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)

Clouds types, SST and wind stress in the East Pacific

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

EPIC Sc cruise 9-24 Oct. 2001

Radiosonde observations q qv Cloud base Sharp PBL inversion At Buoy Figure by Kim Comstock

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

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

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

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

Drizzle + solar decoupling? Strong TKE source in cloud Solar Evaporating drizzle suppresses TKE below cloud Drizzle height [m] 2 5 8 11 14 17 20 23 Local time Buoyancy flux

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

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

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

CLOUDSAT VS SURFACE MMCR VIEW OF DRIZZLE

Cloud base and surface rainrates during EPIC – importance of evaporation

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

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

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.