1. Simple CCN budget in the MBL 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  0

2. Production terms in CCN budget FT Aerosol concentration MBL depth Entrainment rate Wind speed at 10 m Sea-salt parameterization-dependent constant 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 Precip. rate at cloud base MBL depth Constant cloud thickness Wood, J. Geophys. Res., 2006 Comparison against results from stochastic collection equation (SCE) applied to observed size distribution

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) Box-whisker: CCN obs (Snider) 5,10,25,50,75,90,95 th %, triangle=mean cyan = individual spectra Black curve: Weber and McMurry (1996, Mauna Loa, subsiding conditions) Same data, Log scale

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) 5,10,25,50,75,90,95 th %, 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: 350-420, depending on composition RF14: 2000-3000 in plume

8. Model and observed N d

9. With Tony’s size distributions RF03 RF05 Number activating (S=0.3%) Snider (mean/median): 140/120 cm -3 Weber/McMurry: 125 cm -3 RF05: 50-75 cm -3, depend. on comp. RF03: 350-420 cm -3, depend. on comp. RF14: 2000-3000 in plume buffered by sea-salt buffered by precip

10. N d hovmoller MODIS and VOCALS aircraft obs (symbols) Strong coherent synoptic variability, especially west of 80 o W

11. N d histograms for remote region (78-86 o W, 18-22 o S) Mean values: MODIS: 98 cm -3 C-130: 99 cm -3 C-130, q l >0.02 MODIS, f liquid >0.99 skewed tails

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

13. Reduction of N d from precipitation sink 0 10 20 50 100 150 200 300 500 1000 2000 % Precipitation from midlatitude low clouds reduces N d by a factor of 5 In coastal subtropical Sc regions, precip sink is weak

14. Predicted and observed N d Monthly climatological means (2000-2009 for MODIS, 2006-2009 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. Histograms of predicted and observed mean N d [45 o S-45 o N, subsiding regions] Cloud droplet concentration [cm -3 ] dp/dN d MODIS MODEL tail driven by regions of very low precip

16. Histograms of predicted and observed mean N d [45 o S-45 o N, 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 N FT 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 28 th POC case All VOCALS clouds