Stratospheric and Mesospheric Applications of SCIAMACHY Limb Observations

1. Stratospheric and Mesospheric Applications of SCIAMACHY Limb Observations 5th German SCIAMACHY Validation Team Meeting C. von Savigny, A. Rozanov, G. Rohen, K.-U. Eichmann, E. J. Llewellyn*, J. W. Kaiser+, M. Sinnhuber, M. Scharringhausen, P. Ulasi, H. Bovensmann, and J. P. Burrows Institute of Environmental Physics/Remote Sensing, University of Bremen, Bremen, Germany * Department of Physics and Physics Engineering, University of Saskatchewan, Saskatoon, Canada + Remote Sensing Laboratories, University of Zurich, Zurich, Switzerland

2. Stratospheric applications Polar stratospheric clouds Minor constituent profiles Mesospheric applications Mesospheric ozone profiles OH* (3-1) rotational temperature retrievals Noctilucent clouds Outline

3. Illustration of the limb-scattering geometry SCIAMACHY Limb Geometry • Tangent height range: 0 to 100 km • Tangent height step size: 3.3 km • Vertical FOV: 2.6 km • Observation optimised for limb-nadir matching • Duration of Limb sequence: 60 s • Observed is limb scattered solar radiation and terrestrial airglow emissions • On the Earth’s night side limb emissions are observed in a dedicated mesosphere / thermosphere observation mode with tangent height between 75 and 150 km.

4. Polar Stratospheric Clouds

5. PSC detection with limb measurements Step I: Determine colour index profiles Step II: Determine vertical gradient of CI(TH): with  TH = 3.3 km Theoretical maximum (TH) values for 15-30 km altitude range: a) 1.05 for pure Rayleigh atmosphere b) 1.1 for stratospheric background aerosol c) 1.16 for moderate volcanic aerosol d) 1.55 for extreme volcanic aerosol Detection threshold chosen:(TH) = 1.3 detection is somewhat biased towards optically thicker PSCs

6. PSC maps Maps of detected PSCs (open circles: detected PSCs) superimposed to UKMO temperature field at 550 K potential temperature (about 22 km) for August 7-12, 2003.

7. Temporal variation of PSC altitudes 190 190 195 190 190 195 195 195 No SCIAMACHY Observations No SCIAMACHY Observations No SCIAMACHY Observations PSC descent rates for 2003: Santacesaria et al. [2001] : 2.5 km / month at 66º S / 140º E based on a 9-year Lidar climatology Fromm et al. [1997] : 2.0 km / month derived from POAM II

8. Histograms of temperature at PSC altitude

9. Stratospheric Minor Constituents

10. The scia-arc website • The scia-arc website provides value-added scientific data products • Presently available limb data products: stratospheric profiles of O3, NO2 and BrO • In preparation: - mesospheric O3 profiles - maps of NLCs and PSCs - OH rotational temperatures at the mesopause http://www.iup.physik.uni-bremen.de/scia-arc

11. One week before the major stratospheric warming: September 12, 2002 Savigny et al. [2004]

12. The ozone hole split: September 27, 2002

13. At mid-latitudes typical BrO mixing ratios are about 10 pptv, corresponding to about 50 % of the available inorganic bromine (20 pptv). The rest is almost exclusively BrONO2 .[e.g., Sinnhuber et al., 2002] • Within the vortex BrO mixing ratios are most likely enhanced due to the reduced NO2, therefore reduced formation of BrONO2.

14. OH rotational temperature retrievals

15. Retrieval of OH* (3-1) rotational temperatures • OH* produced and vibrationally-rotationally excited at mesopause altitudes by: • H + O3 OH* (v’  9) + O2 + 3.3 eV • Airglow emission centered around 87 km with about 8 km FWHM • Relative population of rotational levels governed by Boltzmann’s distribution • Measurements of relative intensities of rotational emission lines makes • retrieval of OH rotational temperature possible • OH*(v’ = 3) is in local thermodynamical equilibrium (LTE) for lower rotational quantum numbers because: • - collisional frequency at 86 km is 3  104 s-1 • - lifetime of OH at v’ = 3 is about 0.014 s • rotational temperatures are equal to kinetic temperature of ambient air

16. R-branch Q-branch P-branch  J = + 1  J = -1  J = 0 J’=5 Selection rule: J = 0,+1,-1 J’=4 ’=3 J’=3 J’=2 J’=1 J’=0 J’’=5 EJ J(J+1) J’’=4 ’’=1 Q-branch P-branch J’’=3 J’’=2 J’’=1 J’’=0

17. Sample OH spectral fit • Iterative retrieval approach: • linear fit with 2nd order polynomial • (2) non-linear fit (Levenberg-Marquard) • driving OH model, including -shift Impact of different Einstein coefficients used: Kovacs [1969], Mies [1974], Goldman et al. [1998] TKovacs – TMies = 1.1 K and TKovacs – TGoldman = 3.2 K

18. Coverage of Limb eclipse measurements Calibration measurements Limb measurements Calibration measurements Limb measurements Calibration measurements

19. SCIAMACHY Operations Change Request 19 • Replacement of nighttime Nadir observations by limb observations • Implemented on September 6, 2004

20. First validation results GRound-based Infrared P-branch Spectrometer (GRIPS) I at Hohenpeissenberg (47° N / 11° E) GRIPS-I data provided by Michael Bittner and Kathrin Höppner (DLR) Mesospheric Temperature Mapper (MTM) at Hawaii (21° N / 204° E) MTM data provided by Mike Taylor and Yucheng Zhao (Utah State University)

21. OH-Temperatures 2003 • Temperatures: • for latitudes from –20 to 70 deg • from July 2002 up to now.

22. Mesospheric Ozone

23. Averaging kernels Weighting functions

24. Ozone depletion during the Oct. / Nov. 2003 SPEs HOx production by ionization: O2+ + O2 + M  O2+•O2 + M O2+•O2 + H2O O2+•H2O + O2 O2+•H2O + H2O H3O+•OH + O2 H3O+•OH + H2O  H3O+• H2O + OH H3O+• H2O + e- 2 H2O + H O2+ + H2O + e- O2 + H + OH (Courtesy M.-B. Kallenrode and M. Sinnhuber ) NOx is formed as well

25. Ozone depletion during the Oct. / Nov. 2003 SPEs • Ozone loss at 55 km and north of magnetic 60° N relative to October 20 – 24 reference period • 40 MeV protons penetrate the atmosphere Down to about 45 km altitude

26. Observations vs. Model Percent ozone loss north of 60° N magnetic latitude SCIAMACHY measurements Reference period: October 20 – 24, 2003 Model simulations (M. Sinnhuber)

27. Noctilucent Clouds

28. Detection of Noctilucent Clouds (NLCs) UV limb radiance profiles with NLCs and without NLCs

29. NLC particle size determination I I.In single scattering approximation the PMC backscatter is given by: q(,): Differential scattering cross section S(): Solar irradiance spectrum II.The sun-normalized PMC backscatter spectrum: with spectral exponent 

30. NLC particle size determination II The spectral exponent  is related to the PMC particle sizes by Mie-calculations • Assumptions: • Mie theory, i.e., homogeneous dielectric • spheres • Refractive index of ice [Warren, 1984] • Log-normal distribution Simulated spectral exponents for log-normal distribution with  = 1.4 Ambiguity:spectral exponent does not monotonically increase with increasing radius Use several and significantly different wavelengths to determine r and  [von Cossart et al, 1999].

31. NLC particle size determination – January 2003

32. Conclusions • SCIAMACHY limb observations with their broad spectral coverage and extended altitude range both on the day and nightside allows a wide range of stratospheric and mesospheric to be studied: • Optically thin aerosols like NLCs and PSCs • Minor constituent profiles (O3, NO2, BrO; soon H2O, CH4) • Mesopause temperature (soon Rayeigh temperatures)