Atmospheric Science Conference, Frascati, Italy, 8 - 12 May, 2006Atmospheric Science Conference, Frascati, Italy, 8 - 12 May, 2006

Retrieval of BrO vertical distributions from Retrieval of BrO vertical distributions from SCIAMACHY limb measurements: SCIAMACHY limb measurements:

Data quality assessment and algorithm improvementsData 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, Germany2 Instutute of Environmental Physics, University of Heidelberg, Germany

3Harvard-Smithsonian Center for Astrophysics, Cambridge, USA

4Belgian Institute for Space Aeronomy (IASB-BIRA), Brussels, 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

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BOOST: A joint intercomparison projectBOOST: A joint intercomparison project

Bromine Oxide in the lOwer STratosphere (BOOST)Bromine Oxide in the lOwer STratosphere (BOOST)

Project objectivesProject 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

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BOOSTBOOST: participating groups: participating groupsSCIAMACHY retrieval 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: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: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

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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 BremenRetrieval 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 appliedWeighting functionsA priori constraints

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Retrieval algorithm of the University of HeidelbergRetrieval algorithm of the University of HeidelbergO

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Block Air Mass FactorsForward 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 columnsBlock Air Mass FactorsA priori constraints

Inversion procedure:• Solution: Optimal Estimation

(maximum a posteriori)• Measurement vector: fitted

slant columns• State vector: trace gas number

densities at altitude levels

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Inversion procedure (Chahine-like):

Retrieval algorithm of SAORetrieval 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 columnsSimulated slant columns interpolated to an appropriate temperature

Forward modeling (VECTOR) :• Fully spherical treatment for SS• Approximation for MS

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Subsequent iterations:

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Retrieval settingsRetrieval settings

Uni BremenUni Bremen Uni HeidelbergUni Heidelberg SAOSAO

Spectral range 337 – 357 nm 337 – 357 nm 344 – 360 nm

Reference tangent height

~ 35 km ~ 35 km 33 – 70 kmco-addition

Spectral corrections

shift, 1/I0, eta,

I0-correction for

O3, ring

shift, ring, 1/I0, /I0, I0-corrected O3 cross section, eta, zeta

tilt, I0-corrected O3 cross section

Temperature dependence

full O3 cross sections at 223 K and 243 K fitted

series of fits with O3 and NO2 cross sections at different temperatures

Regularizationweak statistical, smoothness

statistical sharp gradients are not permitted

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Initial set of the limb states to be comparedInitial 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

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Selected reference measurementsSelected reference measurements

List of DOAS 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: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 :Ground-based zenith-sky twilight measurements :

Selected days, Harestua, Norway (60.2oN, 10.8oE)

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Comparisons to balloon-born DOAS (1)Comparisons to balloon-born DOAS (1)

Balloon flight: Balloon flight: March 23rd, 2003; Kiruna (67.9oN, 21.1oE); 15:19 - 16:09Ground based:Ground based: same day sunrise at Harestua, Norway (60.2oN, 10.8oE)

Backward match:Backward match: March 23rd, 2003; 11:07 UT; Orbit 5545; State 7; 75oN,16oE

Forward match:Forward match: March 24th, 2003; 9:01 UT; Orbit 5558; State 10; 56oN, 26oE

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Comparisons to balloon-born DOAS (2)Comparisons to balloon-born DOAS (2)

Balloon flight: Balloon flight: October 9th, 2003; Air sur l’Adour (43.7oN, 0.3oW); 15:39 - 17:09

Backward match:Backward match: October 9th, 2003; 9:51 UT; Orbit 8407; State 9; 41oN,8oE

Forward match:Forward match: October 10th, 2003; 9:20 UT; Orbit 8421; State 9; 41oN, 16oE

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Comparisons to balloon-born DOAS (3)Comparisons to balloon-born DOAS (3)

Balloon flight: Balloon flight: March 24th, 2004; Kiruna (67.9oN, 21.1oE); 13:55 - 17:35Ground based:Ground based: March 24th, 2004 sunset at Harestua, Norway (60.2oN, 10.8oE)

Backward match:Backward match: March 24th, 2004; 10:36 UT; Orbit 10798; State 9; 66oN,9oE

Forward match:Forward match: March 25th, 2004; 8:25 UT; Orbit 10811; State 9; 62oN, 38oE

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Comparisons to TRIPLE (1)Comparisons to TRIPLE (1)

Balloon flight: Balloon flight: September 24th, 2002; Air sur l'Adour (43.7oN, 0.3oW); balloon ascent: 8:20 - 9:18 UTC; SZA = 65o - 56o

Backward match: Backward match: SZA = 44.5o;; September 23rd, 2002; 11:06 UT; Orbit 2954; State 11; 40oN,10oW

Forward match:Forward match: SZA = 50o; September 24th, 2002; 10:32 UT; Orbit 2968; State 10; 47oN, 2oE

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Comparisons to TRIPLE (2)Comparisons to TRIPLE (2)Balloon flight: 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

Backward match: Backward match: SZA = 82.6o; March 5th, 2003; 12:13 UT; Orbit 5288; State 6; 76.5oN,4oE

Forward match:Forward match: SZA = 72.5o; March 6th, 2003; 10:04 UT; Orbit 5301; State 8; 66oN, 17oE

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Comparisons to TRIPLE (3)Comparisons to TRIPLE (3)Balloon flight: Balloon flight: June 9th, 2003; Kiruna (67.9oN, 21.1oE);

balloon descent: 7:56 - 9:09 UTC; SZA = 49o - 45o

Backward match: Backward match: SZA = 81.5o; June 8th, 2003; 19:01 UT; Orbit 6652; State 5; 68oN,21oE

Forward match:Forward match: SZA = 45.6o; June 9th, 2003; 10:18 UT; Orbit 6661; State 11; 68oN, 16oE

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Dependence on a priori information (1)Dependence on a priori information (1)

Balloon flight: Balloon flight: October 9th, 200315:39 - 17:09Air sur l’Adour 43.7oN, 0.3oW

SCIAMACHY limb:SCIAMACHY limb: October 10th, 20039:20 UTOrbit 8421, State 941oN, 15oE

University of Bremen retrievals:University of Bremen retrievals:

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Dependence on a priori information (2)Dependence on a priori information (2)

Balloon flight: Balloon flight: October 9th, 200315:39 - 17:09Air sur l’Adour 43.7oN, 0.3oW

SCIAMACHY limb:SCIAMACHY limb: October 10th, 20039:20 UTOrbit 8421, State 941oN, 15oE

SAO retrievals:SAO retrievals:

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Conclusions (1)Conclusions (1)

All retrievals agree within error barsAll 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.

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Conclusions (2)Conclusions (2)

Overall good agreement with balloon-born DOASOverall good agreement with balloon-born DOAS

Variable degree of agreement with TRIPLEVariable 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

Dependence on a priori informationDependence 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

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OutlookOutlook

Additional comparisons are neededAdditional 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 retrievalsModel simulations and retrievals SCIATRAN (Uni Bremen) VECTOR (SAO) TRACY (Uni Heidelberg)

Further investigation of the influence of the spectral range, reference Further investigation of the influence of the spectral range, reference tangent height, and retrieval initialisation parameterstangent height, and retrieval initialisation parameters