Kelly ChanceKelly Chance

Harvard-Smithsonian Center for AstrophysicsHarvard-Smithsonian Center for Astrophysics

kchance@cfa.harvard.edu

Xiong LiuXiong Liu, Christopher Sioris, Robert Spurr, , Christopher Sioris, Robert Spurr, Thomas Kurosu, Randall Martin, Michael Thomas Kurosu, Randall Martin, Michael

Newchurch, P.K. BhartiaNewchurch, P.K. Bhartia

September 9, 2004September 9, 2004

2004 ENVISAT Symposium2004 ENVISAT Symposium

Tropospheric Ozone and OzoneTropospheric Ozone and OzoneProfiles from GOMEProfiles from GOME

OutlineOutline

• IntroductionIntroduction

• MethodologyMethodology

• Validation with Dobson, TOMS, and Validation with Dobson, TOMS, and ozonesondesozonesondes

• Global Distribution of tropospheric ozoneGlobal Distribution of tropospheric ozone

• Summary and conclusionsSummary 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 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

22 1

2

2 2

( )a a

Kx YS x x

MIN

Misfit Smoothing and Regularization

20 1 0 2 0' exp( ( / ) ( / ) )F F a a a

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

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

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.

Validation: Hohenpeißenberg (48N, 11E), 1996-2000

Validation: Java (7.6S, 112.7E), 1996-2000

Enhanced O3 from biomass burning due to 97-98 El Niño

Validation: Ascension (8.0S, 14.4W), 1997-1999

Enhanced O3 during biomass burning seasons

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.

Summary of comparisons for both ch1a and ch1a+ch2b retrievals

An Orbit of Retrieved Profiles (ch1a)

Global Distribution of Tropospheric Ozone

Low O3

High O3 band

Low O3 in the tropical Pacific

North Africa Biomass Burning

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

Global Distribution of Tropospheric Ozone

Low O3Low O3 in the tropical Pacific

High O3 over NA and transport

High O3 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 EndThe End

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

Backup Slides

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

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.

Validation: Hilo (19.5N, 155W), 1996-2000 Dobson O3 is measured at Mauna

Loa (elevation: 3.4 km)

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.

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

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.

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.

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

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.