Intercomparison of tropospheric ozone measurements from TES and OMI

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Intercomparison of tropospheric ozone
measurements from TES and OMI a new method
using a chemical transport model as comparison
platform

• Lin Zhang, Daniel Jacob, Xiong Liu, Jennifer
  Logan, and the TES Science Team

Aura Science Team Meeting (Oct. 28, 2008)
Work supported by NASA Earth and Space Science
Fellowship
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Concurrent ozone measurements from IR and UV

• OMI
• Nadir-looking instrument measuring backscattered
  solar radiation (270-500 nm)
• Daily global coverage at a spatial resolution of
  13 x 24 km2 at nadir
• Retrieve ozone at 24 2.5 km layers

• TES
• Infrared-imaging Fourier transform spectrometer
  (3.3-15.4 µm)
• 16 orbits of nadir vertical profiles at a spatial
  resolution of 5x8 km2 and spaced 1.6 along the
  orbit track every other day.
• Retrievals of ozone and CO at 67 levels from
  surface up to 0.1 hPa, version 3 data

Do they provide consistent measurements of
tropospheric ozone? What can we learn by
comparing both measurements with chemical
transport models?
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Vertical sensitivity of TES and OMI ozone
retrievals
Both retrievals are obtained from the optimal
estimation method Rodgers, 2000
Averaging kernel
Degrees of Freedom for tropospheric ozone
OMI
July 2006
TES
Zonal average of Diagonal terms of AK
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Tropospheric ozone from TES and OMI
2006 ozone at 500 hPa averaged on 4ox5o resolution
OMI observations are selected along TES pixels.
The data are reprocessed with a single fixed a
priori.
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Tropospheric ozone from TES, OMI and GEOS-Chem
2006 ozone at 500 hPa averaged on 4ox5o resolution
The data and model results are reprocessed with a
single fixed a priori. GEOS-Chem simulation in
4ox5o resolution is sampled along the TES/OMI
pixels, and then smoothed by corresponding
averaging kernels.
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Validation with ozonesonde
Ozonesonde data from 2005-2007, available at AURA
AVDC Coincidence Criteria lt 2o longitudes
Latitudes, lt 10 hours
60oS-60oN, 500 hPa TES has a positive bias of
5.4 9 ppbv OMI has a positive bias of
3.1 5 ppbv
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Methods for the intercomparison
Sparse in time and space
Validation
Validation
1. Sonde method Validation with ozonesonde
measurements
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Methods for the intercomparison
Sparse in time and space
Validation
Validation
Direct comparison (Rodgers and Conner, 2003)
1. Sonde method Validation with ozonesonde
measurements 2. Direct method Compare OMI/TES
directly after considering their different a
priori constrains and vertical sensitivity (Apply
OMI averaging kernels to TES retrievals)
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Methods for the intercomparison
Sparse in time and space
Validation
Validation
Comparison
Comparison
Comparison
Direct comparison (Rodgers and Conner, 2003)
1. Sonde method Validation with ozonesonde
measurements 2. Direct method Compare OMI/TES
directly after considering their different a
priori constrains and vertical sensitivity (Apply
OMI averaging kernels to TES retrievals) 3. CTM
method Use GEOS-Chem CTM as a comparison
platform
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Methods for the intercomparison
Sparse in time and space
Validation
Validation
Evaluation
Interpretation
Evaluation
Evaluation
Interpretation
Interpretation
Direct comparison (Rodgers and Conner, 2003)
1. Sonde method Validation with ozonesonde
measurements 2. Direct method Compare OMI/TES
directly after considering their different a
priori constrains and vertical sensitivity (Apply
OMI averaging kernels to TES retrievals) 3. CTM
method Use GEOS-Chem CTM as a comparison
platform
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What do the methods actually compare?
Let

• Sonde method TES sonde/TES AK bTES
• OMI sonde/OMI AK bOMI
• TES OMI bTES bOMI

2. Direct method AOMIbTES bOMI AOMI(ATES
I)(X Xa)
(Rodgers and Conner, 2003)
3. CTM method (TES CTM/TES AK) (OMI
CMT/OMI AK) bTES bOMI (ATES
AOMI)(X XCTM)
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Quantify differences between TES and OMI
1. TES OMI (sonde) bTES bOMI
2. TES (OMI AK) OMI AOMIbTES bOMI
AOMI(ATES I)(X Xa)
3. TES OMI (GC) bTES bOMI (ATES
AOMI)(X XCTM)
500 hPa
76 TES/OMI/sonde coincidences for 2006
Direct method
CTM method
In the direct method, slopes lt 1 reflect
application of AOMI reduce the sensitivity to
diagnose the bias. The CTM method preserves the
variability of the differences in the comparison.
TES OMI Sonde method ppbv
850 hPa
CTM method
Direct method
TES OMI Sonde method ppbv
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Difference between TES and OMI at 500 hPa
Direct method
TES OMI
Sonde method
CTM method
2.6 6.6 ppbv
-0.1 3.6 ppbv
-0.3 5.0 ppbv
TES OMI Mean 1 sigma
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Difference between TES and OMI at 850 hPa
Direct method
TES OMI
Sonde method
CTM method
3.3 6.8 ppbv
-0.3 1.9 ppbv
2.7 5.5 ppbv
TES OMI Mean 1 sigma
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Differences with GEOS-Chem at 500 hPa
For 2006 and averaged on 4ox5o resolution
Minus 3 ppbv from both TES and OMI measurements.
Regions with the bias between TES and OMI larger
than 10 ppbv are masked as black.
GC sonde
GC/TES AK (TES 3)
GC/OMI AK (OMI 3)
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Differences with GEOS-Chem at 500 hPa
For 2006 and averaged on 4ox5o resolution
Minus 3 ppbv from both TES and OMI measurements.
Regions with the bias between TES and OMI larger
than 10 ppbv are masked as black.
GC sonde
GC/TES AK (TES 3)
GC/OMI AK (OMI 3)
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Extra
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Tropospheric ozone measurements from TES and OMI
2006 ozone at 500 hPa averaged on 4ox5o resolution
OMI observations are sampled along the TES
pixels. Convert the different a priori to a fixed
a priori
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Examples of clear-sky Averaging Kernels
15N
40N
60N
(a) TES (67 levels) (b) OMI (24
layers)