1. EPIC 2001 SE Pacific Stratocumulus Cruise 9-24 October 2001 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. NOAA/ETL (surface met., fluxes, mm radar, lidar) Participants

5. UNAM (aerosol concentration and characterization)

6. Participants WHOI (CTDs, IMET buoy)

7. Participants University of Washington (sondes, 5 cm scanning radar, meth blue, cloud photos)

8. EPIC Sc cruise 9-24 Oct. 2001

10. Radiosonde observations  qvqv Cloud baseSharp PBL inversion At Buoy Figure by Kim Comstock

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

12. [m s -1 ] ECMWF VERTICAL VELOCITY [dBZ] 10 -10 0 Diurnal Cycle

13. Large scale observations of the diurnal cycle of low cloud (cont.) TRMM TMI (microwave imager) observations of LWP Wood, Bretherton, and Hartmann (2002) SE PACIFIC [85W, 20S], 1999-2000 LOCAL TIME [hr] LWP [g m -2 ] 0 6 12 18 24

14. Geographical variations MEAN LWP AMPLITUDE [fraction] TIME OF MAXIMUM LWP Strongest diurnal cycle of LWP found in the regions of low cloud to the west of continents Larger amplitudes in southern hemisphere Peak LWP at 02-06 hr showing diurnal cycle of insolation is key modulator Summer max. in amplitude 12 6 0 18 12 0.4 0.3 0.2 0.1 0.0 150 100 50 0

15. Diurnal cycle of subsidence w s, entrainment w e, and  z i /  t NIGHT DAY NIGHT DAY wsws wewe dz i /dt  w e = 0.24 cm s -1 ;  w s = 0.26 cm s -1 ;   z i /  t = 0.44 cm s -1  z i /  t + u  z i = w e - w s  0.05 cm s -1

16. Mixed layer budgets Latent Evap zizi Free trop. Mixed layer Sensible Heating qTqT SLSL Precip EntrainmentLWSW Net radiative flux divergence qTqT SLSL Ocean

17. Estimating budget terms LE zizi SHRain Entrainment LWSW Ocean bulk flux algorithm using Ron Brown met measurements 3hr radiosonde profiles, observed LWP and Fu-Liou radiation scheme cloud radar, ECMWF subsidence, + MODIS BL depth climatology cloud radar + microphysical model Advection terms estimated using NCEP and ECMWF reanalyses Storage terms estimated using sonde profiles

18. Solar absorption and drizzle evaporative stabilization zizi Ocean Solar absorption SW Drizzle evaporaton warmingcooling Evaporative cooling

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

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

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

22. Meth Blue Rain Rate Number/second Z=58R 1.1

23. Remotely-sensed cloud microphysics (Rob Wood, UW) …UNAM also found a strong diurnal signal in submicron aerosol conc.

24. MODIS 10/16/2001; 10:00 Local (16:00 UTC) 1 3 10 30 100 300 1000 cm -3 0 50 100 150 200 250 300 g m -2 0 5 10 15 20 25 30 mm Liquid water pathDroplet concentrationEffective radius SHIP 250 km

25. Comparison of 6-day mean 20S 85W profiles with models All models (esp CAM) have too shallow a PBL. CAM2 LWC all in lowest 3 levels (70-630 m). Observed LWC mainly at 800-1300 m. (Peter Caldwell, UW)

26. Conclusions A remarkable dataset was gathered documenting both spatial and diurnal variability of the SE Pacific Sc regime Pronounced diurnal cycle, amplified by subsidence wave from S America. Mesoscale drizzle cells ubiquitous, especially at night; rain mostly evaporates above surface, sensitive to cloud drop conc. Boundary layer deeper than current global models; well-mixed in early evening but near total shut-down of entrainment in early morning due to combination of solar absorption and drizzle evaporation