Sensitivity of black carbon radiative
forcing to vertical density profiles in
AeroCom phase 2
B. Samset, G. Myhre, AeroCom modellers
(full list to be filled in)
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
AeroCom phase 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.
Analysis outline
• Take as input the 3D concentrations (mmr fields + 3D level info) of anthropogenic
BC and/or BCFF from the model submissions
• Use 3D profiles of normalized BC forcing from a single model (OsloCTM2, see
Samset and Myhre, GRL, 2011)
• Calculate 3D BC forcing fields from the model concentrations and 3D NDRF profiles
• Divide zonal mean BC forcing by burden to get new normalized forcing distributions
• The spread in these distributions indicates the importance of the vertical profile.
Other info such as the modeled BC sensitivity, clouds etc. are contained in the
external NDRF profile.
• The presentation shows:
• 3-9: The concentration and BC(FF) forcing 2D fields from each model
• 10-12:The concentration profiles and RF vertical profiles, for global mean and two
illustrative regions (Europe and the Arctic)
• 13: Normalized forcing zonal mean, extracted from dividing the forcing and
burden zonal means shown in the 2D fields (green lines)
• 14: A table with the global mean anthropogenic BC(FF) burdens, RFs and NRFs
Concentration and BC(FF) fields:
INCA BC and BCFF
2D: Concentration (color map)
Line: Burden zonal mean (right axis)
2D: RF per height (color map)
Line: RF zonal mean (right axis)
Concentration and BC(FF) fields:
OsloCTM2 BC and BCFF
2D: Concentration (color map)
Line: Burden zonal mean (right axis)
2D: RF per height (color map)
Line: RF zonal mean (right axis)
Concentration and BC(FF) fields:
CAM4-Oslo BC and BCFF
2D: Concentration (color map)
Line: Burden zonal mean (right axis)
2D: RF per height (color map)
Line: RF zonal mean (right axis)
Concentration and BC(FF) fields:
SPRINTARS BC and BCFF
2D: Concentration (color map)
Line: Burden zonal mean (right axis)
2D: RF per height (color map)
Line: RF zonal mean (right axis)
Concentration and BC(FF) fields:
MPIHAM_V2 BC and BCFF
2D: Concentration (color map)
Line: Burden zonal mean (right axis)
2D: RF per height (color map)
Line: RF zonal mean (right axis)
Concentration and BC(FF) fields:
HadGEM2-ES BC and BCFF
2D: Concentration (color map)
Line: Burden zonal mean (right axis)
2D: RF per height (color map)
Line: RF zonal mean (right axis)
Concentration and BC(FF) fields:
GISS-modelE BC and BCFF
2D: Concentration (color map)
Line: Burden zonal mean (right axis)
2D: RF per height (color map)
Line: RF zonal mean (right axis)
RF vertical profiles: Global
a)
b)
c)
d)
(a) Concentration
profile
(b) RF per height,
divided by the
global mean
burden
(c) Integrated forcing
fraction
(d) Forcing fraction in
four height layers
I = INCA
O = OsloCTM2
C = CAM4-Oslo
S = SPRINTARS
M = MPIHAM
H = HadGEM2-ES
G = GISS-modelE
RF vertical profiles: Europe
a)
b)
c)
d)
(a) Concentration
profile
(b) RF per height,
divided by the
global mean
burden
(c) Integrated forcing
fraction
(d) Forcing fraction in
four height layers
I = INCA
O = OsloCTM2
C = CAM4-Oslo
S = SPRINTARS
M = MPIHAM
H = HadGEM2-ES
G = GISS-modelE
RF vertical profiles: Arctic
a)
b)
c)
d)
(a) Concentration
profile
(b) RF per height,
divided by the
global mean
burden
(c) Integrated forcing
fraction
(d) Forcing fraction in
four height layers
I = INCA
O = OsloCTM2
C = CAM4-Oslo
S = SPRINTARS
M = MPIHAM
H = HadGEM2-ES
G = GISS-modelE
Normalized forcing zonal mean
• Model BC concentration was
combined with external normalized
forcing profile
• Forcing zonal mean was calculated
• NRF zonal mean is forcing zonal
mean divided by modeled burden
zonal mean
(both curves can be seen in the
concentration and RF 2D plots)
• The spread here shows the effect
of difference in vertical profile only
Burdens, RFs, NRFs
BC
Model
INCA
OsloCTM2
CAM4-Oslo
SPRINTARS
MPIHAM
HadGEM
GISS-modelE
BCFF
Burden RF
NRF
0.226 0.414 1830
0.198 0.398 2000
0.351
0.85 2420
0.291 0.536 1840
0.176 0.263 1490
0.37 0.809 2190
0.212 0.403 1910
Model
INCA
OsloCTM2
CAM4-Oslo
Burden RF
NRF
0.154 0.283 1830
0.167 0.337 2020
0.213 0.513 2410
• Burdens, here extracted from the mmr
fields, are identical to the 2D burden
fields used in the main AeroCom direct
RF intercomparison
• RF is generally stronger than in the
AeroCom intercomparison, due to the
OsloCTM2 NRF profile being quite
strong