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-dimensional linear remapping scheme ( Lipscomb 2001 ) transfers ice among ITD categories as needed because of thermodynamic, ridging, and advective ice thickness changes. In general, the physical parameterizations in the CCSM3 and CCSM4 ice components are quite similar. Major changes in the CCSM4 ice model include a new radiative transfer scheme, melt ponds and aerosols (all discussed below), a nonzero heat capacity snow cover, and an altered atmospheric boundary layer description that allows sensible heat
-dimensional linear remapping scheme ( Lipscomb 2001 ) transfers ice among ITD categories as needed because of thermodynamic, ridging, and advective ice thickness changes. In general, the physical parameterizations in the CCSM3 and CCSM4 ice components are quite similar. Major changes in the CCSM4 ice model include a new radiative transfer scheme, melt ponds and aerosols (all discussed below), a nonzero heat capacity snow cover, and an altered atmospheric boundary layer description that allows sensible heat
summed to obtain the total cloud fraction (see section 2c of the text). Within each panel, the clouds observed by MISR, ISSCP, and MODIS are divided into three column-integrated optical thickness ( τ ) categories: (left) all cloud, (middle) optically intermediate clouds (3.6 < τ < 23), and (right) optically thick clouds ( τ > 23). Differences in detected cloud amount for MODIS, ISCCP, and MISR are discussed in M10 and P12 (see also section 2d of the text). Values from this plot are
summed to obtain the total cloud fraction (see section 2c of the text). Within each panel, the clouds observed by MISR, ISSCP, and MODIS are divided into three column-integrated optical thickness ( τ ) categories: (left) all cloud, (middle) optically intermediate clouds (3.6 < τ < 23), and (right) optically thick clouds ( τ > 23). Differences in detected cloud amount for MODIS, ISCCP, and MISR are discussed in M10 and P12 (see also section 2d of the text). Values from this plot are
.9° × 2.5° horizontal resolution for 6 years for 2005 and 2100 conditions, with the last 5 years analyzed, to provide estimates of the aerosol forcings. Global aerosol forcings for direct and indirect effects differ strongly between 2006 and 2100 as RCPs project a “cleanup” of aerosol emissions to the atmosphere, and results are presented in Table 1 . Consistent with Lamarque et al. (2011) , the total aerosol optical depth (AOD) changes from ~0.12 in 2006 to ~0.10 in 2100, compared to a
.9° × 2.5° horizontal resolution for 6 years for 2005 and 2100 conditions, with the last 5 years analyzed, to provide estimates of the aerosol forcings. Global aerosol forcings for direct and indirect effects differ strongly between 2006 and 2100 as RCPs project a “cleanup” of aerosol emissions to the atmosphere, and results are presented in Table 1 . Consistent with Lamarque et al. (2011) , the total aerosol optical depth (AOD) changes from ~0.12 in 2006 to ~0.10 in 2100, compared to a
convective regions are introduced with new microphysics ( Fig. 10b ), particularly over land—not due to changes in cloud coverage (fraction), but due to a difference in how detrained condensate from convection is partitioned. In the subtropics (particularly the northern subtropics), the cloud microphysics change causes the largest increase in ACF ( Fig. 9c ). This does not show up as a cloud fraction change and is also due to how detrained condensate is treated (increased optical thickness owing to
convective regions are introduced with new microphysics ( Fig. 10b ), particularly over land—not due to changes in cloud coverage (fraction), but due to a difference in how detrained condensate from convection is partitioned. In the subtropics (particularly the northern subtropics), the cloud microphysics change causes the largest increase in ACF ( Fig. 9c ). This does not show up as a cloud fraction change and is also due to how detrained condensate is treated (increased optical thickness owing to
. They are forced by time series of solar output, greenhouse gases, several aerosols, and volcanic activity. The solar output anomaly time series is described in Lean et al. (2005) and is added to the 1360.9 W m −2 used in the 1850 control run. The CCSM4 volcanic activity is included by a time series of varying aerosol optical depths, exactly as in CCSM3 ( Ammann et al. 2003 ). The CO 2 and other greenhouse gases (methane and nitrous oxide) are specified as in the IPCC third assessment report
. They are forced by time series of solar output, greenhouse gases, several aerosols, and volcanic activity. The solar output anomaly time series is described in Lean et al. (2005) and is added to the 1360.9 W m −2 used in the 1850 control run. The CCSM4 volcanic activity is included by a time series of varying aerosol optical depths, exactly as in CCSM3 ( Ammann et al. 2003 ). The CO 2 and other greenhouse gases (methane and nitrous oxide) are specified as in the IPCC third assessment report
; Holland et al. 2012 ). Adjustments to ice albedos were required to simulate more reasonable ice extent and thickness values. Ice albedos designed for the x1 model are not appropriate for the low-resolution model and were decreased to compensate for excessive ice. In CCSM4, ice albedos are not adjusted directly but are computed using parameters representing optical properties of snow, bare sea ice, and melt ponds. These values are based on standard deviations from data obtained by the Surface Heat
; Holland et al. 2012 ). Adjustments to ice albedos were required to simulate more reasonable ice extent and thickness values. Ice albedos designed for the x1 model are not appropriate for the low-resolution model and were decreased to compensate for excessive ice. In CCSM4, ice albedos are not adjusted directly but are computed using parameters representing optical properties of snow, bare sea ice, and melt ponds. These values are based on standard deviations from data obtained by the Surface Heat
transfer across layers and also considers the radiative impact of aerosol deposition onto snow ( Flanner et al. 2007 ). Improvements to CLM that were included in CLM4 that were specifically aimed at improving the representation of permafrost in CCSM4 include an extension of the ground column to a depth of ~50 m by adding 5 bedrock layers below the original 10 soil layers ( Lawrence et al. 2008a ) and an explicit accounting of the thermal and hydrologic properties of organic soil ( Lawrence and Slater
transfer across layers and also considers the radiative impact of aerosol deposition onto snow ( Flanner et al. 2007 ). Improvements to CLM that were included in CLM4 that were specifically aimed at improving the representation of permafrost in CCSM4 include an extension of the ground column to a depth of ~50 m by adding 5 bedrock layers below the original 10 soil layers ( Lawrence et al. 2008a ) and an explicit accounting of the thermal and hydrologic properties of organic soil ( Lawrence and Slater
) reconstruction have significantly smaller aerosol optical depths in the Crowley et al. (2008) alternate reconstruction for PMIP3. Changes in total solar irradiance (TSI) are prescribed using the Vieira et al. (2011 ; hereafter VSK) reconstruction merged to Lean (2009) at 1834 to have a smooth transition to twentieth-century CCSM simulations. The VSK reconstruction is based on physical modeling of the solar surface magnetic flux and its relationship with the isotopes. An estimated 11-yr solar cycle
) reconstruction have significantly smaller aerosol optical depths in the Crowley et al. (2008) alternate reconstruction for PMIP3. Changes in total solar irradiance (TSI) are prescribed using the Vieira et al. (2011 ; hereafter VSK) reconstruction merged to Lean (2009) at 1834 to have a smooth transition to twentieth-century CCSM simulations. The VSK reconstruction is based on physical modeling of the solar surface magnetic flux and its relationship with the isotopes. An estimated 11-yr solar cycle
detailed in Park et al. (2012, unpublished manuscript). 3) Aerosol changes New consistent gridded emissions of reactive gases and aerosols for use in chemistry model simulations and needed by climate models for phase 5 of the Coupled Model Intercomparison Project (CMIP5) in support of the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5) are now available using the tropospheric MOZART (TROP-MOZART) framework in CAM ( Lamarque et al. 2010 ). These datasets are used to drive
detailed in Park et al. (2012, unpublished manuscript). 3) Aerosol changes New consistent gridded emissions of reactive gases and aerosols for use in chemistry model simulations and needed by climate models for phase 5 of the Coupled Model Intercomparison Project (CMIP5) in support of the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5) are now available using the tropospheric MOZART (TROP-MOZART) framework in CAM ( Lamarque et al. 2010 ). These datasets are used to drive
