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B. Samset, G. Myhre, AeroCom modellers (full list to be filled in)

Sensitivity of black carbon radiative forcing to vertical density profiles in AeroCom phase 2. Preliminary abstract:

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B. Samset, G. Myhre, AeroCom modellers (full list to be filled in)

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  1. Sensitivityofblackcarbon radiative forcing to verticaldensityprofiles in AeroComphase 2 Preliminary abstract: How much do differences in black carbon (BC) vertical density profiles contribute to the spread in modeled BC radiative forcing? We present a comparison of vertical direct shortwave forcing profiles based on output from X global aerosol models. The study is part of the AeroComphase 2 model intercomparison. Modeled 3D BC densities are converted to forcing fields by applying a common assumption about 3D forcing efficiency. This isolates variations due to vertical profiles from uncertainties due to clouds, water uptake and radiative transfer codes. We find that while there is a large spread in modeled vertical profiles, they contribute only XX% of the observed spread in globally averaged normalized BC forcings. While BC concentrations quickly decrease with altitude, BC forcing sensitivity increases due to the presence of water vapour, background aerosols and clouds. In consequence, models on average have 50% of their total BC forcing in levels above Xkm. B. Samset, G. Myhre, AeroCom modellers (full list to be filled in)

  2. Analysis outline • Take as input the 3D concentrations (mmrfields + 3D level info) ofanthropogenicBC and/or BCFF from themodelsubmissions • Use 3D profilesofnormalized BC forcing from a single model (OsloCTM2, seeSamset and Myhre, GRL, 2011) • Calculate 3D BC forcingfields from themodelconcentrations and 3D NDRF profiles • Divide zonalmean BC forcing by burden to getnewnormalizedforcingdistributions • The spread in thesedistributionsindicatestheimportanceoftheverticalprofile.Other info such as themodeled BC sensitivity, clouds etc. arecontained in theexternal NDRF profile. • The presentation shows: • 3-9: The concentration and BC(FF) forcing 2D fields from eachmodel • 10-12:The concentrationprofilesand RF verticalprofiles, for global mean and twoillustrative regions (Europe and the Arctic) • 13: Normalizedforcingzonalmean, extracted from dividingtheforcing and burdenzonalmeansshown in the 2D fields (green lines) • 14: A tablewiththe global meananthropogenic BC(FF) burdens, RFs and NRFs

  3. Concentration and BC(FF) fields:INCA BC and BCFF 2D: RF per height (colormap)Line: RF zonalmean (right axis) 2D: Concentration (colormap)Line: Burdenzonalmean (right axis)

  4. Concentration and BC(FF) fields:OsloCTM2 BC and BCFF 2D: RF per height (colormap)Line: RF zonalmean (right axis) 2D: Concentration (colormap)Line: Burdenzonalmean (right axis)

  5. Concentration and BC(FF) fields:CAM4-Oslo BC and BCFF 2D: RF per height (colormap)Line: RF zonalmean (right axis) 2D: Concentration (colormap)Line: Burdenzonalmean (right axis)

  6. Concentration and BC(FF) fields:SPRINTARS BC and BCFF 2D: RF per height (colormap)Line: RF zonalmean (right axis) 2D: Concentration (colormap)Line: Burdenzonalmean (right axis)

  7. Concentration and BC(FF) fields:MPIHAM_V2 BC and BCFF 2D: RF per height (colormap)Line: RF zonalmean (right axis) 2D: Concentration (colormap)Line: Burdenzonalmean (right axis)

  8. Concentration and BC(FF) fields:HadGEM2-ES BC and BCFF 2D: RF per height (colormap)Line: RF zonalmean (right axis) 2D: Concentration (colormap)Line: Burdenzonalmean (right axis)

  9. Concentration and BC(FF) fields:GISS-modelE BC and BCFF 2D: RF per height (colormap)Line: RF zonalmean (right axis) 2D: Concentration (colormap)Line: Burdenzonalmean (right axis)

  10. RF verticalprofiles: Global b) c) d) Concentrationprofile RF per height, divided by theglobal meanburden Integrated forcingfraction Forcingfraction infourheightlayers I = INCA O = OsloCTM2 C = CAM4-Oslo S = SPRINTARS M = MPIHAM H = HadGEM2-ES G = GISS-modelE

  11. RF verticalprofiles: Europe b) c) d) Concentrationprofile RF per height, divided by theglobal meanburden Integrated forcingfraction Forcingfraction infourheightlayers I = INCA O = OsloCTM2 C = CAM4-Oslo S = SPRINTARS M = MPIHAM H = HadGEM2-ES G = GISS-modelE

  12. RF verticalprofiles: Arctic b) c) d) Concentrationprofile RF per height, divided by theglobal meanburden Integrated forcingfraction Forcingfraction infourheightlayers I = INCA O = OsloCTM2 C = CAM4-Oslo S = SPRINTARS M = MPIHAM H = HadGEM2-ES G = GISS-modelE

  13. Normalizedforcingzonalmean • Model BC concentrationwascombinedwithexternalnormalizedforcingprofile • Forcingzonalmeanwascalculated • NRF zonalmean is forcingzonalmeandivided by modeledburdenzonalmean(bothcurvescan be seen in theconcentration and RF 2D plots) • The spreadhere shows theeffectofdifference in verticalprofileonly

  14. Burdens, RFs, NRFs BC BCFF • Burdens, hereextracted from themmrfields, areidentical to the 2D burdenfields used in themainAeroComdirectRF intercomparison • RF is generallystrongerthan in theAeroComintercomparison, due to theOsloCTM2 NRF profilebeingquitestrong

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