simply Q = υS and, at steady state, is constant at Q 0 along the entire length of the channel if inflow from tributary channels is negligible. To characterize the hydraulic roughness of the channel, we take n = 0.03 m −1/3 s, a representative value for rivers. For the upstream ( s = 0) boundary conditions we take S (0, t ) = S 0 and υ (0, t ) = Q 0 / S 0 , where Q 0 is the paleohydraulic

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Alex S. Gardner, Martin J. Sharp, Roy M. Koerner, Claude Labine, Sarah Boon, Shawn J. Marshall, David O. Burgess, and David Lewis

performed either by running a regional climate model (forced at its boundaries with coarse-resolution climate model output or data from climate reanalysis) at the desired resolution or by computing near-surface temperatures from climate model fields using a digital elevation model of the glacier surface and an assumed temperature lapse rate. “Lapse rate” is defined as “the decrease of an atmospheric variable with height, the variable being temperature, unless otherwise specified” ( Glickman 2000 ), and

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Shawn J. Marshall and Martin J. Sharp

periods during the melt season. This keeps the surface temperature near 0°C and it dampens near-surface temperature variability, relative to the diurnal and synoptic weather-induced variability that characterizes near-surface boundary layer temperatures over subzero snow and ice surfaces. This summer reduction in monthly and daily temperature variability means that annual average values of σ m and σ d are not representative of melt-season conditions. The lower values observed in summer months are

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Marc d’Orgeville and W. Richard Peltier

. doi:10.1126/science.1109496 . Timmermann , A. , M. Latif , R. Voss , and A. Grötzner , 1998 : Northern Hemispheric interdecadal variability: A coupled air–sea mode. J. Climate , 11 , 1906 – 1931 . Trenberth , K. E. , and D. J. Shea , 2006 : Atlantic hurricanes and natural variability in 2005. Geophys. Res. Lett. , 33 , L12704 . doi:10.1029/2006GL026894 . Weaver , A. E. , and E. S. Sarachik , 1991 : The role of mixed boundary conditions in numerical models of the

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Stephen D. Griffiths and W. Richard Peltier

; Griffiths and Peltier 2008 ; Arbic et al. 2008 ). Such changes can impact the climate system in a variety of ways. Globally, of interest is the history of tidal dissipation, which is mainly associated with energy loss to a turbulent bottom boundary layer in shallow seas ( Taylor 1920 ) and conversion to internal tides in the deep ocean (e.g., Garrett and Kunze 2007 ). Tidal dissipation implies a slowing of the earth’s rotation rate and a corresponding recession of the moon, variations in which can be

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Marc d’Orgeville and W. Richard Peltier

( Boccaletti et al. 2005 ). Although the understanding of tropical–extratropical teleconnections on decadal time scales is of primary importance in the study of the decadal modulation of the El Niño–Southern Oscillation phenomenon, these teleconnections do not seem to constitute sufficient conditions for the existence of the PDO. Indeed, AOGCM simulations deliver a reasonable depiction of the PDO, even in the absence of any strong connection to the tropical Pacific (i.e., Alexander et al. 2006 ; Latif

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Garry K. C. Clarke, Etienne Berthier, Christian G. Schoof, and Alexander H. Jarosch

flux can be calculated and the balance flux can be inverted to ice thickness using Glen’s flow law ( Huss et al. 2008 ). A shortcoming of the volume–area scaling approach is that it yields no useful information about subglacial topography—a necessary boundary condition for glacier dynamics models. In contrast, the physics-based methods allow ice thickness to be estimated but are subject to error if their underlying assumptions are not fulfilled. This motivates our interest in a fresh approach to

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