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Xiong Liu

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Title: Xiong Liu


1

2004 AGU Fall Meeting Direct Tropospheric Ozone
Retrieval from GOME
  • Xiong Liu
  • Harvard-Smithsonian Center for Astrophysics
  • xliu_at_cfa.harvard.edu
  • Kelly Chance, Christopher Sioris, Robert Spurr,
    Thomas Kurosu, Randall Martin, Mike Newchurch, PK
    Bhartia
  • San Franciso, CA
  • December 17, 2004

2
Outline
  • Introduction
  • Algorithm description
  • Intercomparison with Ozonesonde, TOMS, and Dobson
  • Global distribution of tropospheric ozone and
    comparison with GEOS-CHEM model results
  • Summary and future work

3
Introduction
  • GOME first nadir-viewing satellite instrument
    that allows direct tropospheric ozone retrieval
    from the space.
  • Several groups Munro et al., 1998 Hoogen et
    al., 1999 Hasekamp et al., 2001 van der A et
    al, 2002 Muller et al., 2003 Liu et al., 2004
    have developed ozone profile retrieval algorithms
    from GOME each of them demonstrates that limited
    tropospheric ozone information can be derived.
  • However, tropospheric ozone retrieval remains
    very challenging from GOME
  • Require accurate and consistent calibrations.
  • Need to fit the Huggins bands to high precision.
  • Tropospheric ozone is only 10 of total column
    ozone.

4
Algorithm Description
  • Inversion technique Optimal Estimation
  • Measurements 289-307 nm, 326-338 nm Spatial
    resolution 96080 km2
  • Perform detailed wavelength and radiometric
    calibrations
  • Derive variable slit widths and shifts between
    radiances/irradiances
  • Fit shifts between trace gas absorption
    cross-sections and radiances
  • Co-add adjacent pixels from 289-307 nm to reduce
    noise
  • Improve polarization correction using GOMECAL
    (www.knmi.nl/gome_fd/)
  • Perform undersampling correction with a
    high-resolution solar reference
  • Fit degradation for 289-307 nm on line in the
    retrieval
  • Use LIDORT to simulate radiances and weighting
    functions
  • Improve forward model simulation
  • On-line correction of Ring filling in of the
    solar and telluric absorption feature with
    first-order single scattering RRS model Sioris
    and Evans, 2002
  • Look-up table correction of polarization errors
    van Oss, personal comm.
  • Monthly-mean SAGE stratospheric aerosols Bauman
    et al., 2003
  • GEOS-CHEM tropospheric aerosols Martin et al.,
    2002

5
Algorithm Description
  • Improve forward model simulation (continue)
  • Brions ozone absorption cross-sections Brion et
    al., 1993
  • Daily ECMWF temperature profiles (www.ecmwf.int)
  • Daily NCEP/NCAR surface pressure
    (www.cdc.noaa.gov)
  • Cloud-top height from GOMECAT Kurosu et al.,
    1999
  • Cloud fraction derived at 370.2 nm with albedo
    database Kolemeijer et al.,2003
  • Wavelength dependent albedo (2-order polynomial)
    from 326-338 nm
  • A priori latitude and monthly dependent TOMS V8
    climatology (a priori and its variance) McPeters
    et al., 2003, AGU
  • Retrieval Grid 11 layers, almost the same as
    the Umkehr grid
  • Bottom 2-3 layers are modified by
    tropopause/surface pressure
  • Tropospheric column ozone is directly retrieved
  • State Vector 47 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 2 NO2 2 BrO 2
    SO2 1 internal scattering
  • Fitting residual 0.40 for band 1a, 0.17 for
    band 2b, 0.3 for both
  • Speed 17 hours on a 2GHz processor for one
    day, could be operational

6
Validation and Intercomparison
  • GOME data are collocated at 25 ozonesonde
    stations during 96-99.
  • Validate retrievals against TOMS V8,
    Dobson/Brewer total ozone, and ozonesonde.
  • Ozonesonde data mostly from WOUDC, and some from
    CMDL, SHADOZ, and NDSC.
  • Collocation criteria
  • Within 8 hours, 1.5 latitude and 500 km in
    longitude
  • Average all TOMS points within GOME footprint
  • Number of comparisons 4429, 952, and 1937 with
    TOMS, Dobson, and ozonesonde, respectively.

http//www.woudc.org http//croc.gsfc.nasa.giv/sh
adoz http//ndsc.ncep.noaa.gov
http//toms.gsfc.nasa.gov/ http//www.cmdl.noaa.go
v/infodata/ftpdata.html
7
Total Column Ozone Comparison
  • GOME-TOMS within retrieval uncertainties and
    saptiotemporal variability.
  • Biases lt3 DU except 3-8 DU at a few
    high-latitude stations
  • 1? 2-4 DU in the tropics, 4-11 DU at higher
    latitudes.

A Priori Retrieval Dobson
TOMS
  • GOME-Dobson within retrieval uncertainties and
    ozone variability.
  • Biases lt5 DU, and lt8 DU at two high-latitude
    stations
  • 1 ? 3-6 DU in the tropics, 6-19 DU at higher
    latitudes.

8
Tropospheric Column Ozone Comparison
9
Examples of Daily Global Tropospheric Ozone
Feb. 24-26, 1997
Low tropospheric ozone in tropical Pacific
Bands of high ozone at mid-latitudes
High ozone over biomass burning
South Atlantic Paradox
High ozone at high-latitudes during late winter
and early spring
Sep. 16-18, 1997
Sep. 1-3, 1997
10
Monthly Mean Tropospheric Ozone (09/96-10/97)
11
GOME vs. GEOS-CHEM Tropospheric Ozone
GOME
GEOS-CHEM
SON,96 R0.67 1.86.8DU
DJF,96-97 R0.83 0.05.3DU
MAM,97 R0.82 2.2 4.5DU
JJA,97 R0.64 2.5 5.7DU
12
Summary
  • Ozone profiles and tropospheric column ozone are
    derived from GOME using the optimal estimation
    approach after detailed treatments of wavelength
    and radiometric calibrations and improvement of
    forward model inputs.
  • Retrieved total ozone compares very well with
    TOMS and Dobson/Brewer total ozone.
  • The tropospheric column ozone compare well with
    ozonesonde measurements.
  • Global distribution of tropospheric ozone is
    presented. It clearly shows the signals due to
    biomass burning, air pollution,
    stratospheric-troposphere exchange, transport and
    convection.
  • The overall structures of retrieved tropospheric
    ozone are similar to those of GEOS-CHEM, but
    significant differences exist.

13
Future Work
  • Retrieve tropospheric ozone for the 8-year GOME
    data record and apply the algorithm to SCIMACHY
    data
  • With the aid of GEOS-CHEM, investigate
    global/regional distribution of tropospheric
    ozone and understand the GOME/GEOS-CHEM
    similarities and differences.
  • Tropospheric ozone radiative forcing
  • Tropospheric/stratospheric ozone variability
  • Acknowledgements
  • This study is supported by the NASA ACMAP and by
    Smithsonian Institution.
  • We thank WOUDC and its data providers, SHADOZ,
    CMDL, NDSC, TOMS, and M. Fujiwara for providing
    correlative measurements.
  • We are grateful to M. Fu and P.I. Palmer for
    providing the GEOS-CHEM model results.
  • We thank R. van Oss for providing look-up table
    and software for correcting radiance errors due
    to neglect polarization.
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