1. The radiative properties of inhomogeneous cirrus clouds
Steven Dobbie
Sat Ghosh
Leeds
Peter Jonas
UMIST

2. Motivation
Climate - radiative properties and cloud feedbacks, distribution of H2O
Weather – Moisture distribution, precip, surface temperature
Aerosols – distributions and processing
Heterogeneous chemistry
Satellite retrievals

3. Motivation Cirrus cloud structure (1, 2-3, 5, 20 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

4. Clouds in GCMs
Prognostic water schemes

5. More motivation
GCSS WG2 (Starr et al 2000)

6. Emerald case

7. Water Vap Diffusivity

10. Chilbolton case
LEM
10.00
09.00
09.30

12. What effect does 3D radiation
have on the evolution and
radiative properties of cirrus?

13. Research Tools
LEM (cloud model)
MC (3D radiation model)

14. IWC Time Evolution
Rad
No-Rad

15. Scales of inhomogeneity
Rad
No-Rad

16. Spectral Dependence

17. PPA radiative transfer

18. ICA or IPA

19. Monte Carlo radiation

20. Radiative smoothing DZ

21. Inhomogeneity scale

22. Layer simulations MC
IPA

23. Layer simulations
Rmc=0.219
Rppa=0.225

24. Layer simulations
Wavg
IWC

25. Finite layers MC
IPA

26. Finite simulations
Rmc=0.423
Rppa=0.396

27. Finite simulations
Wavg
IWC

28. Discussion

29. Deep Convection
Gerard Devine (Leeds)

30. Radiative Properties - Reflectance
+2.7 %

31. Radiative Properties - Absorptance
-1.45 %

32. Summary and Conclusions
Developed an Emerald case study
Refined the diffusivity of water vapour
Radiation drives inhomogeneity in cirrus
3D rad:
Inhom stratiform layers: 2-3%
Finite cirrus layers: 6-7%
Competing effects
Deep convection: 2-3% (domain size)

33. Future work Further comparisons with EMERALD and Chilbolton cases
3D radiation effects on EMERALD,
Chilbolton, and Toga-Coare cases
Thanks: NERC CWVC (NER/T/S/2000/00983)

35. Contact: dobbie@env.leeds.ac.uk

36. Future work
[G. Heymsfield]

38. Stability Numbers

42. Layer simulations
(Ripa – Rmc )/Rmc
H ipa for R and H mc for A

43. Finite simulations

44. Instability (No Rad.)

45. Inhomogeneous layer

46. Effect of depth
Keep?

47. Finite cirrus layer

48. 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

49. Effect of shear on vertical correlation of IWC

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

51. Instability (Rad. Influenced)

52. Observed and LEM profiles

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

54. Chilbolton Case Study

55. Radiative Heating Profiles

56. 16 July C-F Anvil Mission P. Lawson D. Baumgardner A. Heymsfield

57. 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.

58. Observed and LEM profiles
Reading, Dec 8

59. Microphysics

60. 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

61. 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

62. Effect of shear on vertical correlation of IWC

63. 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)