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A. Rozanov 1 , S. Kühl 2 , C. Sioris 3 , H . Bovensmann 1 , J. P. Burrows 1 ,

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## A. Rozanov 1 , S. Kühl 2 , C. Sioris 3 , H . Bovensmann 1 , J. P. Burrows 1 ,

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**Retrieval of BrO vertical distributions from SCIAMACHY limb**measurements: Data quality assessment and algorithm improvements A. Rozanov1, S. Kühl2,C. Sioris3, H. Bovensmann1, J. P. Burrows1, M. Chipperfield9, F. Goutail7, F. Hendrick4, M. von Hobe8, S. Hrechanyy8, C. McLinden5,K.Pfeilsticker2, J. Pukite2, M.van Roozendael4, R. Salawitch6, B.-M. Sinnhuber1, F. Stroh8, T. Wagner2 • 1Instutute of Environmental Physics, University of Bremen, Germany • 2 Instutute of Environmental Physics, University of Heidelberg, Germany • 3Harvard-Smithsonian Center for Astrophysics, Cambridge, USA • 4Belgian Institute for Space Aeronomy, IASB-BIRA, Belgium • 5Meteorological Service of Canada, Toronto, Canada • 6Jet Propulsion Laboratory, Pasadena, California, USA • 7Service d’Aeronomie - CNRS, France • 8Juelich Research Center, Germany • 9University of Leeds, UK**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**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**Next iteration**Retrieval algorithm of the University of Bremen • Forward modeling (SCIATRAN) : • Fully spherical treatment for SS • Approximation for MS Simulated limb spectra Weighting functions w.r.t. concentrations 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 Measured and simulated limb spectra with all corrections applied Weighting functions A priori constraints • 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 Vertical distributions of trace gas number densities**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 • Forward modeling (TRACY) : • Fully spherical Monte Carlo Block Air Mass Factors • DOAS fit for both measured and simulated spectra at each tangent height: • Shift • Spectral corrections One iteration only • Inversion procedure: • Solution: Optimal Estimation (maximum a posteriori) • Measurement vector: fitted slant columns • State vector: trace gas number densities at altitude levels Fitted slant columns Block Air Mass Factors A priori constraints**Next iteration**Retrieval algorithm of SAO • Forward modeling (VECTOR) : • Fully spherical treatment for SS • Approximation for MS 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**Initial set of the limb states to be compared**• 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 (photochemically corrected) • 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**Selected balloon flights**• List of DOAS 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 • List of TRIPLE flights: • September 24th, 2002; Air sur l'Adour (43.7oN, 0.3oW); balloon ascent: 8:20 - 9:18 UTC • March 6th, 2003; Kiruna (67.9oN, 21.1oE); balloon ascent: 6:30 - 7:56 UTC; balloon descent: 8:33 - 9:44 UTC • June 9th, 2003; Kiruna (67.9oN, 21.1oE); balloon descent: 7:56 - 9:09 UTC • Ground-based zenith-sky twilight measurements : • Selected days, Harestua, Sweden (60.2oN, 10.8oE)**Comparisons to balloon-born DOAS (1)**Balloon flight: March 23rd,2003; Kiruna (67.9oN, 21.1oE); 15:19 - 16:09 Ground based: same day sunrise at Harestua, Sweden (60.2oN, 10.8oE) Backward match: March 23rd,2003; 11:07 UT; Orbit 5545; State 7; 75oN,16oE Forward match: March 24th,2003; 9:01 UT; Orbit 5558; State 10; 56oN, 26oE**Comparisons to balloon-born DOAS (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**Comparisons to balloon-born DOAS (3)**Balloon flight: March 24th,2004; Kiruna (67.9oN, 21.1oE); 13:55 - 17:35 Ground based:March 24th,2004 sunset at Harestua, Sweden (60.2oN, 10.8oE) 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**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**Effect of BrO cross section: Fleischmann vs. Wilmouth**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**Comparisons to TRIPLE (1)**Balloon flight: September 24th, 2002; Air sur l'Adour (43.7oN, 0.3oW); balloon ascent: 8:20 - 9:18 UTC; SZA = 65o - 56o Forward match:SZA =50o; September 24th, 2002; 10:32 UT; Orbit 2968; State 10; 47oN, 2oE Backward match: SZA =44.5o;September 23rd, 2002; 11:06 UT; Orbit 2954; State 11; 40oN,10oW**Comparisons to TRIPLE (2)**Balloon flight: March 6th, 2003; Kiruna (67.9oN, 21.1oE); balloon ascent: 6:30 - 7:56 UTC; SZA = 85o - 78o; balloon descent: 8:33 - 9:44 UTC; SZA = 76o – 73o Forward match:SZA = 72.5o; March 6th, 2003; 10:04 UT; Orbit 5301; State 8; 66oN, 17oE Backward match: SZA = 82.6o; March 5th, 2003; 12:13 UT; Orbit 5288; State 6; 76.5oN,4oE**Comparisons to TRIPLE (3)**Balloon flight: June 9th, 2003; Kiruna (67.9oN, 21.1oE); balloon descent: 7:56 - 9:09 UTC; SZA = 49o - 45o Forward match:SZA = 45.6o; June 9th, 2003; 10:18 UT; Orbit 6661; State 11; 68oN, 16oE Backward match: SZA = 81.5o; June 8th, 2003; 19:01 UT; Orbit 6652; State 5;68oN,21oE**Comparison to ground-based measurements**Zenith-sky twilight measurements at Harestua, Sweden (60.2oN, 10.8oE)**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**Dependence on a priori information**University of Heidelberg SAO**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.**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 24th, 2002 • Very good agreement for the forward match on June 9th, 2003, a photochemical correction is required for the backward match • Disagreement for the flight on March 6th, 2003, further investigations necessary More comparisons needed to draw any conclusion for ground-based measurements**Conclusions (3)**• Dependence on a priori information • Uni Heidelberg retrievals are independent of a priori profiles down to 20 km and show a clear dependence below. Although retrieval results obtained using different a priori profiles are still agree within error bars. • Uni Bremen retrievals are independent of a priori information down to 17 km and show a weak dependence of the form of a priori profile below. Similar to Heidelberg retrievals the deviations between results obtained using different a priori profiles are always below the error bars. • SAO retrievals are found to be independent of the initial profile**Outlook**Additional comparisons are needed • Additional DOAS flight: June 17th, 2005 • Photochemical correction of the backward match for TRIPLE flight on March 6th, 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 region, reference tangent height, and retrieval initialisation parameters