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

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

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

Methodology n Optimal Estimation n Measurements  GOME Channel 1a and 2b: nm, nm  Spatial resolution: 960 km x 80 km n 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: 2 nd 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 MIN MisfitSmoothing and Regularization

Methodology n 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 n A priori  TOMS V8 climatology [McPeters et al., 2003, AGU]  Assume a correlation length of 5 km to construct a priori covariance matrix n 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 n State Vector: 50 parameters  11 O albedo (1 for ch1a & 3 for ch2b) + 4 Ring (1 for ch1a & 3 for ch2b) + 8 O 3 shift + 8 rad./irrad. shift + 3 degradation correction (ch1a only) + 2 undersampling + 4 NO BrO + 2 SO internal scattering

n 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 O 3 in GOME pixel Validation: Hohenpeißenberg (48N, 11E)

n Ch1a degradation is well-handled n 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 n Average biases are within the range of ozone variability, retrieval and measurement uncertainties. Validation: Hohenpeißenberg (48N, 11E),

Validation: Java (7.6S, 112.7E), Enhanced O 3 from biomass burning due to El Niño

Validation: Ascension (8.0S, 14.4W), Enhanced O 3 during biomass burning seasons

Validation: Ascension (8.0S, 14.4W), n Total O 3 and tropospheric O 3 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 n Large bias in stratospheric O 3. Thompson et al. [2002] also reported a ~8% TOMS-SHADOZ difference.

Summary of comparisons for both ch1a and ch1a+ch2b retrievals

An Orbit of Retrieved Profiles (ch1a)

Global Distribution of Tropospheric Ozone Low O 3 High O 3 band Low O 3 in the tropical Pacific North Africa Biomass Burning

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

Global Distribution of Tropospheric Ozone Low O 3 Low O 3 in the tropical Pacific High O 3 over NA and transport High O 3 from biomass burning and transport

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

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.

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.

Backup Slides

Validation: Lauder (45S, 170E),

n 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 n Average biases are within the range of ozone variability, retrieval and measurement uncertainties.

Validation: Hilo (19.5N, 155W), Dobson O 3 is measured at Mauna Loa (elevation: 3.4 km)

Validation: Hilo (19.5N, 155W), n Total O 3 and tropospheric O 3 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 n Large bias in stratospheric O 3 especially after 1998.

Validation: Samoa (14.2S, 175.6W),

n Total O 3 and tropospheric O 3 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 n Large bias in stratospheric O 3 especially after 1998, similar to another CMDL site Hilo.

Validation: Java (7.6S, 112.7E), n Total O 3 and tropospheric O 3 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 n Large bias in stratospheric O 3. Thompson et al. [2002] also reported an ~8% TOMS-SHADOZ difference.

Validation: Nairobi (1.3S, 36.8E),

n Total O 3 and tropospheric O 3 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 n Large bias in stratospheric O 3, slightly larger than the ~2% TOMS- SHADOZ difference.