1 xiong liu harvard-smithsonian center for astrophysics k.v. chance, c.e. sioris, r.j.d. spurr, t.p....

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Xiong Liu

Harvard-Smithsonian Center for Astrophysicsxliu@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

Direct Tropospheric Ozone Retrieval from GOME

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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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2 2

( )a a

Kx Y S x x

MIN

Misfit Smooth and Regularization

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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 aerosolsDaily 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 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

Hohenpeisenberg (48N, 11E)

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Validation and Intercomparison

GOME-TOMS= -2.1 ± 7.1 DU

Lauder (45S, 170E)

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 IntercomparisonHohenpeisenberg (48N, 11E)

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Validation and IntercomparisonLauder (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?

Siddans, 2003

Assume GOME measurement errors and no other systematic errors, there are about 7-9 DFS from 260-340 nm region.

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What can we get now?

Average GOME/SHADOZ Bias DFS

Soebijanta, 2003

For most retrievals, the resolving length is about 10-12 km in 19-50 km, > 30 km in 0-20 km [Meijer et al., 2003]