Post on 27-Jan-2016
description
Cloud Processing: Past Work and Issues to Address
Mary Barth
National Center for Atmospheric ResearchMesoscale and Microscale Meteorology
andAtmospheric Chemistry Divisions
transport
washout and rainout
NO production from lightning
How clouds affect chemical species
high photolysis rates
low photolysis rates
cloud chemistry
ice chemistry
cloud microphysics and chemical species
size
phase
transport
How clouds affect chemical species
Transport
Cloud Scale: Given good input data, cloud-scale models simulate transport of passive tracers well. For example:
0 50 100 150 200
12
10
8
6
4
2
Data from STERAO-Deep Convection 1996 (Dye et al., 2000)
Transport
Cloud Scale: Skamarock et al. (2000) simulated with a 3-d cloud model the tracer transport well
Transport
Cloud Scale: Chatfield and Crutzen (1984)Dickerson et al. (1987) Scala et al. (1990, 1993)Pickering et al. (1992a,b)Thompson et al. (1994) Wang and Chang (1993a-d)Wang and Crutzen (1995)Hauf et al. (1995)And many others
TransportLarge Scale: A much bigger challenge, particularly for subgrid convection
Mass flux schemesEmmanuel (1991), Feichter and Crutzen (1990), Hack (1994),
Tiedtke (1989), Zhang and McFarlane (1995), and others
Mass flux + convective-scale w + mesoscale effectsDonner et al. (2001)
“superparameterization” 2-d cloud resolving model used as convective transport
parameterizationGrabowski (2001)Khairoutdinov and Randall (2001)
Mass flux + convective-scale w + mesoscale effectsDonner et al. (2001)
“superparameterization”Khairoutdinov and Randall (2001)
CCSM/CRM
CCSM
Obs.
How can we improve convective transport of chemical constituents in large-scale models?
CRMs need to generalize their results
Can we use several CRMs with chemistry in concert to analyze convective transport for all different types of convection? Could the results be brought together to produce general characteristics of tracer transport?
Should superparameterizations include simple cloud chemistry?
Effort to verify model results with observations
washout and rainout
How clouds affect chemical species
Wet DepositionResolved Clouds:Precipitation rate = Vr qr
where r = air density Vr = fall speed of rain qr = mixing ratio of rain
Wet deposition rate = Vr Cr
where Cr = mixing ratio of species in rain
If Cr is not predicted in the model,usually Henry’s law is used:
Cr = KH R T LWC Cg
where KH = Henry’s law coefficient (mol/L-atm) R (L-atm/mol-K), T (K), LWC (cm3 H2O/cm3 air), Cg = gas-phase mixing ratio
Is the Henry’s law assumption valid?
This assumption depends on the time step and Henry’s law coefficient
HNO3
NH3
H2O2
25 m
20 m
15 m
10 m 5 m
T=10°C
2000
1000
500
r=25 m
r=10 m
T=30°C 20°C 10°C
H2O2
100
1000
1e5 3.5e5
1e4 1e6 1e8 1e10 1e12
Wet Deposition
Large-scale Models
Wabove
Win = qr_prod KH* Cgas
Wbelow = Wabove + Win
W_below_cloud = (Pr – E) KH* Cgas
qr_prod = conversion from CW to rain, Pr = precip. Rate, E= evaporation rate
Giorgio and Chameides (1986)Wetdep = - Cgas where = Q F Tc L
Flux Method 1 (Barth et al., 2000; Roelofs and Lelieveld, 1995)
More physically correct, but still is not great
Wet Deposition
Subgrid-scale Clouds
Wabove
Win = (qr_prod – E) KH* Cgas
Wbelow = Wabove + Win
qr_prod = conversion from CW to rain, E= evaporation rate
Flux Method 2 (work in progress, Hess et al.)
This is even more physically correct, but still needs work:
MOZART, Giorgi and Chameides (1986) wet deposition
MOZART, Flux Method 2 wet deposition
Observations
He
igh
t (km
)
Wet Deposition: Needs
Wet deposition depends on both the precipitation rate and the concentration of the species in the precipitation. Do we get the precipitation rate right? If not, what are we missing? – Small cumulus: giant aerosols that form large
cloud drops that initiate formation of rain– Deep convection: ice processes
Verification of what parameterizations work or not– Comparisons of nitrate wet deposition model vs.
observations (Holland et al.)– Comparisons of wet deposition from global-scale
models with cloud-scale models
How clouds affect chemical species
cloud chemistry
ice chemistry
Cloud Chemistry
Aqueous-phase Chemical Reactions
Modification of Gas-phase Chemistry because Reactants are Separated
Examples:
SO2
H2O2
S(IV)
H2O2
SO4=
Aqueous Chemistry
Separation of Species
OHNONOHO 22
HO2 + O2-
Simulated Sulfate BudgetSource: Roelofs et al., 2001; Rasch et al., 2000
-100
-80
-60
-40
-20
0
20
40
60
80
100
DJF JJA DJF JJA DJF JJA Annual
Emissions
Gas Chemistry
AqueousChemistryDry Deposition
Wet Deposition
E. N. America Europe SE Asia Global
E. North America Europe SE Asia Global
Pe
rce
nta
ge
of T
ota
l Pro
du
ctio
n o
r D
est
ruct
ion
Ra
te
Rates of S(IV) aqueous reactions
SO3= + O3
HSO3- + O3
HSO3- + H2O2
pH
Rat
e of
Rea
ctio
n (M
s-1)
SO2 = 2 ppbvH2O2 = 1 ppbvO3 = 50 ppbv
Aqueous Sulfur Chemistry Needs
• Representing S(IV) S(VI) conversion seems to be pretty well in hand.
• Minor – Major Improvements:– Importance of representing size and therefore pH
of drops better (more on this later)– Importance of getting the LWC correct– Conversion via other reactions e.g. transition
metal ion chemistry
Does Cloud Chemistry Affect O3 Concentrations?
Lelieveld and Crutzen (1991)
“Clouds thus directly reduce the concentrations of O3, CH2O, NOx and HOx”
Liang and Jacob (1997)
“It is found that the maximum perturbation to O3 from cloud chemistry in the tropics and midlatitudes summer is less than 3%”
Does Cloud Chemistry Affect O3 Concentrations?
Walcek, Yuan, and Stockwell (1997)
“… in-cloud reactions strongly influence local O3 production in polluted areas, but longer-term impacts of clouds on O3 formation would be much smaller due to compensating chemical processes in regions remote from NOx emissions.”
Barth, Hess, and Madronich (2002) find that O3 is depleted via cloud chemistry by a small amount at low pH and by a more significant amount at high pH. Further, the effect of cloud on photolysis rates can contribute to O3 depletion.
Percent Change in Ozone for a Cloud-topped Marine Boundary Layer (z<2 km) near Hawaii (regional
chemistry transport model results)
pH = 4.0 pH = 4.5 pH = 5.0 pH = 5.5
O3 -3.0 -6.1 -10.8 -16.9
Percent Change in Ozone with the Effect of Clouds on Photolysis vs. without the Effect on Photolysis
pH = 4.5No cloud correction on j-values
With cloud correction on j-values
O3 -3.0 -6.1
Spatially Averaged, Diurnally Averaged O3 Production and Loss Rates
gas pH=4.0 pH=4.5 pH=5.0 pH=5.5
NO + HO2 244 162 152 145 142
NO + CH3OO 288 306 312 317 322
O3 + h 4211 4094 3970 3774 3508
O3 + HO2 509 323 286 257 232
O3 + OH 227 212 203 189 171
O3 + O2- 0 402 710 1163 1741
Units are pptv/day
Does Cloud Chemistry Affect O3 Concentrations?
Cloud Chemistry (aqueous chemistry + separation of reactants) may not have a big effect on O3 concentrations by itself, but the sum of the cloud effects (cloud chem., radiation, scavenging, etc.) may perturb O3 “substantially”.
What are the key parameters for calculating cloud chemistry?
Liquid Water Content
The size of the drops(more on this later)
Is the question, “Does cloud chemistry alter O3 concentrations?”, dead?
• NO! Because there are so many things to consider with ozone chemistry.– More accurate depiction of clouds– Many situations where the chemistry is much more
complex, e.g. cloud-topped boundary layers with nearby hydrocarbon and NOx emissions
– Volatile organic compounds participation will then need to be assessed Organic Aqueous Chemistry
How clouds affect chemical species
cloud microphysics and chemical species
size
phase
Microphysics and Chemistry
Cloud Drop Activation
Collision/CoalescenceCondensation
FreezingRimingMelting
Representing Cloud Physics in Large-scale Models
Represent cloud drops as one reservoir, rain as another reservoir, and ice and snow as separate reservoirs. This is termed bulk-water microphysics.
Cloud water
Water vapor
Ice
Rain Snow
Representing Cloud Physics in Parcel Models
Cloud Drop Activation
Cloud chemistrySO2 SO4
Collision/CoalescenceCondensation
Represent aerosols, cloud drops, and rain drops using size bins
Parcel model results should be closer to the truth
?
Simulating Size-Varying Cloud Drop Population vs. Cloud Water with a Mean Radius
• Hegg and Larson (1990) condensational growth only
• Roelofs (1993) condensation and collision/coalescence
• Gurciullo and Pandis (1997) condensational growth only
• Kreidenweis et al. (2003) condensational growth only; intercomparison of 7 aerosol parcel models
Sulfate Production from Explicit Models vs. Bulk-Water Models
SO2 (ppbv)
H2O2 (ppbv)
Bulk (ppbv)
Explicit (ppbv)
E/B Reference
2.0 0.5 0.72 0.54 0.8 Hegg and Larson, 1990
0.2 0.5 0.08 0.18 2.1 Hegg and Larson, 1990
4.0 0.5 6.0 7.5 1.25 Roelofs, 1993
1.0 0.5 2.4 4.1 1.7 Roelofs, 1993
4.0 1.0 9.4 10.1 1.07 Roelofs, 1993
10.0 0.5 0.62 0.81 1.29 Gurciullo and Pandis, 97
0.25 0.5 0.20 0.24 1.21 Gurciullo and Pandis, 97
0.2 0.5 .145 .172 1.18 Kreidenweis et al., 2003
mol/L
Why is there more sulfate production with explicit microphysics?
pH varies across the droplet spectrum
Observations have shown that the chemical composition varies with the size of the cloud drop
Noone et al. (1988), Ogren et al. (1989, 1992)Munger et al. (1989), Collett et al. (1993, 1994)
Percent Change in Ozone for a Cloud-topped Marine Boundary Layer (z<2 km) near Hawaii (regional
chemistry transport model results)
pH = 4.0 pH = 4.5 pH = 5.0 pH = 5.5
O3 -3.0 -6.1 -10.8 -16.9
Is there an important effect of drop size (pH variability) on cloud photochemistry?
Microphysics and Chemistry
Cloud Drop Activation
Collision/CoalescenceCondensation
FreezingRimingMelting
Microphysics and Chemistry
?
?
?
drop liquidin amount t Constituen
particlefrozen in amount t Constituen Factor Retention
Snow Accreting Cloud Water (riming)
Retention Factor Reference
SO2 0.25 Iribarne et al., 1983
0.012 + 0.0058 TLamb and Blumenstein, 1987
0.25 + 0.012 T Iribarne et al., 1990
0.62 (ventilated) Iribarne et al., 1990
0.34 to 0.83 Iribarne and Barrie, 1995
0.02 Voisin et al., 2000
T = 0 – T (ºC)
H2O2 1.0Iribarne and Pyshov, 1990
0.07 to 0.56 Snider et al., 1992
0.01 to 0.36 Snider and Huang, 1998
Test the Importance of Retaining Gas Species in Frozen Hydrometeors
Convective Cloud Model coupled with Gas and Aqueous Phase Chemistry
Simulate a storm that was observed in northeastern Colorado (Dye et al., 2000) Evaluate how well the model represents observed
convection Evaluate passive tracer transport Skamarock et al. (2000)
Convective Cloud Simulation
Hydrometeor Mixing Ratios
Barth et al. (2001)
SO2 and H2O2 in outflow region
Barth et al. (2000)
Yin et al. (2002) used a 2-d axisymmetric cloud model to investigate retention during riming and adsorption.
Crutzen and Lawrence (2000) found the mixing ratio of trace gases with KH = 103, 104, 105 M/atm reduced in the middle to upper troposphere by 20%, 60%, 90% from global model calculations.
KH
0102
103
104
105
M/atm
Microphysics and Chemistry
Size of drops is important to cloud chemistry
Phase of cloud is important to cloud chemistry (generally aqueous chemistry does not happen in ice) and scavenging (wet deposition).
Ice chemistry
HNO3 iceNO3
- + h NO2
Heterogeneous Chlorine chemistry, e.g.:HCl + ClONO2 Cl2 + HNO3
Other chemistry?
How clouds affect chemical species
high photolysis rates
low photolysis rates
Radiative Effects on Photolysis Rates
Matthijsen et al. (1998)
ACE-1 observations and modeling
O3 + h O('D) + O2 photodissociation rate
jO3jO3
jO3 jO3
Radiative Effects on OH concentration
Matthijsen et al. (1998)
ACE-1 observations and modeling
+ observed OH modeled OH
Monte Carlo simulations to calculate photodissociation rates in the presence of cumulonimbus. Brasseur, A.-L. et al. (2002)
J-CH2O
Radiative Effects on Photolysis Rates
Online calculations of photodissociation rates this allows consistent calculation of j-values with environmental conditions, e.g. clouds and aerosols
Landgraf and Crutzen (1998)Blan and Prather (2002)Tie et al., in preparation
Landgraf and Crutzen (1998)
Cloud
Cloud
Issues regarding the Radiative Effect of Clouds
• How important are ensembles of cumulus clouds which produce lots of scattering (multiple reflections) to the sides of clouds?
• How important are absorbing aerosols within the cloud?
NO production from lightning
How clouds affect chemical species
Lightning-produced NOx global estimates
REFERENCE(type of estimate)
P(NO)(1016 molecules
J-1)
P(NO)(1025
molecules flash-1)
F(102 flashes s-1)
G(NO)(Tg (N) year-1)
Lawrence et al. (1995) (review)
- 2.3 (1 – 7) 1 ( 0.7 – 1.5) 2 (1 – 8)
Price et al. (1997) (obs)
10 - 0.7 – 1 12.2 (5 – 20)
Price et al. (1997) (theor.)
10 - - 13.2 (5 – 25)
Wang et al. (1998) (lab)
- 3.1 0.3 – 1 2.5 – 8.3
Nesbitt et al. (2000) (satellite)
- 0.87 – 6.2 0.57 0.9
Skamarock et al. (2003) (obs/mdl)
- 2.6 0.001 – 0.009* -
Skamarock et al. (2003)
Skamarock et al. (2003)Defer et al. (in review)
Allen and Pickering (2003)
OTD data
Mass Flux estimate
Convec. Precip. estimate
Cloud Height estimate
Allen and Pickering (2003)
Calculations of Effect of Lightning on ChemistryHauglustaine et al. (2001)
Issues on Parameterizing Lightning-Produced NOx
• Knowing the number of thunderstorms occurring on the earth over a year
• Parameterizations based on characteristics of individual storms: Deep convection comes in several different flavors
• Verification of the parameterizations with observations
Some Issues to Address
Vertical TransportCoupling CRMs and global modelsSuperparameterizationsVerification
LightningCoupling small scale to global scale modelsVerification
MicrophysicsVerification of cloud volume, precipitation, phase, LWC
Coupling the climate, cloud, aerosol, chemistry system