1. Xiong Liu, Kelly Chance, and Thomas Kurosu Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA The 36 th COSPAR Scientific Assembly Beijing, China, July 19, 2006 An Eight-Year Record of Ozone Profiles and Tropospheric Column Ozone from GOME

2. 2 Outline Introduction Examples of Retrievals Algorithm Description Retrieval Characterization Intercomparison with TOMS, Dobson/Brewer, SAGE, and Ozonesonde Measurements Summary and Future Outlook

3. 3 Introduction Tropospheric O 3 : key species in air quality, climate, trop. chemistry Chance et al. (1997): ozone profiles including tropospheric ozone can be derived from UV/Visible spectra (wavelength-dependent photon penetration and temperature-dependent Huggins bands) GOME: April 1995, 240-790 nm, 0.2-0.4 nm FWHM, high SNR Several other groups developed physically-based ozone profile algorithms: Munro et al., 1998; Hoogen et al., 1999, Hasekamp and Landgraf, 2001, van der A et al., 2002 Tropospheric ozone retrievals remain challenging: consistent and accurate calibration, high fitting precision, 90% total ozone above We recently developed our own ozone profile algorithm for GOME data and demonstrated that valuable tropospheric ozone can be derived from GOME (Liu et al., 2005, 2006a, 2006b, in press, 2006c submitted to ACP).

4. 4 Ozone holeBiomass burning over Indonesia Examples of Retrievals (Ozone Profile)

5. 5 Examples of Tropospheric Column Ozone (TCO) Biomass burning over IndonesiaZonal contrast in the tropics

6. 6 An Eight-Year Record of GOME TCO (07/1995-06/2003)

7. 7 Algorithm Description Fitting Windows: 289-307 nm, 325-340 nm, 368-372 nm (cloud) Spatial resolution: 960  80 km 2 Spectral fitting + Optimal estimation + LIDORT A Priori: ozone profile climatology by McPeters et al. [2003] Measurement error: GOME random-noise error Detailed treatments of wavelength and radiometric calibrations Standard correction provided in GDP extraction software Variable slit/wavelength calibration Undersampling correction Include a 2 nd -order polynomial in the fitting in 289-307 nm Derive degradation in reflectance: necessary for the 8-year record

8. 8 Algorithm Description Derive reflectance degradation: comparing averaged reflectance over 60ºN-60ºS to those in the first 6 months and removing SZA and seasonal dependent components Large degradation (up to 25%) and strong wavelength dependence

9. 9 Algorithm Description LIDORT (pseudo-spherical) with additional corrections Polarization correction Ring effect: directly model the 1 st -oder RRS of the direct beam Clouds: Lambertian + IPA, GOMECAT CTP, f c from 368-372 nm Aerosols: SAGE stratospheric and GOCART tropospheric Surface albedo: varying with, initialized from an albedo database NCEP surface & tropopause pressure, ECMWF temperature Directly model and fit other trace gases: SO 2, NO 2, BrO, HCHO NO 2 : PRATMO (stratosphere) + GEOS-CHEM (troposphere) BrO: PRATMO (stratosphere) + well mixed in the troposphere SO 2 /HCHO: no stratospheric + GEOS-CHEM (troposphere) Use ozone cross section by Brion et al. [1993]: reduce residuals by 30-45% in the Huggins bands (vs. Bass-Paur and GOME FM) Fitting residuals: < 0.1% in the Huggins bands (326-340 nm)

10. 10 Retrieval Characterization --- Averaging Kernels VR: 7-12 km (at 10-37 km) 8-12 km (at 20-38 km) DFS: ranging from 1.2 in the tropics to 0.5 at high latitudes

11. 11 Error Analysis Smoothing + Precision: 5-10% in the stratosphere & 20-30% in the troposphere Smoothing + Precision: TO: 3 DU (1.0%) SCO: 2-5 DU (1-2%) TCO: 3-6 DU (12-20%)

12. 12 Total Column Ozone Comparison Comparisons with total ozone /ozonesonde at 33 sonde stations TOMS: mean biases are <6 DU (2%) at most stations with 1  <1.5% in tropics and <2.4% at high latitudes Dobson: ±8hrs, ±1.5ºlat, ±500km lon, mean biases are mostly <5 DU (2%) with 1  < 3% in the tropics and <5% at high latitudes

13. 13 Comparison with Ozonesonde TCO

14. 14 Comparison with Ozonesonde TCO GOME TCO captures most of the temporal variability in ozonesonde TCO Mean biases: <3.3 DU (15%) at 30 stations 1  : 3-8 DU (12-27%)

15. 15 Intercomparison with SAGE-II Comparisons with SAGE-II in 1996-1999 down to ~15 km: same day, ±1.5ºlat, ±5ºlon Systematic biases: usually <15% with 1  <10% at ~20-60 km Column ozone: <2.5 DU at ~15-35 km

16. 16 Comparison with Ozonesonde and SAGE-II SCO Stratospheric column ozone between layer 4 and 7 (15~35 km) or between tropopause and layer 7 GOME/SONDE SCO (15-35 km): usually higher by 8-20 DU (5-8%) at CI & most tropical stations GOME/SAGE-II SCO (~15-35 km): usually within ±2.5 DU (1.5%) except for 3 Northern European stations

17. 17 Profile Comparison with Ozonesonde and SAGE-II GOME/SAGE-II: usually <5% at layer 5 and 8-20% for layer 4 GOME/Sonde: mostly 5-20% for layer 5 and 20-60% for layer 4 GOME/sonde biases depends on sonde technique, sensor solution, and data processing, demonstrating the need to homogenize ozonesonde observations for reliable satellite validation

18. 18 Summary and Future Outlook Ozone profiles and tropospheric column ozone are retrieved from GOME spectra (289-307 nm, 325-340 nm) using the optimal estimation after extensive treatments of wavelength and radiometric calibrations and forward modeling Retrieval have been extensively evaluated against TOMS, Dobson/Brewer, SAGE, and ozonesonde measurements. An eight-year (July 1995-June 2003) record of ozone profiles (24-layers), total, stratospheric, and tropospheric column ozone from GOME is available. Continue to improve the retrievals and apply this algorithm to SCIAMACHY, GOME-2, and OMI data. Integrate with chemical transport model to understand global distribution of tropospheric ozone and its seasonal and interannual variability. Tropospehric ozone budget and its radiative forcing

19. 19 Acknowledgements Supported by NASA and the Smithsonian Institution ESA and DLR TOMS, SAGE, WOUDC, SHADOZ, CMDL NCEP, ECMWF, GEOS-CHEM, GOCART, PRATMO Cluster machine and its support at Harvard- Smithsonian CFA

20. 20 High Resolution Solar Reference Spectrum

21. 21 Variable Slit/Wavelength Calibration n Use GDP extraction software with all standard corrections n Instrument slit function characterization (Chance, 1998) u Assume Gaussian, use non-linear least squares fitting u High resolution solar reference spectrum (Caspar and Chance, 1998) u Variable slit widths (21 spectral pixels in 5-pixel increments)

22. 22 Correction with Climatology/Observations

23. 23 Fitting Residuals

24. 24 Effects of Ozone Cross Sections on Retrievals

25. 25 Effects of Ozone Cross Sections on Retrievals

26. 26 A Priori Influence (06/7-9/1997) TOMS V8 A Priori GEOS-CHEM A Priori Retrieval with TOMS V8 A Priori Retrieval with GEOS-CHEM A Priori

27. 27 Informational Analysis --- DFS and A Priori Influence DFS: 1.2 DFS in the tropics, 0.5 at high latitudes A Priori influence in TCO: 15% in the tropics, 50% at high-latitudes

28. 28 Error Analysis Liu et al., 2005, JGR

29. 29 Comparison with Ozonesonde TCO

30. 30 n Mean biases: <3.3 DU (15%) at 30 stations; 1  : 3-8 DU (12-27%) n Improvements over a priori at most stations: either reduces MBs or 1  or increases the correlation Comparison with Ozonesonde Tropospheric Column Ozone

31. 31 Comparison with Ozonesonde SCO http://www.cmdl.noaa.gov/infodata/ftpdata.html n GOME SCO compares better with 1%-KI buffered than 2%-KI unbuffered by 11-16 DU. n Altitude-dependent total ozone normalization reduces the bias contrast and GOME/sonde biases mainly with 2%-KI unbuffered.

32. 32 Profile Comparison with Ozonesonde n Systematic biases n Large positive biases of (30-70%) at Carbon Iodine and most tropical stations

33. 33 Profile Comparison with Ozonesonde n The biases relative to 1%-buffered is usually smaller by 5-15%. n Altitude-dependent homogenization reduces the bias with 2%-unbuffered. n Uncorrected altitude hysteresis can account for 5-15% biases.

34. 34 GOME vs. GEOS-CHEM Similar overall structures nGlobal biases: <2±4 DU, r=0.82-0.9 n SH: <1±2 DU,r=0.94-0.98 n NH: <4.3±4.6 DU, r=0.6-0.8

35. 35 GOME vs. GEOS-CHEM nUsually within 5 DU. nLarge positive bias of 5-15 DU at some northern tropical and subtropical regions: central America, tropical North Africa, Southeast Asia, Middle East

36. 36 GOME vs. GEOS- CHEM & MOZAIC