1. Atmospheric Science Conference, Frascati, Italy, 8 - 12 May, 2006 Retrieval of BrO vertical distributions from SCIAMACHY limb measurements: Data quality assessment and algorithm improvements A. Rozanov 1, S. Kühl 2, C. Sioris 3, H. Bovensmann 1, J. P. Burrows 1, M. Chipperfield 9, F. Goutail 7, F. Hendrick 4, M. von Hobe 8, S. Hrechanyy 8, C. McLinden 5, K. Pfeilsticker 2, J. Pukite 2, M. van Roozendael 4, R. Salawitch 6, B.-M. Sinnhuber 1, F. Stroh 8, T. Wagner 2 1 Instutute of Environmental Physics, University of Bremen, Germany 2 Instutute of Environmental Physics, University of Heidelberg, Germany 3 Harvard-Smithsonian Center for Astrophysics, Cambridge, USA 4 Belgian Institute for Space Aeronomy (IASB-BIRA), Brussels, Belgium 5 Meteorological Service of Canada, Toronto, Canada 6 Jet Propulsion Laboratory, Pasadena, California, USA 7 Service d’Aeronomie - CNRS, France 8 Juelich Research Center, Germany 9 University of Leeds, UK

2. 2 BOOST: A joint intercomparison project Bromine Oxide in the lOwer STratosphere (BOOST) Project objectives  Comparison of BrO vertical distributions retrieved from SCIAMACHY limb measurements using different retrieval algorithms  Investigation of possible reasons for the disagreement between the retrievals identified in previous studies  Improvement of the existing retrieval algorithms (especially w.r.t. the retrieval quality in the lower stratosphere and the upper troposphere)  Investigation of the sensitivity of the retrieved profiles to the retrieval parameters such as spectral range, initial profiles, cross sections, spectral corrections

3. 3 BOOST: participating groups SCIAMACHY retrieval groups:  IUP, University of Bremen: Alexei Rozanov  IUP, University of Heidelberg: Sven Kühl  Harvard-Smithsonian Center for Astrophysics (SAO): Chris Sioris Balloon-borne and ground-based measurements:  IUP, University of Heidelberg: DOAS, Klaus Pfeilsticker  Juelich Research Center: TRIPLE, Serhiy Hrechanyy  Service d’Aeronomie – CNRS: SAOZ, Florence Goutail  Belgian Institute for Space Aeronomy: ground-based, François Hendrick Modeling groups:  IUP, University of Bremen: Björn-Martin Sinnhuber  Jet Propulsion Laboratory: Ross Salawitch  Meteorological Service of Canada: Chris McLinden  University of Leeds: Martyn Chipperfield

4. 4 Main inversion procedure: Solution: Information Operator or Optimal Estimation Measurement vector: differential signal in all spectral points at all selected tangent heights State vector: trace gas number densities at altitude levels Retrieval algorithm of the University of Bremen Simulated limb spectra Weighting functions w.r.t. concentrations Forward modeling (SCIATRAN) : Fully spherical treatment for SS Approximation for MS Measured and simulated limb spectra Vertically integrated WF Correction parameters Pre-processing (DOAS-like fit) at each tangent height: Shift and squeeze correction Spectral corrections Vertical distributions of trace gas number densities Measured and simulated limb spectra with all corrections applied Weighting functions A priori constraints Next iteration

5. 5 Retrieval algorithm of the University of Heidelberg One iteration only Block Air Mass Factors Forward modeling (TRACY) : Fully spherical Monte Carlo Measured limb spectra Cross sections Slant columns as a function of tangent height DOAS fit for both measured and simulated spectra at each tangent height: Shift Spectral corrections Vertical distributions of trace gas number densities Fitted slant columns Block Air Mass Factors A priori constraints Inversion procedure: Solution: Optimal Estimation (maximum a posteriori) Measurement vector: fitted slant columns State vector: trace gas number densities at altitude levels

6. 6 Inversion procedure (Chahine-like): Retrieval algorithm of SAO Simulated limb spectra Measured or simulated limb spectra Cross sections Slant columns as a function of tangent height DOAS fit for both measured and simulated spectra at each tangent height for a set of temperatures: No shift & squeeze correction Spectral corrections Vertical distributions of trace gas number densities Measured slant columns Simulated slant columns interpolated to an appropriate temperature Forward modeling (VECTOR) : Fully spherical treatment for SS Approximation for MS First iteration: Subsequent iterations: Next iteration

7. 7 Retrieval settings Uni Bremen Uni Heidelberg SAO Spectral range337 – 357 nm 344 – 360 nm Reference tangent height ~ 35 km 33 – 70 km co-addition Spectral corrections shift, 1/I 0, eta, I 0 -correction for O 3, ring shift, ring, 1/I 0, /I 0, I 0 -corrected O 3 cross section, eta, zeta tilt, I 0 -corrected O 3 cross section Temperature dependence fullO 3 cross sections at 223 K and 243 K fitted series of fits with O 3 and NO 2 cross sections at different temperatures Regularization weak statistical, smoothness statistical sharp gradients are not permitted

8. 8 Initial set of the limb states to be compared Selection criteria (based on results from ): Selection criteria (based on results from Dorf at al., 2006):  At the current stage of the project comparisons will be performed for the limb states collocated with:  Three balloon-borne DOAS measurements (photochemically corrected)  Three balloon-borne TRIPLE measurements (uncorrected)  Selected ground-based zenith-sky twilight measurements (presented by Francois Hendrick)  For each balloon flight air mass trajectory calculations were done identifying the forward (being in the future w.r.t. the balloon flight) and the backward (being in the past w.r.t. the balloon flight) match with SCIAMACHY limb observations

9. 9 Selected reference measurements List of DOAS flights:  March 23 rd, 2003; Kiruna (67.9 o N, 21.1 o E); 15:19 - 16:09  October 9 th, 2003; Air sur l’Adour (43.7 o N, 0.3 o W); 15:39 - 17:09  March 24 th, 2004; Kiruna (67.9 o N, 21.1 o E); 13:55 - 17:35 List of TRIPLE flights:  September 24 th, 2002; Air sur l'Adour (43.7 o N, 0.3 o W); balloon ascent: 8:20 - 9:18 UTC  March 6 th, 2003; Kiruna (67.9 o N, 21.1 o E); balloon ascent: 6:30 - 7:56 UTC; balloon descent: 8:33 - 9:44 UTC  June 9 th, 2003; Kiruna (67.9 o N, 21.1 o E); balloon descent: 7:56 - 9:09 UTC Ground-based zenith-sky twilight measurements :  Selected days, Harestua, Norway (60.2 o N, 10.8 o E)

10. 10 Comparisons to balloon-born DOAS (1) Balloon flight: Balloon flight: March 23 rd, 2003; Kiruna (67.9 o N, 21.1 o E); 15:19 - 16:09 Ground based: Ground based: same day sunrise at Harestua, Norway (60.2 o N, 10.8 o E) Backward match: March 23 rd, 2003; 11:07 UT; Orbit 5545; State 7; 75 o N,16 o E Forward match: March 24 th, 2003; 9:01 UT; Orbit 5558; State 10; 56 o N, 26 o E

11. 11 Comparisons to balloon-born DOAS (2) Balloon flight: Balloon flight: October 9 th, 2003; Air sur l’Adour (43.7 o N, 0.3 o W); 15:39 - 17:09 Backward match: October 9 th, 2003; 9:51 UT; Orbit 8407; State 9; 41 o N,8 o E Forward match: October 10 th, 2003; 9:20 UT; Orbit 8421; State 9; 41 o N, 16 o E

12. 12 Comparisons to balloon-born DOAS (3) Comparisons to balloon-born DOAS (3) Balloon flight: Balloon flight: March 24 th, 2004; Kiruna (67.9 o N, 21.1 o E); 13:55 - 17:35 Ground based: Ground based: March 24 th, 2004 sunset at Harestua, Norway (60.2 o N, 10.8 o E) Backward match: March 24 th, 2004; 10:36 UT; Orbit 10798; State 9; 66 o N,9 o E Forward match: March 25 th, 2004; 8:25 UT; Orbit 10811; State 9; 62 o N, 38 o E

13. 13 Comparisons to TRIPLE (1) Balloon flight: Balloon flight: September 24 th, 2002; Air sur l'Adour (43.7 o N, 0.3 o W); balloon ascent: 8:20 - 9:18 UTC; SZA = 65 o - 56 o Backward match: ; Backward match: SZA = 44.5 o ; September 23 rd, 2002; 11:06 UT; Orbit 2954; State 11; 40 o N,10 o W Forward match: Forward match: SZA = 50 o ; September 24 th, 2002; 10:32 UT; Orbit 2968; State 10; 47 o N, 2 o E

14. 14 Comparisons to TRIPLE (2) Balloon flight: Balloon flight: March 6 th, 2003; Kiruna (67.9 o N, 21.1 o E); balloon ascent: 6:30 - 7:56 UTC; SZA = 85 o - 78 o ; balloon descent: 8:33 - 9:44 UTC; SZA = 76 o – 73 o Backward match: Backward match: SZA = 82.6 o ; March 5 th, 2003; 12:13 UT; Orbit 5288; State 6; 76.5 o N,4 o E Forward match: Forward match: SZA = 72.5 o ; March 6 th, 2003; 10:04 UT; Orbit 5301; State 8; 66 o N, 17 o E

15. 15 Comparisons to TRIPLE (3) Balloon flight: Balloon flight: June 9 th, 2003; Kiruna (67.9 o N, 21.1 o E); balloon descent: 7:56 - 9:09 UTC; SZA = 49 o - 45 o Backward match: Backward match: SZA = 81.5 o ; June 8 th, 2003; 19:01 UT; Orbit 6652; State 5; 68 o N,21 o E Forward match: Forward match: SZA = 45.6 o ; June 9 th, 2003; 10:18 UT; Orbit 6661; State 11; 68 o N, 16 o E

16. 16 Dependence on a priori information (1) Balloon flight: October 9 th, 2003 15:39 - 17:09 Air sur l’Adour 43.7 o N, 0.3 o W SCIAMACHY limb: October 10 th, 2003 9:20 UT Orbit 8421, State 9 41 o N, 15 o E University of Bremen retrievals:

17. 17 Dependence on a priori information (2) Balloon flight: October 9 th, 2003 15:39 - 17:09 Air sur l’Adour 43.7 o N, 0.3 o W SCIAMACHY limb: October 10 th, 2003 9:20 UT Orbit 8421, State 9 41 o N, 15 o E SAO retrievals:

18. 18 Conclusions (1) All retrievals agree within error bars  Error bars of SAO retrievals are very large in the lower layers:  60 % at 17 km increasing downwards, often about 100% below 16 km  Below 20 km SAO retrieval tend to produce higher values as compared to Bremen and Heidelberg results  Good agreement between Uni Bremen and SAO retrievals in the upper layers above 22 – 25 km  Retrievals of Uni Heidelberg result in slightly higher values compared to Uni Bremen and SAO retrievals in the upper layers above 20 - 22 km, which is in a better agreement with ground-based measurements but in worse agreement with balloon-born DOAS results  Mostly good agreement between Bremen and Heidelberg in the lower layers below 20 - 22 km.

19. 19 Conclusions (2) Overall good agreement with balloon-born DOAS Variable degree of agreement with TRIPLE  Reasonable agreement with exception of the lowest point for the flight on September 24 th, 2002  Very good agreement for the forward match on June 9 th, 2003, a photochemical correction is required for the backward match  Disagreement for the flight on March 6 th, 2003, further investigations necessary Dependence on a priori information  Uni Bremen retrievals are independent of a priori information down to 17 km and show a weak dependence on the form of a priori profile below. Although retrieval results obtained using different a priori profiles are still in agreement within error bars.  SAO retrievals are found to be nearly independent of the initial profile

20. 20 Outlook Additional comparisons are needed  Additional DOAS flight: June 17 th, 2005  Photochemical correction of the backward match for TRIPLE flight on March 6 th, 2003  Balloon born SAOZ measurements  Ground-based measurements Model simulations and retrievals  SCIATRAN (Uni Bremen)  VECTOR (SAO)  TRACY (Uni Heidelberg) Further investigation of the influence of the spectral range, reference tangent height, and retrieval initialisation parameters