1. Remote sensing of Stratocumulus using radar/lidar synergy Ewan O’Connor, Anthony Illingworth & Robin Hogan University of Reading

2. Importance of Stratocumulus Most common cloud type globally Global coverage 26% –Ocean 34% –Land 18% Average net radiative effect is about –65 W m -2 Cooling effect on climate

3. Role of drizzle Ubiquitous in clouds deeper than 300m Determines cloud lifetime and evolution Alters droplet spectra Implications for the processing of aerosol particles Feedback on BL dynamics through evaporative cooling

4. Algorithm Assume gamma distribution of the form Radar reflectivity, Z Lidar backscatter  extinction coefficient (    ) Ratio of Z to  gives first guess of D 0

5. Algorithm Doppler spectral width,  v   and improved D 0 D 0 and  v  V T, Z-weighted terminal fall velocity Air velocity, w (+ve upwards) LWC and LWF

6. Observations Lidar backscatter Radar reflectivity

7. Observations Doppler spectral width Doppler velocity

8. Observations Lidar backscatter Radar Reflectivity

9. Derived Parameters Median Diameter Shape parameter

10. Derived Parameters Liquid Water Flux Liquid Water Content

11. Derived Parameters Droplet fall velocity Air velocity

12. Cellular Structure

13. Observations Lidar backscatter Radar reflectivity

14. Observations Doppler spectral width Doppler velocity

15. Derived Parameters Median Diameter Shape parameter

16. Derived Parameters Liquid Water Flux Liquid Water Content

17. Derived Parameters Droplet fall velocity Air velocity

18. Technique 3: Doppler spectra Can use Doppler spectra to infer vertical air velocity, w, since small cloud droplets act as tracers (4 cm s -1 ) Shows cellular nature of updrafts and downdrafts

19. Technique 3: Doppler spectra Identify cloud mode and drizzle mode - determine w Infer Z of drizzle mode and cloud mode w from cloud mode

20. Doppler spectra Drizzle droplets have significant terminal velocities (>1 m s -1 ) Much higher reflectivity since Z = ND 6

21. Doppler spectra Can use spectral and drizzle techniques to obtain w in cloud and below cloud in drizzle

22. Doppler spectra Can use spectral and drizzle techniques to obtain w in cloud and below cloud in drizzle

23. Doppler spectra Can use spectral and drizzle techniques to obtain w in cloud and below cloud in drizzle

24. Conclusion Can infer droplet number concentration in Sc Drizzle drop spectra and liquid water content/fluxes Dynamic motions/overturning in Sc Consistency shown between w derived in drizzle and obtained from Doppler spectra CloudNet – 3 years, 3 sites with radar and lidar

25. Chilbolton observations Sc present 26% of the time 50% of Sc seen by radar contains drizzle droplets

26. Observations

28. Derived Parameters

31. Drizzle flux versus radar reflectivity calculated from ASTEX spectra calculated from FSSP and 2DC size spectra measured by the Met Office C-130 during the Atlantic Stratocumulus Transition Experiment (ASTEX)

32. Spaceborne radar Global values of liquid water flux from a Z/LWF relationship suitable for 94GHz radar LWF (g m -2 s -1 ) = 0.0093 Z 0.69 (mm -6 m -3 )