Potential alteration of ice clouds by aircraft soot
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Potential alteration of ice clouds by aircraft soot Joyce E. Penner and Xiaohong Liu Department of Atmospheric, Oceanic and Space Sciences University of Michigan Aviation, Atmosphere and Climate 30 June - 3 July 2003 Friedrichshafen, Germany
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Potential alteration of ice clouds by aircraft soot. Joyce E. Penner and Xiaohong Liu Department of Atmospheric, Oceanic and Space Sciences University of Michigan Aviation, Atmosphere and Climate 30 June - 3 July 2003 Friedrichshafen, Germany. - PowerPoint PPT Presentation
Transcript of Potential alteration of ice clouds by aircraft soot
Potential alteration of ice clouds by aircraft soot
Joyce E. Penner and Xiaohong LiuDepartment of Atmospheric, Oceanic and Space Sciences
University of Michigan
Aviation, Atmosphere and Climate
30 June - 3 July 2003
Friedrichshafen, Germany
Evidence for alteration of ice clouds by aircraft emissions
• Soot associated with increasing ice concentrations in regions of enhanced soot most probably due to aircraft (Ström and Ohlsson, 1998)
• Trend difference in high clouds observed over regions with Computed Contrail cover > 0.5% was 3.5%/decade (land) and 1.6%/decade (ocean) between 1984 and1990 (ISCCP data) (Fahey and Schumann et al. (2001))
• Model results:– Jensen and Toon [1997]– Lohmann [2000]
Mechanisms forming ice clouds
• Homogeneous nucleation– Jhaze = Jw(Teff); Teff= T+Tm
• Deposition nucleation– Js
’=(42rN2Zse)/(2ln(kT))1/2ag
2cl,sexp[-Fg,S/kT]– Fg,S=[16Mw
2i/v3]/[3(RTiln Sv,i)2]f(mi,v,x); mi,v =0.9
– or: Meyer’s empirical formulation: • Nid=exp{a+b[100(RHi-1]}
• Immersion nucleation– Js
’=(42rN2kT)/(h) c1,S exp[-g*/(RT)-Fg,S/(kT)]
– Fg.S=[16Mw2i/v
3]/(3[Lm,0i ln (T0/Te)]2) f(mi,w,x); mi,w =0.5
• Contact nucleation
Warm case (w=4 cm/s)
0
200
400
600
800
0.001 0.01 0.1 1 10 100
Ni (1/cc)
z (m
)
hf only
hf+deposition
hf+immersion
Warm case (w=20 cm/s)
0
200
400
600
800
0.001 0.01 0.1 1 10 100
Ni (1/cc)
z (m
)
hf only
hf+deposition
hf+immersion
Warm case (w=100 cm/s)
0
200
400
600
800
0.001 0.01 0.1 1 10 100
Ni (1/cc)
z (m
)
hf only
hf+deposition
hf+immersion
Cold case (w=4 cm/s)
0
200
400
600
800
0.001 0.01 0.1 1 10 100
Ni (1/cc)
z (m
)
hf only
hf+deposition
hf+immersion
Cold case (w=20 cm/s)
0
200
400
600
800
0.001 0.01 0.1 1 10 100
Ni (1/cc)
z (m
)
hf only
hf+deposition
hf+immersion
Cold case (w=100 cm/s)
0
200
400
600
800
0.001 0.01 0.1 1 10 100
Ni (1/cc)
z (m
)
hf only
hf+deposition
hf+immersion
Parameterization for homogeneous ice formation
• T ≥ 6.07 ln w - 55.0 (fast growth; high T low w):
– Ni=min{exp(a2+b2T+c2lnw)Naa1+b1T+c1lnw , Na}
• T<6.07 ln w - 55.0 (slow growth; low T high w):
– Ni=min{exp(a4+(b4+b5lnw) T+c4lnw)Naa3+b3T+c3lnw , Na}
Homogeneous + deposition nucleation
• Lower updraft velocities and higher temperatures=> deposition nucleation only:– Threshold: T 14.387 ln(w) - 18.825; and w 0.3
m/s
– Si (%) = a T + b;
– where a and b are a function of w
– Use with Meyer’s (1992) parameterization
• Use homogeneous parameterization at higher updrafts and lower temperatures
Homogeneous, deposition, and immersion freezing
• Threshold temperature for immersion, deposition freezing: – T a ln(w) + b– a, b are functions of the number of soot particles Ns
• Immersion freezing:– Ni,s=min{exp(a22)Ns
b22exp(bT)wc, Ns}– b, c are functions of ln Ns
• Deposition freezing:– Maximum supersaturation; Si
max(%) = A T2 + BT + C – A, B, C are functions of w– Number of ice crystals from Meyer’s (1992) parameterization for deposition
• Use homogeneous parameterization at lower T
Immersion nucleation: ice crystal number
0.001
0.01
0.1
1
10
100
0.001 0.01 0.1 1 10
Total soot concentration (cm-3)
Ice
nu
me
r co
nce
ntr
atio
n (
cm-3
)
W=0.5 m s-1
W=-0.04 m s-1
= -60C
= -40C
Sulphate = 200 cm-3
Homogeneous nucleation: ice crystal number
w = 0.04 m s -1
0.01
0.1
1
10
Ice
cry
sta
l nu
mb
er
de
nsi
ty (
cm-3
)
229.3 K214.2 K194.1 K
w = 1.0 m s-1
1
10
100
1000
10 100 1000Total sulfate aerosol concentration (cm -3)
Ice
crys
tal n
umbe
r de
nsity
(cm
-3)
229.3 K214.2 K194.1 K
T=-80C
T=-60C
T=-40CT=-40C
T=-60C
T=-80C
W=0.04 m s-1 W=1.0 m s-1
10 100 1000
Sulfate aerosol concentration (cm-3)
Sulfate aerosol concentration (cm-3)
IMPACT/DAO
• Uses NASA DAO 1997 meteorological fields
• Uses IPCC-recommended emissions inventories except for dust (from Ginoux for 1997 DAO winds)
• Emissions put into BL for dust and biomass burning
• Wet scavenging as in Harvard GEOS-CHEM model except that large scale scavenging uses 0.5 g/m3 for LWC
• Dry deposition as in Zhang, Gong et al. [AE, 2001]
Unique features
• DAO version has improved LWC for sulfate chemistry
• GMI model is based on IMPACT
• We can compare these results with more than one set of meteorological fields:
– IMPACT/DAO=GMI/DAO– GMI/MACCCM3– GMI/GISSII’
Comparison of burdens: GMI models for 1995 ff BC
Burden wet dry Lifetime (Tg) (Tg/yr) (Tg/yr) (days)
DAO 0.058 7.17 1.75 2.40
GISS 0.080 6.92 2.04 3.26
NCAR 0.060 7.31 1.88 2.4
GRANTOUR/CCM1 ffBC+bbBC:0.20 9.56 2.66 5.97
DAO* 0.14 5.00 1.65 7.52
GISSDAO
NCARFuel tracer: ng/g
BC Burdens:DAO 3.3e-4 TgGISS 5.7e-4 TgNCAR 4.1e-4 Tg
Zonal mean SO4 number concentration (cm-3)
Zonal mean ice number (cm-3), homogeneous nucleation only
Relative humidity wrt water (%)
Zonal mean soot number concentration (cm-3)
Zonal mean ice number (cm-3), heterogeneous + homogeneous nucleation, surface sources
Difference in ice concentration between heterogeneous + homogeneous and homogeneous only (cm-3), surface sources
Concentration of soot from aircraft (cm-3)
Concentration of ice (cm-3)
Aircraft + surface sources Surface aerosol sources
Difference in ice concentration between surface + aircraft aerosol sources and surface only sources (cm-3)
Conclusion
• An initial assessment of the potential impact of aircraft emissions on ice concentrations indicates significant increases (O˜100%) in zonal mean concentrations near flight corridors
• Better quantification requires a better simulation of upper tropospheric humidity together with full representation of all aerosol types and their mode of nucleation
