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Simultaneous profile measurements of BrO, OClO and NO 2 in the polar vortex

Simultaneous profile measurements of BrO, OClO and NO 2 in the polar vortex. Chris Sioris and Kelly Chance Smithsonian Astrophysical Observatory. Method: Two-step retrieval. Step 1 : Spectral fit. BrO (Wilmouth et al.) OClO (Wahner et al.)

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Simultaneous profile measurements of BrO, OClO and NO 2 in the polar vortex

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  1. Simultaneous profile measurements of BrO, OClO and NO2 in the polar vortex Chris Sioris and Kelly Chance Smithsonian Astrophysical Observatory

  2. Method: Two-step retrieval Step 1: Spectral fit BrO (Wilmouth et al.) OClO (Wahner et al.) NO2 and O3 (Bogumil et al., 203, 223, 243 K) tilt (Sioris et al., uses Chance-Kurucz solar spectrum)

  3. Sample fitted optical depths, BrO fitting window, at TH=10 km in Arctic vortex

  4. Step 2:Vertical “fitting” of SCD profile -pointing correction: 305 nm knee -Forward RTM: McLinden et al., 2002 -inversion: modified Chahine’s method (Sioris et al., 2003) for OClO, retrieval is done on a 1 km altitude grid using measurement TH grid (~3.3 km sampling)

  5. NO2 Validation Typical agreement based on comparisons with OSIRIS, SAGE III, SAOZ, and HALOE is 7% on VCD and 14% profile (15-41 km)

  6. BrO validation BrO VCD (15-27 km) agrees to <5% and profile to 7% with SAOZ-BrO (despite poor temporal coincidence of ~10 hours) At ~23 km, BrO: 26 pptv (10 am LT), 16-20 pptv (before sunset, ascent)

  7. Sample orbit of NO2 Top: SCIAMACHY NO2 number density, cm-3, on August 5, 2002; Bottom: Canadian Middle Atmosphere Model NO2 [de Grandpre et al., 1997].

  8. Sample orbit of BrO- July 24th pptv -Tropical upper tropospheric BrO at 4 ° S, associated with cirrus -Latitudinal distribution as expected [BrO] 18 pptv in the middle stratosphere

  9. • SCIA • OS • • • • • • • • • • Feb. 2003: Arctic

  10. Artic, Feb. 10th, 2003: DeNOxification extends from ~18-28 km

  11. OSIRIS (17-37 km) LT: just after sunrise (SZA 87.5°) molec/cm3 SCIAMACHY (15-41 km) Effect of differences in across-track and vertical resolution 89.7 87 84 77 SZA (am)

  12. Noxon cliff at 50° N

  13. ---------------------------------SCIA VCD=3.53e13 -------SCIA VCD= 1.02e13

  14. Arctic OClO, Feb. 10th, 2002

  15. Arctic BrO VCD (15-27 km, molec/cm2) 61º: 3.4e13 68º: 2.3e13 72º: 5.3e13 75º: 5.7e13 OS VCD 3.4e13

  16. Data from Antarctic winter PSC observation, 65° S in early August (orbit 2293)

  17. PSC at ~20-24 km, August 23rd, 61° S (orbit 2508)

  18. • • • Lat(°S) SCIA VCD (11-41 km) 54 1.63e15 61 7.38e14 68 2.43e14

  19. -DeNOxification extends from 1434 km at 68° S, 1730 km at 61° S -local sunrise, so NO2 is at daytime minimum(variation above is partly diurnal) -at 27 km, 68° S, [NO2] at sunrise is 2107 molec/cm3,  [OClO] , [BrO] -hint of NOx descending from the mesosphere at 68° S

  20. Lat SCIA (°S) VCD (14-28 km) 61 7.6e12 68 1.5e13 * *

  21. • • • Lat SCIA (S) VCD (11-30 km) 54 5.48e13 61 5.83e13 68 3.30e13

  22. Evidence for high BrO mixing ratios in middle stratosphere, at high southern latitudes as well

  23. •Direct confirmation of our understanding of BrO photochemistry in the lower stratosphere at sunrise •[BrO] sharply decreasing with height in the lowermost stratosphere •BrO spike at ~19 km “allowed” by low NO2 at 68° S

  24. Conclusions OClO layer peaks at higher altitude in Antarctic than Arctic at the vortex edge, OClO shows a very limited vertical extent (sharp layer) Denoxification is more severe and covers a greater altitude range in Antarctic than Artic OClO exhibits correlation with BrO and clear anti-correlation with NO2 ; BrO also anti-correlated with NO2 SCIAMACHY stratospheric BrO is in good agreement with GOME total columns outside of polar PBL enhancements BrO mixing ratios of 26 pptv in the middle stratosphere!!!

  25. Final Remark Limb scatter technique can measure scientifically useful profiles of minor trace gases such as BrO and OClO despite their absorption signatures being at the 10-3 level Acknowledgments Florence Goutail and the SAOZ team, Ghassan Taha and the SAGE III team, Michel van Roozendael (IASB), University of Bremen, and Chris McLinden (Environment Canada)

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