1. Inhomogeneous radiative properties of cirrus clouds
(Photo courtesy of
Steven Dobbie, University of Leeds
Reading, Dec 8

2. Clouds in GCMs Diagnostic Prognostic ice/liquid water content
‘Statistical’ Prognostic schemes (eg Tompkins 2002).
Plane parallel homogeneous (PPH) clouds introduce bias (Cahalan 1994, Barker et al 1998 and Larson et al 2001)

3. Motivation Climate is very sensitive to cirrus
Cirrus are poorly understood (GCSS WG2)
Inhomogeneity and radiative properties

4. Motivation Observed cloud structure (1, 2-3, 5 km)
Smith and Jonas, ‘96, ‘97
Quante et al., ‘96
Demoz et al., ‘96
Gultepe and Starr, ‘95
Starr et al., ‘92
Starr and Cox, ‘85
GCM sub-grid inhomogeneity treatment

5. The Large Eddy Model The LEM: 2D mode (100 km domain)
100 m horizontal resolution, 125 m vertical resolution
3 phase microphysics with dual moment ice/snow
Rigid top and bottom
Periodic lateral boundary conditions
Fu-Liou radiation model

6. Initial Profiles
UK LES CRM

7. IWC Time Evolution

8. Cellular Development

9. Length-scales of inhomogeneity

10. Inhomogeneity and Cloud Depth

11. Spectral Dependence

12. Radiative Heating Profiles

13. Cloud Lifetime

14. Radiation and Latent Stability Numbers

15. Instability (Rad. Influenced)

16. Instability (No Rad.)

17. Previous studies
Wide range of results between cirrus models even for simple idealised case studies (Starr et al 2000).
There are few comparisons of CRM results with observations for ice clouds. In existing comparisons modelled inhomogeneity can be much less than observed (eg Benedetti and Stephens 2001)

18. Observed and LEM profiles

19. Ice Water Contents (IWCs)
Radar
LEM
Approx km

20. Effects of shear on sub-grid variability
9.25 km
8.25 km
Orange is with shear, Black is without (all are over 50 km in the horizontal and 375 m in the vertical).
Ice water content
Total Water Content

21. Effect of shear on vertical correlation of IWC

22. Motivation
Question: By neglecting 3D radiative transfer, are we missing an important influence on cloud evolution or can it be neglected?

23. PPA and ICA/IPA Radiaton

24. Monte Carlo Radiation

25. Radiative smoothing scale

27. Inhomogeneous cirrus layersMC
IPA

28. Inhomogeneous cirrus layers
Rmc=0.219
R4s=0.225
Rnr=0.196

29. Inhomogeneous cirrus layers

30. Finite cirrus layer MC
IPA

31. Finite cirrus layer Rmc=0.423 R4s=0.396 Rnr=0.372

32. Finite cirrus layer

33. Summary/Conclusions Radiative effects are important for cirrus
Inhomogeneous stratiform layers: 2-3%
Finite, inhomogeneous cirrus clouds: 6-7%

34. Further Work
Realistic clouds (Chilbolton,FIREII, Emerald1, Crystal Face)
with various geometries
Longer duration simulations
Quantify effects on cloud microphysics
Effect for PDFs?
Understand 3D radiation in presence of other effects, like shear
Other cloud types

35. [G. Heymsfield]
Tropical Anvils

38. Inhomogeneous layer

39. Finite cirrus layer

40. 16 July C-F Anvil Mission P. Lawson D. Baumgardner A. Heymsfield

41. Observations:. Supersaturation Frequently Observed in the Upper
Observations: Supersaturation Frequently Observed in the Upper Troposphere
[J. Smith, A. Anderson, P. Bui]
We observe supersaturation both in clear air and in the presence of cirrus.

42. Observed and LEM profiles
Reading, Dec 8

43. Microphysics

44. Effects of shear on sub-grid variability
9.25 km
8.25 km
Orange is with shear, Black is without (all are over 50 km in the horizontal and 375 m in the vertical).
Ice water content
Total Water Content

45. Effects of shear on sub-grid variability
6.5 km
4.7 km
Orange is with shear, Black is without (all are over 50 km in the horizontal and 375 m in the vertical).
Ice water content
Total Water Content

46. Effect of shear on vertical correlation of IWC

47. Conclusions Further Work
Distributions of modelled IWCs and total water contents are well described by beta functions.
Shear tends to decrease the variance in IWC and total water contents.
The decorrelation of IWC with height is initially linear (as suggested in Hogan and Illingworth 2002). At larger vertical separations correlations tend to be zero for zero shear and are more complex for inhomogenous clouds with large wind-shears.
Further Work
Improve the initialisation of the LEM.
Study a better observed case (with aircraft observations).
(Acknowledgements: Robin Hogan, Reading University)