Kelly Chance Harvard-Smithsonian Center for Astrophysics kchance@cfa.harvard

1. 2004 ENVISAT Symposium Tropospheric Ozone and Ozone Profiles from GOME Kelly Chance Harvard-Smithsonian Center for Astrophysics kchance@cfa.harvard.edu Xiong Liu, Christopher Sioris, Robert Spurr, Thomas Kurosu, Randall Martin, Michael Newchurch, P.K. Bhartia September 9, 2004

2. Outline • Introduction • Methodology • Validation with Dobson, TOMS, and ozonesondes • Global Distribution of tropospheric ozone • Summary and conclusions

3. Satellite-based Tropospheric Ozone Retrieval • Satellite observations are crucial for studying the global distributions, spatial and temporal variability, sources and sinks, transport, and seasonal behavior of tropospheric ozone. • Challenge: only about 10% of the total ozone, difficult to accurately separate tropospheric ozone and stratospheric ozone • Methods • Residual-based approaches: Total ozone – Stratospheric Ozone • Coarse temporal resolution (i.e., monthly) • Subject to large uncertainties in the assumption made about stratospheric ozone • Limited area coverage (e.g., most of tropospheric ozone retrievals from TOMS are limited in the tropics) • Direct ozone profile retrieval (e.g., from GOME, OMI, SCIAMACHY, TES): forward model simulation + a priori knowledge + spectral fitting

4. MIN Misfit Smoothing and Regularization Methodology • Optimal Estimation • Measurements • GOME Channel 1a and 2b: 289-307 nm, 327-336 nm • Spatial resolution: 960 km x 80 km • Wavelength and radiometric calibrations • Derive variable slit widths and shifts between radiances/irradiances • Fit shifts between trace gas absorption cross-sections and radiances • On-line correction of Ring filling in of the solar and telluric absorption features • Channel 1a: single scaling factor • Channel 2b: 2nd order poly. scaling factor to account for multiple scattering • Perform improved polarization correction using GOMECAL • Perform undersampling correction with a high-resolution solar reference • Perform on-line degradation correction for channel 1a

5. Methodology • Improve forward model simulation • LIDORT + look-up table correction of errors due to neglecting polarization • Cloud-top height and cloud fraction from GOMECAT • Monthly-mean SAGE stratospheric aerosols + GEOS-CHEM tropospheric aerosols • Daily ECMWF temperature profiles and NCAR/NCEP surface pressure • Initial surface albedo derived from 370 nm, which has minimal absorption • Wavelength dependent albedo (2-order polynomial) in channel 2b • A priori • TOMS V8 climatology [McPeters et al., 2003, AGU] • Assume a correlation length of 5 km to construct a priori covariance matrix • Retrieval Grid • Almost the same as 11-layer Umkehr grid except the bottom 2 or 3 layers are modified by the NCAR/NCEP reanalysis tropopause pressure • State Vector: 50 parameters • 11 O3 + 4 albedo (1 for ch1a & 3 for ch2b) + 4 Ring (1 for ch1a & 3 for ch2b) + 8 O3 shift + 8 rad./irrad. shift + 3 degradation correction (ch1a only) + 2 undersampling + 4 NO2 + 2 BrO + 2 SO2 + 2 internal scattering

6. Validation:Hohenpeißenberg (48N, 11E) 1996-2000 • Comparison with TOMS V8 & Dobson total ozone, ozonesonde observation • Dobson/Ozonesonde: within ~8 hours, 1.5° in latitude and ~600 km in longitude • Average TOMS total O3 in GOME pixel

7. Validation: Hohenpeißenberg (48N, 11E), 1996-2000 • Ch1a degradation is well-handled • GOME retrievals agree well with Dobson/TOMS and ozonesonde • GOME-TOMS: 3.2±6.0 DU • GOME-Dobson: 4.6 ± 11.5 DU • GOME-Ozonesonde Strat.: 2.6 ± 13.6 DU • GOME-Ozonesonde Trop.: 0.0 ± 6.2 DU • Average biases are within the range of ozone variability, retrieval and measurement uncertainties.

8. Validation: Java (7.6S, 112.7E), 1996-2000 Enhanced O3 from biomass burning due to 97-98 El Niño

9. Validation: Ascension (8.0S, 14.4W), 1997-1999 Enhanced O3 during biomass burning seasons

10. Validation:Ascension (8.0S, 14.4W), 1997-1999 • Total O3 and tropospheric O3 agree well with TOMS and ozonesonde • GOME-TOMS: 1.4±3.2 DU • GOME-Ozonesonde Trop.: 1.3 ± 8.1 DU • GOME-Ozonesonde Strat.: 14.5 ± 9.1 DU • Large bias in stratospheric O3. Thompson et al. [2002] also reported a ~8% TOMS-SHADOZ difference.

11. Summary of comparisons for both ch1a and ch1a+ch2b retrievals

12. An Orbit of Retrieved Profiles (ch1a)

13. Global Distribution of Tropospheric Ozone High O3 band Low O3 North Africa Biomass Burning Low O3 in the tropical Pacific

14. Tropospheric Ozone (02/01/97-02/28/97)

15. Global Distribution of Tropospheric Ozone High O3 over NA and transport High O3 from biomass burning and transport Low O3 Low O3 in the tropical Pacific

16. Tropospheric Ozone (09/01/97-09/30/97)

17. Summary and Conclusions • Ozone profiles and tropospheric ozone columns are derived from GOME using the optimal estimation approach after detailed treatments of wavelength and radiometric calibration and improvement of forward model inputs. • Retrieved total ozone compares well with TOMS and DOBSON total ozone. • The profiles, stratospheric ozone, and tropospheric ozone compare well with ozonesonde observations except for some stratospheric bias at the tropical stations. • Global distributions of tropospheric ozone are presented. They clearly show signals due to air pollution, biomass burning, and convection.

18. The End This work was supported by the Smithsonian Institution and NASA. We are pleased to acknowledge the cooperation of ESA and the DLR in making these studies possible.

19. Backup Slides

20. Validation: Lauder (45S, 170E), 1996-2000

21. Validation: Lauder (45S, 170E), 1996-2000 • GOME retrievals agree well with Dobson/TOMS and ozonesonde • GOME-TOMS: -3.1±6.8 DU • GOME-Dobson: 0.5± 17.2 DU • GOME-Ozonesonde Strat.: 3.0 ± 9.9 DU • GOME-Ozonesonde Trop.: -0.6 ± 6.0 DU • Average biases are within the range of ozone variability, retrieval and measurement uncertainties.

22. Validation: Hilo (19.5N, 155W), 1996-2000 Dobson O3 is measured at Mauna Loa (elevation: 3.4 km)

23. Validation: Hilo (19.5N, 155W), 1996-2000 • Total O3 and tropospheric O3 agree well with Dobson/TOMS and ozonesonde • GOME-TOMS: -1.3±4.9 DU • GOME-Dobson: 9.3± 5.6 DU • GOME-Ozonesonde Trop.: -0.3 ± 6.6 DU • GOME-Ozonesonde Strat.: 5.9 ± 5.9 DU • Large bias in stratospheric O3 especially after 1998.

24. Validation: Samoa (14.2S, 175.6W), 1996-2000

25. Validation: Samoa (14.2S, 175.6W), 1996-2000 • Total O3 and tropospheric O3 agree well with Dobson/TOMS and ozonesonde • GOME-TOMS: -2.8±3.3 DU • GOME-Dobson: 0.6± 5.6 DU • GOME-Ozonesonde Trop.: 0.8 ± 5.7 DU • GOME-Ozonesonde Strat.: 7.6 ± 10.8 DU • Large bias in stratospheric O3 especially after 1998, similar to another CMDL site Hilo.

26. Validation: Java (7.6S, 112.7E), 1996-2000 • Total O3 and tropospheric O3 agree well with TOMS and ozonesonde • GOME-TOMS: -4.6±3.8 DU • GOME-Ozonesonde Trop.: -0.1 ± 5.8 DU • GOME-Ozonesonde Strat.: 10.8 ± 8.4 DU • Large bias in stratospheric O3. Thompson et al. [2002] also reported an ~8% TOMS-SHADOZ difference.

27. Validation: Nairobi (1.3S, 36.8E), 1998-2000

28. Validation: Nairobi (1.3S, 36.8E), 1998-2000 • Total O3 and tropospheric O3 agree well with Dobson/TOMS and ozonesonde • GOME-TOMS: -1.1±5.1 DU • GOME-Dobson: -1.6± 5.7 DU • GOME-Ozonesonde Trop.: -2.3 ± 7.6 DU • GOME-Ozonesonde Strat.: 8.6 ± 6.5 DU • Large bias in stratospheric O3, slightly larger than the ~2% TOMS-SHADOZ difference.