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David M. Lawrence, Keith W. Oleson, Mark G. Flanner, Christopher G. Fletcher, Peter J. Lawrence, Samuel Levis, Sean C. Swenson, and Gordon B. Bonan

are introduced in section 2 . In section 3 , we present an assessment of the surface climate simulation in CCSM4 with a focus on variables such as surface air temperature, precipitation, soil water storage, evapotranspiration, river discharge, and surface albedo as well as an assessment of the snow albedo feedback. In section 4 , we highlight results that emphasize several new earth system capabilities in CLM4. Specifically, we examine the urban heat island derived from the CLM4 urban canyon

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

those Southern Hemisphere rivers and enhancing rainfall over Northern Hemisphere river basins, such as the Orinoco, and over the northern tropical ocean. The northward migration of the ITCZ off the west coast of Africa contributes to the sea surface temperature (SST) increase in boreal spring by reducing wind speeds and suppressing evaporation. During this period, the westerly monsoon flow is expanded farther westward and moisture transport onto the continent is enhanced, increasing Sahel rainfall

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Christine A. Shields, David A. Bailey, Gokhan Danabasoglu, Markus Jochum, Jeffrey T. Kiehl, Samuel Levis, and Sungsu Park

(referred to as T31x3_1850_NOTMS in Fig. 3 ) shows roughly 10% larger magnitudes without it. Fig . 3. Zonal-mean zonal wind stress. LY represents an estimate based on the Large and Yeager (2009) dataset. b. Precipitation and river transport Annual-averaged precipitation rate across different model horizontal resolutions ( Fig. 4 ) is shown for the 1850 control runs. All three resolutions exhibit the signature double intertropical convergence zone also seen in CCSM3 ( Hack et al. 2006 ) and previous

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Susan C. Bates, Baylor Fox-Kemper, Steven R. Jayne, William G. Large, Samantha Stevenson, and Stephen G. Yeager

described in Large and Yeager (2009) . Most notably, the river runoff is now a 12-month climatology based on Dai et al. (2009) . The primary model solutions investigated are five ensemble members of the 20C fully coupled simulations of the CCSM4. They span the years 1850 through 2005 and include most of the CORE period (1948–2007). The simulations are forced with twentieth-century GHG emissions, prescribed aerosols, solar cycles, volcanic activity, and land use change ( Gent et al. 2011 ). Consistent

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Peter R. Gent, Gokhan Danabasoglu, Leo J. Donner, Marika M. Holland, Elizabeth C. Hunke, Steve R. Jayne, David M. Lawrence, Richard B. Neale, Philip J. Rasch, Mariana Vertenstein, Patrick H. Worley, Zong-Liang Yang, and Minghua Zhang

parameterizations. To improve the representation of permafrost, the thermal and hydrologic properties of organic soil are accounted for, and the ground column is extended to 50-m depth by adding five bedrock layers. The plant functional type distribution is as in Lawrence and Chase (2007) , except with a new cropping dataset. The river discharge has been separated into liquid and ice water streams. Heat from the ocean component is required to melt the ice and this has improved the global heat conservation of

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

compared to observations, to a CCSM3 20C ensemble mean, and to an ocean–sea ice hindcast experiment forced by observed winds. The ocean–sea ice hindcast simulation [Parallel Ocean Program–Coordinated Ocean-Ice Reference Experiments (“POP-CORE”)] was conducted using the CCSM4 ocean model POP (with a nominal 1° horizontal resolution) coupled to an active freely evolving dynamic–thermodynamic sea ice model [Los Alamos Sea Ice Model (CICE)]. Monthly climatological river runoff in the POP-CORE is based on

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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

variation is symmetric about the equator. The diurnal cycle of the daily, net shortwave heat flux depends on the solar zenith angle, which is determined from longitude, latitude, time of year, and the solar declination angle. As in CCSM3, a river transport model ( Oleson et al. 2010 ) routes runoff from the land surface to the ocean model via the flux coupler. These runoff fluxes are treated as surface freshwater fluxes, and they are distributed over coastal ocean points near the river mouths, with

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Kerry H. Cook, Gerald A. Meehl, and Julie M. Arblaster

from the ERA-Interim reanalysis. The Amazon basin precipitation maximum stretches across the continent from about 2°S and 70°W to the coast near 25°S and 45°W. The South Atlantic convergence zone (SACZ) extends diagonally off the continent over the South Atlantic Ocean, and there is a coastal maximum on the Atlantic coast near the mouth of the Amazon River. Note that the monsoon rainfall is clearly distinguished from the Atlantic marine ITCZ, which is located between the equator and 5°N. The strong

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Matthew C. Long, Keith Lindsay, Synte Peacock, J. Keith Moore, and Scott C. Doney

the observations reflect processes not in the models. For instance, large but localized negative biases in salinity-normalized DIC and alkalinity in the Atlantic and Indian Ocean basins reflect terrestrial carbon and weathering inputs from the Congo, Amazon, and Ganges/Brahmaputra Rivers that are not included in the model ( Fig. 1 ). b. Seasonality In the stratified subtropical ocean, seasonal variability in is predominantly related to changes in SST: summer warming increases , whereas winter

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David M. Lawrence, Andrew G. Slater, and Sean C. Swenson

) and methane ( Mastepanov et al. 2008 ) exchange, and the amplitude and timing of spring snowmelt river discharge peaks ( Rawlins et al. 2005 ; Kane et al. 2008 ). Frozen ground conditions are currently experiencing rapid change in response to late twentieth-century warming and associated climatic changes. Observed terrestrial Arctic changes (see Hinzman et al. 2005 for review) include warming and degrading of permafrost ( Romanovsky and Osterkamp 1997 ; Camill 2005 ; Åkerman and Johansson

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