Xiong Liu

1

Direct Tropospheric Ozone Retrieval from GOME

• Xiong Liu
• Harvard-Smithsonian Center for Astrophysics
• xliu_at_cfa.harvard.edu
• December 20, 2004

2
Outline

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

3
Introduction

• Current tropospheric ozone retrievals are mainly
  based on the residual approaches limited to
  certain latitude ranges and to monthly level
• 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

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Variable Slit Widths and Shifts
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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

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Retrieval Characterization

• Averaging Kernel characterize the retrieval
• DFS diagonal elements of averaging kernels
• A priori influence

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Examples of Averaging Kernels
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Tropo. DFS May 1997
Trop. A Priori May 1997
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A Priori Influence (06/7-9/1997)
TOMS V8 A Priori
Retrieval with TOMS V8 A Priori
GEOS-CHEM A Priori
Retrieval with GEOS-CHEM A Priori
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Retrieval Errors
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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
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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.

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Stratospheric Column Ozone Comparison
Column ozone between tropopause to30-35 km
1-KI buffered
2-KI unbuffered
A Priori Retrieval Ozonesonde

• GOME-Ozonesonde
• Systematic differences exists at Carbon Iodine,
  CMDL, SHADOZ stations
• Bias lt3 DU (2), except at Ny Ålesund and
  Neumayer (-3.3 and 4.5)
• 1 ? 4-9 DU (4-6) in the tropics and 10-22 DU
  (5-10) at higher latitudes.

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Tropospheric Column Ozone Comparison
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Profile Hohenpeißenberg (48N,11E), 1996-1999

• The degradation is well handled
• GOME retrievals agree well with ozonesonde
• Biases lt2 DU (10)
• 1 ? lt10 DU (25)

A Priori Retrieval Ozonesonde
17
Profile America Samoa (14S,171W), 1996-1997

• Positive bias in the middle, negative bias at
  two ends, probably due to some systematic bias in
  radiance spectra and the wavelength dependent
  correction is not perfect.
• Biases lt 4 DU (40)
• 1 ? lt4 DU (30)
• Bias in tropospheric/stratospheric column ozone
  is reduced due to canceling errors.

A Priori Retrieval Ozonesonde
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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
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Monthly Mean Tropospheric Ozone (09/96-11/97)
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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
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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 profiles, stratospheric ozone, and
  tropospheric ozone compare well with ozonesonde
  observations except some stratospheric bias at
  Carbon Iodine stations, CMDL, and SHADOZ
  stations.
• 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.

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Future Work

• Complete tropospheric ozone retrieval for the
  8-year GOME data record and apply the algorithm
  to SCIMACHY and OMI data
• With the aid of GEOS-CHEM, other observations, or
  model fields, understand the GOME/GEOS-CHEM
  similarities and differences, and investigate
  global/regional distribution of tropospheric
  ozone.
• Tropospheric ozone radiative forcing
• Tropospheric/stratospheric ozone variability

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GOME vs. GEOS-CHEM Tropospheric Ozone
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GOME vs. GEOS-CHEM Tropospheric Ozone
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GOME vs. GEOS-CHEM Tropospheric Ozone
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GOME vs. GEOS-CHEM Tropospheric Ozone
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GOME vs. GEOS-CHEM Tropospheric Ozone