Improved GOMOS/Envisat ozone retrievals in the upper troposphere and the lower stratosphere
Global Ozone Monitoring by Occultation of Stars (GOMOS) on board Envisat has performed about 440 000 nighttime occultations during 2002–2012. Self-calibrating measurement principle, good vertical resolution, excellent pointing accuracy, and the wide vertical range from the troposphere up to the lowe...
| Main Authors: | , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-01-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | http://www.atmos-meas-tech.net/10/231/2017/amt-10-231-2017.pdf |
| Summary: | Global Ozone Monitoring by Occultation of Stars (GOMOS)
on board Envisat has performed about 440 000 nighttime occultations during
2002–2012. Self-calibrating measurement principle, good vertical
resolution, excellent pointing accuracy, and the wide vertical range from the
troposphere up to the lower thermosphere make GOMOS profiles interesting for
different analyses.
<br><br>
The GOMOS ozone data are of high quality in the stratosphere and the
mesosphere, but the current operational retrieval algorithm (IPF v6) is not
optimized for retrievals in the upper troposphere–lower stratosphere
(UTLS). In particular, validation of GOMOS profiles against ozonesonde data
has revealed a substantial positive bias (up to 100 %) in the UTLS region.
The retrievals in the UTLS are challenging because of low signal-to-noise
ratio and the presence of clouds.
<br><br>
In this work, we discuss the reasons for the systematic uncertainties in the
UTLS with the IPF v6 algorithm or its modifications based on simultaneous
retrievals of several constituents using the full visible wavelength range.
The main reason is high sensitivity of the UTLS retrieval algorithms to an
assumed aerosol extinction model.
<br><br>
We have developed a new ozone profile inversion algorithm for GOMOS data
(ALGOM2s version 1.0), which is optimized in the UTLS and uses IPF v6
advantages in the middle atmosphere. The ozone retrievals in the whole
altitude range from the troposphere to the lower thermosphere are performed
in two steps, as in the operational algorithm: spectral inversion followed
by the vertical inversion. The spectral inversion is enhanced by using a
DOAS-type method at visible wavelengths for the UTLS region. This method
uses minimal assumptions about the atmospheric profiles. The vertical
inversion is performed as in IPF v6 with the Tikhonov-type regularization
according to the target resolution.
<br><br>
The validation of new retrieved ozone profiles with ozonesondes shows a
dramatic reduction of GOMOS ozone biases in the UTLS. The new GOMOS ozone
profiles are also in a very good agreement with measurements by MIPAS,
ACE-FTS, and OSIRIS satellite instruments in the UTLS. It is also shown that
the known geophysical phenomena in the UTLS ozone are well reproduced with
the new GOMOS data. |
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| ISSN: | 1867-1381 1867-8548 |