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A. Rozanov 1 , J. P. Burrows 1 , S. Kühl 2 , C. McLinden 3 ,

Retrieval of BrO vertical distributions from SCIAMACHY limb measurements: Data quality assessment and algorithm improvements. A. Rozanov 1 , J. P. Burrows 1 , S. Kühl 2 , C. McLinden 3 , K. Pfeilsticker 2 , J. Pukite 2 , R. Salawitch 4 , B.-M. Sinnhuber 1 , C. Sioris 5 , T. Wagner 2.

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A. Rozanov 1 , J. P. Burrows 1 , S. Kühl 2 , C. McLinden 3 ,

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  1. Retrieval of BrO vertical distributions from SCIAMACHY limb measurements: Data quality assessment and algorithmimprovements A. Rozanov1, J. P. Burrows1,S. Kühl2,C. McLinden3, K.Pfeilsticker2, J. Pukite2, R. Salawitch4, B.-M. Sinnhuber1, C. Sioris5, T. Wagner2 1Instutute of Environmental Physics, University of Bremen, Germany 2 Instutute of Environmental Physics, University of Heidelberg, Germany 3Meteorological Service of Canada, Toronto, Cananda 4Jet Propulsion Laboratory, Pasadena, California, USA 5Harvard-Smithsonian Center for Astrophysics, Cambridge, USA

  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 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 initial profiles, cross sections, spectral corrections Participating retrieval groups • IUP, University of Bremen: Alexei Rozanov • IUP, University of Heidelberg: Sven Kühl • Harvard-Smithsonian Center for Astrophysics (SAO): Chris Sioris

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

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

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

  6. Retrieval settings

  7. Initial set of the limb states to be compared • Selection criteria (based on results from Dorf at al., 2006): • At the first stage of the project comparisons will be performed for the limb states collocated with selected balloon-borne DOAS measurements • For each balloon flightair 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 • List of selected balloon flights: • March 23rd,2003; Kiruna (67.9oN, 21.1oE); 15:19 - 16:09 • October 9th, 2003; Air sur l’Adour (43.7oN, 0.3oW); 15:39 - 17:09 • March 24th,2004; Kiruna (67.9oN, 21.1oE); 13:55 - 17:35

  8. Stratospheric temperature at matching states

  9. Temperature dependence of BrO cross sections Convolved Fleischmann cross sections (FWHW = 0.2 nm)

  10. Cross sections comparison: Fleischmann vs. Wilmouth Absolute difference after scaling, shift and squeeze Convolved cross sections (FWHM = 0.2 nm) Scaling factors (Wimouth/Fleischmann): 1.03 @ 298 K, 1.11 @ 228/223 K Relative shift: 0.004 – 0.006 nm @298 K 0.009 nm – 0.02 nm @ 228/223 K

  11. Cross sections comparison: Wahner Convolved cross sections (Wahner fitted to Wilmouth) Convolved cross sections (FWHM = 0.4 nm) Scaling factors (Wahner): 1.0 w.r.t Wilmouth, 0.9 w.r.t. Fleischmann Shift (Wahner): 0.25 – 0.29 nm Wilmouth, 0.23 – 0.27 nm w.r.t. Fleischmann

  12. Comparison between different retrievals (1) Balloon flight: March 23rd,2003; Kiruna (67.9oN, 21.1oE); 15:19 - 16:09 Backward match: March 23rd,2003; 11:07 UT; Orbit 5545; State 7; 41oN,16oE Forward match: March 24th,2003; 9:01 UT; Orbit 5558; State 7; 56oN, 26oE

  13. Comparison between different retrievals (2) Balloon flight: October 9th, 2003; Air sur l’Adour (43.7oN, 0.3oW); 15:39 - 17:09 Backward match: October 9th,2003; 9:51 UT; Orbit 8407; State 9; 41oN,8oE Forward match: October 10th,2003; 9:20 UT; Orbit 8421; State 9; 41oN, 16oE

  14. Comparison between different retrievals (3) Balloon flight: March 24th,2004; Kiruna (67.9oN, 21.1oE); 13:55 - 17:35 Backward match: March 24th,2004; 10:36 UT; Orbit 10798; State 9; 66oN,9oE Forward match: March 25th,2004; 8:25 UT; Orbit 10811; State 9; 62oN, 38oE

  15. Dependence on a priori information University of Bremen retrievals: Balloon flight: October 9th, 2003 15:39 - 17:09 Air sur l’Adour 43.7oN, 0.3oW SCIAMACHY limb: October 10th, 2003 9:20 UT Orbit 8421, State 9 41oN, 15oE

  16. Dependence on a priori information University of Heidelberg SAO

  17. Conclusions 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 > 100% below 16 km • Retrievals of Uni Heidelberg result in slightly higher values compared to Uni Bremen retrievals over the whole altitude range • Below 20 km SAO retrieval tend to produce higher values as compared to Bremen and Heidelberg results • Dependence on a priori information • Below 20 km Uni Heidelberg retrievals show a dependence on a priori profiles • Below 17 km Uni Bremen retrievals show a dependence on the form of a priori profiles but not on the absolute values • SAO retrievals are found to be independent of the initial profile Effect of cross sections is estimated to be about 10%

  18. Outlook Additional comparisons are needed • Additional DOAS flight: June 17th, 2005 • Balloon-borne in-situ measurements with TRIPLE • Balloon born SAOZ measurements • Model simulations and retrievals • SCIATRAN (Uni Bremen) • VECTOR (SAO) • TRACY (Uni Heidelberg) Further investigation of the influence of the initialisation parameters

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