1. Precipitation and albedo variability in marine low clouds
Robert Wood
Duli Chand, Tad Anderson, Louise Leahy, Jayson Stemmler,
Robert J Charlson, Terry Kubar, Dennis Hartmann
University of Washington

2. Cloud cover and albedo
monthly means, Bender et al. (2009)
Mean albedo α and cloud cover fc remarkably linear
 near-constancy of mean cloud albedo αcloud

3. Chand et al. Nature Geosciences (2009)
Practical uses.....
Chand et al. Nature Geosciences (2009)

4. Near-constant mean cloud albedo remarkable in the face of significant cloud morphological changes across regions
Near coast
offshore
Far offshore
near coast
probability
LWP

5. The importance of optically thin low clouds
...the MODIS perspective

6. The importance of optically thin low clouds
...the CALIPSO perspective
Continuum region (Charlson et al. 2007) consists primarily of optically thin low cloud
Integrated attenuated backscatter

7. Do low cloud droplet concentrations favor thin clouds?
inconsistent (?) with Jiang, Feingold and Koren, 2009, J. Geophys. Res.

8. Optically thin low cloud associated with precipitation

9. Pockets of Open Cells (POCs)
October 27/28th 2008
POC Lagrangian - BAe-146 & NSF C-130
100 km

10. MODIS 250 m visible imagery
100 km
Ultraclean region
MODIS 250 m visible imagery
Optically thick cell walls
Optically thin
cell centers
10 km
50 km
VOCALS NSF C-130, RF06, October 28, Photo Rob Wood

11. High clouds and blue sky visible
Radar reflectivity
Radar data Dave Leon
Aircraft track
1.5
1.0
0.5
0.0
height [km] km
Liquid water content
High clouds and blue sky visible
Forward camera
Cloud droplet concentration
Downward camera
Mean volume radius of cloud drops
Ocean surface visible
VOCALS C-130 Flight RF06 in pocket of open cells

12. GOES cloud effective radius (Minnis)27 23 20 18 16 14 12 10 8 6
Visible imagery (MODIS)

13. Ultra-clean layer (UCL)
Accumulation mode
MBL top
All particles
aerosol-depleted
layer
Cumulus cloud
Drizzle scavenging critical for understanding aerosol properties in remote marine boundary layer

14. Precipitation and cloud optical depth
SE Pacific
70-110oW, 40oS-0oS
dBZ Precip L.Heat
[mm day-1] [W m-2]

15. Precipitation drives cloud mesoscale dynamics
Results from EPIC/VOCALS cruises (Bretherton et al. 2004, Wood et al. 2009)

16. without drizzle with drizzle
Savic-Jovcic and Stevens (2007)

17. Aerosols, Clouds and Drizzle
MODIS CloudSat
Smelter
locations
Pollution
Dave Leon
U Wyoming
Leon et al. J. Geophys. Res. (2009)

18. CloudSat: colors Model: lines
Reflectivity
in [LWP, Nd]
space
Kubar et al. (2009, JAS)
Wood et al. (2009, JAS)
Increasing relative importance of LWP over Nd at high rainrates
CloudSat: colors Model: lines
see also Suzuki and Stephens (2008)

19. Summary Remarkable near-constancy of mean cloud albedo
Optically thin clouds prevalent (explaining the “continuum region”), often precipitating
Precipitation rule rather than exception in low clouds
Precipitation in low clouds sensitive to both cloud macrophysics (LWP) and microphysics (Nd).....
.....but as precip increases sensitivity to Nd weakens

21. Droplet conc, LWC variability, drizzle
300
250
200
150
100 50 1
0.1
0.01
10-3
10-4
10-5
Drizzle LWC
Cloud drop conc.
0.2
0.15
0.1
0.05
Longitude [deg W]
Std. dev of cloud LWC
Drop conc. smaller offshore
Clouds more variable offshore
Drizzle greater offshore
Longitude [deg W]

22. Conceptual model of POC edge
Cumulus-coupled MBL Well-mixed MBL
Ultra-clean
[CN = cm-3, CCN = 5-20 cm-3]
Clean
[CN = cm-3, CCN = 100 cm-3]

23. POC formation
Wood et al., 2008, J. Geophys. Res.

25. Cloud liquid water path (minnis)

26. Minimum values assumed in GCMs
Distributions, for all VOCALS flights, of cloud droplet concentration (left) and droplet volume radius (right) for low (black), intermediate (blue) and high (red) liquid water content (qL), for coastal regions east of 77.5oW (top) and remote regions west of 77.5oW. Results show that in coastal regions east of 77.5oW cloud droplet growth is as expected from quasi-adiabatic growth, with droplet concentration approximately independent of liquid water content, and with droplet size increasing with qL. However, in remote regions, there is a population of extremely low cloud droplet concentration. These clouds are primarily found in clouds with low liquid water content. Interestingly, it is these low liquid water clouds that have the largest cloud drop sizes. This behavior is quite different from the behavior seen in the coastal clouds.
Minimum values assumed in GCMs