1. Cloudsat and Drizzle: What can we learn
Cloudsat and Drizzle: What can we learn? Robert Wood, University of Washington, Seattle contributions from Chris Bretherton, Kim Comstock, Sandra Yuter, Peter Caldwell and Bjorn Stevens CLOUDSAT Science Team Meeting, Laguna Beach, May 2004

2. Fraction of precipitation reports indicating “drizzle”
Drizzle is prevalent form of
precip. in MBL cloud regions
0% % % % 40% 50% >50%

3. Precipitation rates by dynamical regime

4. Light precipitation constitutes sizeable fraction of the areal mean rain amount in the tropics and subtropics

5. IMET Buoy (85W, 20S) measurements (data courtesy of Robert Weller, WHOI)

6. Scanning C-band radar (EPIC 2001) drizzle is intermittent with cellular structure max reflectivity of dBZ 0
90
180
270
15 km
30 km
dBZ

7. Can drizzle affect MBL dynamics?

8. Cloud macrostructure
Pockets Of Open Cells (POCs) are frequently observed in otherwise unbroken Sc. These may be formed as a cloud response to drizzle-induced decoupling
POCs

9. Microphysical-macrophysical links
Figure courtesy
Bjorn Stevens, UCLA
0 Tb 5
Low Tb indicative of large drops
m brightness temperature difference

10. More drizzle in heterogeneous clouds
MODIS brightness temperature difference, GOES thermal IR, scanning C-band radar

11. What we know Drizzle is common in the subtropical MBL
Drizzle has the potential to influence cloud dynamics and possibly macro-structure

12. What we don’t know Climatological distribution of drizzle
What factors control the production of drizzle (cloud thickness, LWP, cloud microphysics)
Quantitative assessment of the role of drizzle in modifying cloud dynamics/structure

13. How Cloudsat/A-Train can help
Cloudsat will provide seasonal maps of drizzle in the subtropical MBL
Aqua (MODIS, AMSR-E) and CALIPSO will provide estimates of MBL forcing terms (cloud cover, LWP, microphysics, SST, MBL-depth)

14. Fraction of areal mean precipitation observed

15. How long do we need to average?

16. Cloudsat Validation plans
IMET buoys in regions of light precipitation (SE Pacific, Atlantic trade-winds) – “surface drizzle indicator”
VOCALS 2007 – Ship/aircraft/island-based field campaign in SE Pacific stratus

17. Suggested outline of approach
(a) Produce quantitative seasonal mean maps of drizzle properties in the subtropical MBL using Cloudsat
(b) Use Aqua/Calypso measurements and NCEP/ECMWF reanalysis to constrain MBL forcing terms
(c) Begin holistic synthesis of satellite measurements using new Park/Leovy/Rozendaal MBL model as framework
(d) Make quantitative assessment of the importance of precipitation in forcing the subtropical MBL

18. Mean entrainment rates
Entrainment rate [mm/s] ◄ NE Pacific SE Pacific ► Subsidence rate [mm/s]

19. Can precipitation affect MBL dynamics?
Mixed layer budget analysis using observationally-derived forcings (EPIC 2001) and entrainment, shows subcloud negative buoyancy fluxes ( decoupling) only when drizzle is included

20. Frequency of precipitation occurrence (from Petty 1995)
Fraction of reports indicating some form of precipitation (JJA )
Regions dominated by MBL
cloud do precipitate
0% % % % % %