1. The EPIC 2001 SE Pacific Stratocumulus Cruise: Implications for Cloudsat as a stratocumulus drizzle meter Rob Wood, Chris Bretherton and Sandra Yuter (University of Washington) Chris Fairall, Taneil Uttal (NOAA/ETL) Bob Weller (Woods Hole OI)

2. Clouds types, SST and wind stress in the East Pacific

3. Goals Document cloud and boundary layer structure in the SE Pacific
Assess the importance of drizzle processes to cloud thickness and extent
Compare results with other Sc regimes and with large-scale models
Maintain WHOI IMET buoy at 20S 85W

4. EPIC Sc cruise
9-24 Oct. 2001

6. Radiosonde observationsq qv
Cloud base
Sharp PBL inversion
At Buoy
Figure by Kim Comstock

7. Cloud top and dBZ (MMCR), base (ceilometer), LCL (surf. met.)
cld top
cld base
LCL

8. [m s-1]
ECMWF VERTICAL VELOCITY
Diurnal
Cycle 10
[dBZ]
-10

9. Diurnal cycle of subsidence ws, entrainment we, and zi/t
 0.05 cm s-1
zi/t + u•zi = we - ws
NIGHT DAY NIGHT DAY we
dzi/dt ws
swe=0.24 cm s-1; sws=0.26 cm s-1; szi/t=0.44 cm s-1

10. Solar absorption and drizzle evaporative stabilization
Drizzle evaporaton SW zi
Evaporative cooling
cooling
warming
Ocean

11. Drizzle + solar decoupling?
Strong TKE source in cloud
Solar
Evaporating drizzle
suppresses TKE
below cloud
Drizzle
height [m]
Local time
Buoyancy flux

12. Diurnal cycle of convective velocity scale
Drizzle and solar radiation reduce mean w* by comparable amounts

13. Sample of C-band scanning radar and coincident MMCR
20 km
dBZ
0530
0730

15. Drizzle structural properties: more power at small scales than LWP
UK aircraft data
Drizzle structural properties: more power at small scales than LWP
EPIC MMCR
Typical LWP
scaling

16. CLOUDSAT VS SURFACE MMCR VIEW OF DRIZZLE

17. Cloud base and surface rainrates during EPIC – importance of evaporation

18. Z-R relationships for drizzle – variations below cloud are important

19. Second indirect effect?
…Cloudsat should help to answer these questions…..

20. Conclusions
A remarkable dataset was gathered documenting both spatial and diurnal variability of the SE Pacific Sc regime
Pronounced diurnal cycle, particularly strong drizzle cycle – most drizzle at night.
Mesoscale drizzle cells ubiquitous, especially at night; more variability at small scales than LWP. Rain mostly evaporates above surface, sensitive to cloud drop conc.
Z-R relationships for Sc are different from those in other cloud systems – effect of evaporation important.