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
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
Do they provide consistent measurements of tropospheric ozone?
What can we learn by comparing both measurements with chemical transport models?
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
Vertical sensitivity of TES and OMI ozone retrievals
July 2006 Degrees of Freedom for tropospheric ozone
Zonal average of Diagonal terms of AK
Averaging kernel
Both retrievals are obtained from the optimal estimation method [Rodgers, 2000]:
OMITES
Tropospheric ozone from TES and OMI
OMI observations are selected along TES pixels. The data are reprocessed with a single fixed a priori.
2006 ozone at 500 hPa averaged on 4ox5o resolution
Tropospheric ozone from TES, OMI and GEOS-Chem
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.
2006 ozone at 500 hPa averaged on 4ox5o resolution
Ozonesonde data from 2005-2007, available at AURA AVDC
Coincidence Criteria: < 2o longitudes & Latitudes, < 10 hours
Validation with ozonesonde
60oS-60oN, 500 hPa:
TES has a positive bias of 5.4 ± 9 ppbv
OMI has a positive bias of 3.1 ± 5 ppbv
Methods for the intercomparison
Sparse in time and space
Validation Validation
1. Sonde method: Validation with ozonesonde measurements
Methods for the intercomparison
Sparse in time and space
Validation Validation
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)
Direct comparison (Rodgers and Conner, 2003)
Methods for the intercomparison
Sparse in time and space
Validation Validation
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
Comparison Comparison
Comparison
Direct comparison (Rodgers and Conner, 2003)
Methods for the intercomparison
Sparse in time and space
Validation Validation
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
Evaluation Evaluation
Interpretation Interpretation
Evaluation Interpretation
Direct comparison (Rodgers and Conner, 2003)
What do the methods actually compare?
1. 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)
3. CTM method: (TES – CTM/TES AK) – (OMI – CMT/OMI AK)
= bTES – bOMI + (ATES – AOMI)(X – XCTM)
Let
(Rodgers and Conner, 2003)
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)
76 TES/OMI/sonde coincidences for 2006
500 hPa
850 hPa
In the direct method, slopes < 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]
TES – OMI Sonde method [ppbv]
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Difference between TES and OMI at 500 hPa
2.6 ± 6.6 ppbv -0.1 ± 3.6 ppbv -0.3 ± 5.0 ppbvTES – OMI Mean ± 1 sigma
Sonde method Direct method CTM methodTES – OMI
Difference between TES and OMI at 850 hPa
3.3 ± 6.8 ppbv -0.3 ± 1.9 ppbv 2.7 ± 5.5 ppbvTES – OMI Mean ± 1 sigma
Sonde method Direct method CTM methodTES – OMI
Differences with GEOS-Chem at 500 hPa
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.
For 2006 and averaged on 4ox5o resolution
GC – sonde GC/TES AK – (TES– 3) GC/OMI AK – (OMI– 3)
Differences with GEOS-Chem at 500 hPa
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.
For 2006 and averaged on 4ox5o resolution
GC – sonde GC/TES AK – (TES– 3) GC/OMI AK – (OMI– 3)
Extra
2006 ozone at 500 hPa averaged on 4ox5o resolution
Tropospheric ozone measurements from TES and OMI
OMI observations are sampled along the TES pixels.
Convert the different a priori to a fixed a priori: ( )( )aa XXAIXX −′−+=′ ˆˆ
Examples of clear-sky Averaging Kernels
(a) TES (67 levels)
(b) OMI (24 layers)
15°N 40°N 60°N