Cloud sensitivity studies for stratospheric and lower mesospheric

1. Cloud sensitivity studies for stratospheric and lower mesospheric ozone profile retrievals from limb scattered solar radiance T. Sonkaew, C. von Savigny, A. Rozanov, V. Rozanov, H. Bovensmann and J.P. Burrows Institute of Environmental Physics and Remote Sensing, University of Bremen, Bremen, Germany

2. Outline Introduction Methodology Retrieval algorithm and Forward simulation Linear approximation Sensitivity studies Weighting functions Cloud parameters Ground albedo Viewing angles Conclusions Future work 2

3. Introduction Clouds cover 60% of atmosphere, 7% of tropospheric volume. [Lelieveld et al., 1989 and Pruppacher and Jaenicke, 1995] The reflectance at 443 nm from SCIAMACHY data using SACURA, 1 Jan 2006 – 31 Dec 2006 Photo by R. Macatangay 3

4. Introduction Clouds interact with the incoming solar radiation and long wavelength radiation emitted from the Earth. Clouds have an impact on the trace gas retrieval. line of sight 4

5. Cloudiness scenario Radiative transfer code “SCIATRAN” Simulated limb radiance spectra Cloud free scenario Retrieval incloud freescenario Vertical P, T and albedo Ozone vertical profile True ozone profile Ozone profile in cloudy atmosphere How to estimate the impact of clouds on the ozone retrieval? 5

6. Retrieval Algorithm Combined the O3 profile in the Hartley, Hugginsand Chappuis bands 2=602 nm 1= 525 nm 3=675 nm Burrows et al., [1999] The Chappuis bands in visible allow to retrieve O3 between 15-40 km[Flittner,2000; McPeters,2000; vonSavigny,2002] The absorption cross section of O3 in different temperatures and wavelengths in the Chappuis band (red arrows) used for O3 retrievals. 6

7. Retrieval Algorithm The Hartley bands in UV allow to retrieve O3 between 35-65 km. Wavelengths264, 267.5, 273.5, 283, 286, 288, 290 and 305 nm are chosen. [Rohen,2006] 8 Burrows et al., [1999] 7

8. Retrieval Algorithm • Normalization step: reduce impact of ground albedo and cloud on O3 retrieval. • Reference tangent heights: • Combination of the Chappuis bands wavelengths: • Combination of the Hartley and Chappuis bands wavelengths: • employ the retrieval vectors 8

9. Retrieval Algorithm Numerical retrieval step: nonlinear Newtonian iteration optimal estimation [Rodger, 1976] SCIATRAN V 2.2 radiative transfer model [Rozanov et al., 2007] using Discrete Ordinate Method (DOM) [Chandrasekhar, 1950] • SCIATRAN set up • Aerosol : none • Ground albedo : 0.3 (for general cases) • Weighting function : single scattering • Cloud model : Mie phase function 9

10. Use linear approximation to estimate the error. 10

11. Error Estimation + : S = I0at 600 nm ◆ : S = Normalized triple + : S = I0at 600 nm ◆ : S = Normalized triple 11

12. Error Estimation < 0, always + < 0 -> 0 Can we use linear approximation to predict the error? 12

13. Sensitivity studies Weighting functions of cloud-free 13

14. Sensitivity studies Weighting functions of cloud-free andcloudy atmosphere 14

15. Sensitivity studies Different weighting functions of cloud-free andcloudy atmosphere 286 nm 264 nm 273 nm 290 nm CHAPPUIS 305 nm 15

16. The retrieval ozone profiles from synthetic data The combined Hartley, Huggins and Chappuis bands O3 profiles in from modeled calculation in cloud-free and cloudy atmosphere. Cloud parameters: cloud height 4-7 km, τ=20, re=10 m, SZA = 30o, SAA = 30o 16

17. Sensitivity studies • Cloud types : (cloud level and cloud optical thickness)  Low cloud (1-3 km) Middle cloud (2-7 km) High cloud (6-15 km) 0 - 3.6 3.6 – 23 23 – 379 Cumulus Stratocumulus Stratus Altocumulus Altostratus Nimbostratus Cirrus Cirrostratus Deep convection The relative O3 error for low cloud, re = 10 m, and SZA = SAA = 30o (SZA ~ 22o and SAA ~ 70o at TH = 25 km ) The relative O3 error for middle cloud, re=10 m and SZA = SAA = 30o (SZA ~ 22o and SAA ~ 70o at TH = 25 km ) The cloud reflectance at 630 nm as function of . [Roebeling et al., 2005] The relative O3 error for high cloud, re=10 m and SZA = SAA = 30o (SZA ~ 22o and SAA ~ 70o at TH = 25 km ) 17

18. Sensitivity studies Geometrical cloud thickness a) different cloud altitudes The relative error of O3 retrieval profiles for cloud parameters: τ = 10, re = 10 m and SZA = SAA = 30o. 18

19. Sensitivity studies Geometrical cloud thickness b) cloud center 4.9 km c) cloud center 10.5 km The relative error of O3 retrieval profiles for cloud parameters: τ = 10, re = 10 m and SZA = SAA = 30o. 19

20. Sensitivity studies Cloud effective radius 1 0.8 0.6 0.4 0.2 0 0.5 1 1.5 2.0 2.5 The reflection function of water clouds for different values of re at τ= 30 and SZA = 45o. [Kokhanovsky, 2001] The relative error of O3 retrieval profiles for different re. Cloud parameters: τ = 10, 2-7 km and SZA = SAA = 30o 20

21. Sensitivity studies Surface ground albedo The relative error of O3 retrieval profiles for different ground albedo . Cloud parameter: τ = 10, re = 10 m, SZA = SAA= 30o and cloud altitude 2-7 km. 21

22. Sensitivity studies Solar zenith angleSolar azimuth angle The relative error of O3 retrieval profiles for different SZAs . Cloud parameter: τ = 10, re = 10 m, SAA = 30o and cloud altitude 2-7 km. The relative error of O3 retrieval profiles for different SAAs . Cloud parameter: τ = 10, re = 10 m, SZA = 30o and cloud altitude 2-7 km. 22

23. (SZA ≈ 62, SAA ≈ 33 at TH 25 km) (SZA ≈ 30, SAA ≈ 55 at TH 25 km) (SZA ≈ 40, SAA ≈ 130 at TH 25 km) (SZA ≈ 70, SAA ≈ 160 at TH 25 km) (SZA ≈ 78, SAA ≈ 175 at TH 25 km) Sensitivity studies Viewing angles represent for SCIAMACHY Cloud parameter: τ = 10, re = 10 m and cloud altitude 2-7 km. 23

24. Sensitivity studies Overview of cloud sensitivity to O3 Frequent cloud :  < 10, re = 20 m The optical cloud thickness (left) and cloud effective radius (right) from SCIAMACHY data, using SACURA, 19 September 2007. [http://www.iup.physik.uni-bremen.de/~sciaproc/SACURA] 24

25. Sensitivity studies Overview of cloud sensitivity to O3 for frequent cloud * = at TH 25 km 25

26. Comparison results with the error estimation Low bias error ( ε = - ) High bias error ( ε = + ) 26

27. * exact x approximation * exact x approximation 600 nm Triplet ~ 40% ~ 70% 27

28. * exact x approximation Triplet 600 nm * exact x approximation 28

29. Conclusions The combined Chappuis and Hartley band retrieval allows us to obtain the O3 profiles from the lower stratosphere to lower mesosphere. The O3 retrievals are sensitive to clouds in the Chappuis bands, between 15 -25 km sensitive to cloud parameters τ, high cloud and viewing angles not much sensitive to cloud parameters: re. The effect of neglecting clouds in the retrievals is less than 10 % at all altitudes for frequent clouds. Linear approximation can not apply to estimate the O3 retrieval error from clouds. 29

30. Future activities Test, how clouds sensitivity to ozone retrieval depends on SZA and SAA on TH references. 30

31. THE END…. ……..Thank you

32. Retrieval Algorithm In linear approximation, limb radiance corresponding to the perturbed ozone profile can be written: 8

33. High bias error Low bias error High bias error TH Low bias error Low bias error Low bias error Comparison results with the error estimation 26

34. TH Comparison results with the error estimation High bias error Low bias error High bias error Low bias error Low bias error Low bias error 19

35. High bias error Low bias error High bias error Low bias error Low bias error Low bias error 19

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37. Sensitivity studies Solar azimuth angle a) viewing angles represent for SCIAMACHY b) viewing angles represent for OSIRIS Cloud parameter: τ = 10, re = 10 m and cloud altitude 2-7 km. 17

38. Comparison results with the error estimation High bias error Low bias error Low bias error Low bias error Low bias error High bias error 26