Xiong Liu

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Direct Tropospheric Ozone Retrieval from GOME

• Xiong Liu
• Harvard-Smithsonian Center for Astrophysics
• xliu_at_cfa.harvard.edu
• K.V. Chance, C.E. Sioris, R.J.D. Spurr, T.P.
  Kurosu, R.V. Martin, M.J. Newchurch, P.K. Bhartia
• August 3, 2004

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Outline

• Introduction
• Retrieval Approach
• Validation with DOBSON, Ozonesonde, and TOMS
• Global Distribution of Tropospheric Ozone
• Future Directions

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Satellite-based Tropospheric Ozone Retrieval

• Satellite observations are crucial for studying
  the global distributions, spatial and temporal
  variability, sources and sinks, transport,
  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

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Retrieval Approach

• Optimal Estimation
• Measurements
• GOME Channel 1a 290-307 nm
• Spatial resolution 960 km x 80 km or 240 km x
  40 km
• Wavelength and radiometric calibrations
• Derive variable slit widths and shifts between
  radiances/irradiances
• Fitting shifts between trace gas absorption
  cross-sections and radiances
• On-line correction of Ring filling in of the
  solar and telluric absorption features
• Improved polarization correction using GOMECAL
• Undersampling correction

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Retrieval Approach

• 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,
  where has minimal absorption
• A priori
• TOMS V8 climatology TOMS EP monthly mean total
  ozone
• Assume a correlation length of 5 km to construct
  a priori covariance matrix from climatological
  variances
• 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

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Validation and Intercomparison
Hohenpeisenberg (48N, 11E)

• Comparison with TOMSV8 and DOBSON Total Ozone,
  Ozonesonde Observation
• GOME observations are 8 hours and 600 km within
  ozonesonde/DOBSON observation
• TOMS total ozone columns within GOME footprint
  are averaged

GOME-TOMS 0.3 5.9 DU
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Validation and Intercomparison
Lauder (45S, 170E)
GOME-TOMS -2.1 7.1 DU

• The average biases are within 3 DU with standard
  deviation within the range of ozone variability,
  retrieval and measurement uncertainties.

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Validation and Intercomparison
Hohenpeisenberg (48N, 11E)
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Validation and Intercomparison
Lauder (45S, 170E)
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Global Distribution of Tropospheric Ozone
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Tropospheric Ozone (09/04/97-09/15/97)
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Summary and Future Plans

• Ozone profiles and tropospheric ozone columns 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 well with TOMS and
  DOBSON total ozone.
• The profiles, stratospheric ozone, and
  tropospheric ozone compare well with ozonesonde
  observation. The average bias is within 3 DU with
  standard deviation within the uncertainties of
  measurements and ozone variability.
• Future Plan
• Tropospheric ozone retrieval from SCIAMACHY
  during the INTEX period and area.
• Improve retrieval including channel 2
• Tropospheric ozone assimilation and simulation

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Cross Section of Retrieved Ozone Profiles
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Global Distribution of Stratospheric Ozone
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Stratospheric Ozone (09/04/97-09/15/97)
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Global Distribution of Total Ozone
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Total Ozone (09/04/97-09/15/97)
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What do we expect from GOME?
Assume GOME measurement errors and no other
systematic errors, there are about 7-9 DFS from
260-340 nm region.
Siddans, 2003
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What can we get now?
For most retrievals, the resolving length is
about 10-12 km in 19-50 km, gt 30 km in 0-20 km
Meijer et al., 2003
Average GOME/SHADOZ Bias
DFS
Soebijanta, 2003