Xiong Liu, Kelly Chance, and Thomas Kurosu

Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA

The 36th COSPAR Scientific Assembly

Beijing, China, July 19, 2006

An Eight-Year Record of Ozone Profiles and Tropospheric Column Ozone from GOME

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Outline

Introduction

Examples of Retrievals

Algorithm Description

Retrieval Characterization

Intercomparison with TOMS, Dobson/Brewer, SAGE, and Ozonesonde Measurements

Summary and Future Outlook

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IntroductionTropospheric O3: 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).

4Ozone hole Biomass burning over Indonesia

Examples of Retrievals (Ozone Profile)

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Examples of Tropospheric Column Ozone (TCO)

Biomass burning over IndonesiaZonal contrast in the tropics

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

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Algorithm Description Fitting Windows: 289-307 nm, 325-340 nm, 368-372 nm (cloud) Spatial resolution: 960 80 km2

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 2nd-order polynomial in the fitting in 289-307 nm Derive degradation in reflectance: necessary for the 8-year record

2 2

2

2 2

{ ( - ) -[ F( )]} ( - ) a

1 1- -2 2

y i i+1 i i i+1 aS K X X Y - X S X X

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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

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Algorithm Description LIDORT (pseudo-spherical) with additional corrections

Polarization correction Ring effect: directly model the 1st-oder RRS of the direct beam

Clouds: Lambertian + IPA, GOMECAT CTP, fc 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: SO2, NO2, BrO, HCHO NO2: PRATMO (stratosphere) + GEOS-CHEM (troposphere)

BrO: PRATMO (stratosphere) + well mixed in the troposphere SO2/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)

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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

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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%)

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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

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Comparison with Ozonesonde TCO

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Comparison with Ozonesonde TCO

GOME TCO captures most of the temporal variability in ozonesonde TCOMean biases: <3.3 DU (15%) at 30 stations1 : 3-8 DU (12-27%)

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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

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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

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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

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Summary and Future OutlookOzone 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 modelingRetrieval 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

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AcknowledgementsSupported by NASA and the Smithsonian InstitutionESA and DLRTOMS, SAGE, WOUDC, SHADOZ, CMDLNCEP, ECMWF, GEOS-CHEM, GOCART, PRATMOCluster machine and its support at Harvard-Smithsonian CFA

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High Resolution Solar Reference Spectrum

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Variable Slit/Wavelength Calibration Use GDP extraction software with all standard corrections Instrument slit function characterization (Chance, 1998)

Assume Gaussian, use non-linear least squares fitting High resolution solar reference spectrum (Caspar and Chance, 1998) Variable slit widths (21 spectral pixels in 5-pixel increments)

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Correction with Climatology/Observations

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Fitting Residuals

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Effects of Ozone Cross Sections on Retrievals

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Effects of Ozone Cross Sections on Retrievals

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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

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Informational Analysis --- DFS and A Priori Influence

DFS: 1.2 DFS in the tropics, 0.5 at high latitudesA Priori influence in TCO: 15% in the tropics, 50% at high-latitudes

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Error Analysis

Liu et al., 2005, JGR

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Comparison with Ozonesonde TCO

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Mean biases: <3.3 DU (15%) at 30 stations; 1 : 3-8 DU (12-27%) Improvements over a priori at most stations: either reduces MBs or 1 or increases the correlation

Comparison with Ozonesonde Tropospheric Column Ozone

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Comparison with Ozonesonde SCO

http://www.cmdl.noaa.gov/infodata/ftpdata.html

GOME SCO compares better with 1%-KI buffered than 2%-KI unbuffered by 11-16 DU.

Altitude-dependent total ozone normalization reduces the bias contrast and GOME/sonde biases mainly with 2%-KI unbuffered.

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Profile Comparison with Ozonesonde

Systematic biases

Large positive biases of (30-70%) at Carbon Iodine and most tropical stations

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Profile Comparison with Ozonesonde

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

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GOME vs. GEOS-CHEM

Similar overall structuresGlobal biases:

<2±4 DU, r=0.82-0.9 SH:

<1±2 DU,r=0.94-0.98 NH:

<4.3±4.6 DU, r=0.6-0.8

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GOME vs. GEOS-CHEM

Usually within 5 DU.

Large positive bias of 5-15 DU at some northern tropical and subtropical regions: central America, tropical North Africa, Southeast Asia, Middle East

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GOME vs. GEOS-CHEM & MOZAIC