1. Simple CCN budget in the MBL
 0
Model accounts for:
Entrainment
Surface production (sea-salt)
Coalescence scavenging
Dry deposition
Model does not account for:
New particle formation – significance still too uncertain to include
Advection – more later

2. Production terms in CCN budget
Entrainment rate
FT Aerosol concentration
MBL depth
Sea-salt
parameterization-dependent
constant
Wind speed at 10 m
We use Clarke et al. (J. Geophys. Res., 2007) at 0.4% supersaturation
to represent an upper limit

3. Loss terms in CCN budget: (1) Coalescence scavenging
Constant
Precip. rate at cloud base
cloud thickness
MBL depth
Comparison against results from stochastic collection equation (SCE) applied to observed size distribution
Wood, J. Geophys. Res., 2006

4. Steady state (equilibrium) CCN concentration

6. Free-tropospheric CCN spectra (West of 75W)
RF03 (high CO west of 80W)
RF05 (low CO west of 84W)
Same data, Log scale
Box-whisker: CCN obs (Snider)
5,10,25,50,75,90,95th %, triangle=mean
cyan = individual spectra
Black curve: Weber and McMurry (1996, Mauna Loa, subsiding conditions)

7. Free-tropospheric CCN spectra (West of 75W)
RF03 (high CO west of 80W)
RF05 (low CO west of 84W)
Box-whisker: CCN obs (Snider)
5,10,25,50,75,90,95th %, triangle=mean
cyan = individual spectra
Black curve: Weber and McMurry (1996, Mauna Loa, subsiding conditions)
Number activating (S=0.3%)
Snider (mean/median): 140/120 cm-3
Weber/McMurry: 125 cm-3
RF05: 50-75, depending on composition
RF03: , depending on composition
RF14: in plume

8. Model and observed Nd

9. With Tony’s size distributions
Number activating (S=0.3%)
Snider (mean/median): 140/120 cm-3
Weber/McMurry: 125 cm-3
RF05: cm-3, depend. on comp.
RF03: cm-3, depend. on comp.
RF14: in plume
With Tony’s size distributions
RF03
RF05
buffered by precip
buffered by sea-salt

10. Nd hovmoller
MODIS and VOCALS aircraft obs (symbols)
Strong coherent synoptic variability, especially west of 80oW

11. Nd histograms for remote region (78-86oW, 18-22oS)
Mean values:
MODIS: 98 cm-3
C-130: 99 cm-3
C-130, ql>0.02
MODIS, fliquid>0.99
skewed tails

12. Mean precipitation rate (CloudSat, 2C-PRECIP-COLUMN, Stratocumulus regions)

13. Reduction of Nd from precipitation sink
Precipitation from midlatitude low clouds reduces Nd by a factor of 5
In coastal subtropical Sc regions, precip sink is weak %

14. Predicted and observed Nd
Monthly climatological means ( for MODIS, for CloudSat)
Derive mean for locations where there are >3 months for which there is:
(1) positive large scale div.
(2) mean cloud top height <4 km
(3) MODIS liquid cloud fraction > 0.4
Use 2C-PRECIP-COLUMN and Z-R where 2C-PRECIP-COLUMN missing

15. tail driven by regions of very low precip
Histograms of predicted and observed mean Nd [45oS-45oN, subsiding regions]
MODIS
MODEL
tail driven by regions of very low precip
dp/dNd
Cloud droplet concentration [cm-3]

16. model cannot explain highest concentrations (near coasts)
Histograms of predicted and observed mean Nd [45oS-45oN, subsiding regions, log scale]
MODIS
MODEL
model cannot explain highest concentrations (near coasts)

17. Sea-salt source strength compared with entrainment from FT

18. POCs and aerosols

19. Steady-state cloud condensation nucleus (CCN) model
Assumptions:
1. Wind-driven sea-salt
production and entrainment of NFT CCN from free-troposphere
are only aerosol sources
2. Coalescence scavenging is the only loss term
3. Examine steady state solution for CCN concentration
VOCALS, Oct 28th POC case
All VOCALS clouds