Aerosol Indirect Effects in CAM and MIRAGE
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Transcript of Aerosol Indirect Effects in CAM and MIRAGE
Aerosol Indirect Effects in CAM and MIRAGE
Steve Ghan
Pacific Northwest National Laboratory
Jean-Francois Lamarque, Peter Hess, and Francis Vitt, NCAR
Indirect Effects Physics
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∂Nk
∂t= −(V • ∇N )k −
∂ρ ′ w ′ N
ρ∂z
⎛
⎝ ⎜
⎞
⎠ ⎟k
+ Sk − Ak −Ck − Ek
Nk = droplet number mixing ratio in layer k
Ak = droplet loss by autoconversion of droplets
Ck = droplet loss by collection by precipitation
Ek = droplet loss by evaporation
Sk = droplet nucleation source in layer k
Indirect Effects Physics
€
∂Nk
∂t= −(V • ∇N )k −
∂ρ ′ w ′ N
ρ∂z
⎛
⎝ ⎜
⎞
⎠ ⎟k
+ Sk − Ak −Ck − Ek
Nk = droplet number mixing ratio in layer k
Ak = droplet loss by autoconversion of droplets
Ck = droplet loss by collection by precipitation
Ek = droplet loss by evaporation
Sk = droplet nucleation source in layer k
f = cloud fraction
w = updraft velocity
Nn = number nucleated (parameterized in terms of w and aerosol)
p(w) = probability density function of w
w* = σw= characteristic updraft velocity in growing part of cloud
€
=max( fk − fk−1,0)
zk+ 1
2− z
k−12
wNnwmin
∞
∫ (w)p(w)dw +∂fk
∂tNn(w*)
Indirect Effects Physics
€
∂Nk
∂t= −(V • ∇N )k −
∂ρ ′ w ′ N
ρ∂z
⎛
⎝ ⎜
⎞
⎠ ⎟k
+ Sk − Ak −Ck − Ek
Nk = droplet number mixing ratio in layer k
Ak = droplet loss by autoconversion of droplets
Ck = droplet loss by collection by precipitation
Ek = droplet loss by evaporation
Sk = droplet nucleation source in layer k
f = cloud fraction
w = updraft velocity
Nn = number nucleated (parameterized in terms of w and aerosol)
p(w) = probability density function of w
w* = σw= characteristic updraft velocity in growing part of cloud
€
reff = β3ql
4πρ wN
⎛
⎝ ⎜
⎞
⎠ ⎟
13
2nd IE: Autoconversion connected to droplet number.
€
=max( fk − fk−1,0)
zk+ 1
2− z
k−12
wNnwmin
∞
∫ (w)p(w)dw +∂fk
∂tNn(w*)
1st IE:
CAM and MIRAGE
model version aerosol mass
aerosol number
size distribution
species mixing state
winds
CAM cam3.3.11.tropmz12
prescribed or predicted
diagnosed from mass
prescribed SO4, 2xOC, 2xBC,4xSS, 4xdust, background
external free
MIRAGE CAM2 predicted predicted or diagnosed
variable mode radius
SO4, OC, BC, SS, dust 4 modes
internal within each mode
nudged or free
CAM Aerosol Properties
Aerosol Specie Mode Radius ( m) Geometric Standard Deviation
Hygroscopicity
SO4 0.05 2 0.51 OC 0.02 2.24 0.14, 10-10 BC 0.01 2 10-10 background 0.05 2 0.51 volcanic 0.375 1.25 0.44 sea salt 0.5, 2, 5, 15 1.6, 1.37, 1.4, 1.22 1.3 soil dust 0.2, 3, 15, 30 1.94, 1.3, 1.22, 1.22 0.14
Estimating Direct and Indirect Effects
Two simulations:
1. All aerosol sources
2. All sources except anthropogenic sulfate
Each simulation calculates radiative fluxes with (Faer) and without aerosol (Fnoaer).
Estimating Direct and Indirect Effects
Two simulations:
1. All aerosol sources
2. All sources except anthropogenic sulfate
Each simulation calculates radiative fluxes with (Faer) and without aerosol (Fnoaer).
Direct effect of all aerosol in a simulation is
Fdirect = Faer -Fnoaer.
Estimating Direct and Indirect Effects
Two simulations:
1. All aerosol sources
2. All sources except anthropogenic sulfate
Each simulation calculates radiative fluxes with (Faer) and without aerosol (Fnoaer).
Direct effect of all aerosol in a simulation is
Fdirect = Faer -Fnoaer.
Difference between simulations is . Then
Fdirect = Faer -Fnoaer
Estimating Direct and Indirect Effects
Two simulations:
1. All aerosol sources
2. All sources except anthropogenic sulfate
Each simulation calculates radiative fluxes with (Faer) and without aerosol (Fnoaer).
Direct effect of all aerosol in a simulation is
Fdirect = Faer -Fnoaer.
Difference between simulations is . Then
Fdirect = Faer -Fnoaer
Findirect = Faer -Fdirect
= Fnoaer
IE, DE with 2nd IE CAM tau=0, MIRAGE nudge
First and Second Indirect Effect
-3.5 -3 -2.5 -2 -1.5 -1 -0.5 0
CAM
MIRAGE
Radiative Forcing (W/m2)
Indirect Effect
Direct Effect
No 2nd indirect effectNo Second Indirect Effect
-3.5 -3 -2.5 -2 -1.5 -1 -0.5 0
CAM
MIRAGE
Radiative Forcing (W/m2)
Indirect Effect
Direct Effect
No nudging
No nudging
-3.5 -3 -2.5 -2 -1.5 -1 -0.5 0
CAM
MIRAGE
Radiative Forcing (W/m2)
Indirect Effect
Direct Effect
Change LWP w/, w/o nudging
lwp cam no2ndindir, mirage no2ndindir nudge, mirage no2ndindir
nonudge
Zonal mean IE
Ndrop cam, mirage
Ndrop cam progaer no2ndindir tau=0
Mirage prognaer no2ndindir nudge
Anthro, noanthro
Ccn3 cam, mirage, anthro, noanthro
CCN3 cam progaer no2ndindir tau=0
Mirage prognaer no2ndindir nudge
Anthro, noanthro
Ndrop cam updraft spectrum mirage updraft spectrum
DE, IE cam updraft spectrum
CAM Single vs Spectrum of Updrafts
-4 -3.5 -3 -2.5 -2 -1.5 -1 -0.5 0
single updraft
spectrum
Radiative Forcing (W/m2)
Indirect Effect
Direct Effect
Background aerosol
Background Aerosol
-3.5 -3 -2.5 -2 -1.5 -1 -0.5 0
CAM tau=0
CAM tau=0.01
CAM tau=0.02
MIRAGE
Radiative Forcing (W/m2)
Indirect Effect
Direct Effect
Noanthro ccn3 cam tau=0,0.01, 0.02
Noanthro [CCN3] cam progaer no2ndindir tau=0, 0.01, 0.02
Mirage prognaer no2ndindir nonudge
Sensitivity to size
r=0.05 for oc, bc, volcanic
CAM Sensitivity to Size Distribution
-4 -3.5 -3 -2.5 -2 -1.5 -1 -0.5 0
baseline
rad=0.05
Radiative Forcing (W/m2)
Indirect Effect
Direct Effect
Conclusions
• The much larger indirect effect produced by CAM has not been completely explained.
• The much larger feedback of liquid water path explains at least part of larger indirect effect.
• The larger relative sensitivity of CCN to emissions in CAM may also contribute.
• The CAM CCN and IE are insensitive to the size distribution of OC and volcanic.
• A background aerosol reduces the IE from CAM, but cannot be justified.
Future Work
• Resolve differences between CAM and MIRAGE: insert monthly mean aerosol from each model into simulations by the other.
• Add detrainment of droplet number from cumulus.• Integrate with UW turbulence and shallow cumulus
schemes.• Couple with MIRAGE treatment of aerosol dynamics and
mixing state.• Add nucleation scavenging and size-dependent impaction
scavenging.• Size and composition dependent optical properties.• Add primary and secondary marine organic emissions.