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| Titel |
The ASSET intercomparison of ozone analyses: method and first results |
| VerfasserIn |
A. J. Geer, W. A. Lahoz, S. Bekki, N. Bormann, Q. Errera, H. J. Eskes, D. Fonteyn, D. R. Jackson, M. N. Juckes, S. Massart, V.-H. Peuch, S. Rharmili, A. Segers |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 6, no. 12 ; Nr. 6, no. 12 (2006-12-05), S.5445-5474 |
| Datensatznummer |
250004197
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| Publikation (Nr.) |
 copernicus.org/acp-6-5445-2006.pdf |
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| Zusammenfassung |
This paper aims to summarise the current
performance of ozone data assimilation (DA) systems, to show where they can be
improved, and to quantify their errors. It examines 11 sets of ozone
analyses from 7 different DA systems. Two are numerical weather
prediction (NWP) systems based on general circulation models (GCMs); the
other five use chemistry transport models (CTMs). The systems examined
contain either linearised or detailed ozone chemistry, or no chemistry at
all. In most analyses, MIPAS (Michelson
Interferometer for Passive Atmospheric Sounding) ozone data are assimilated;
two assimilate SCIAMACHY (Scanning Imaging Absorption Spectrometer
for Atmospheric Chartography) observations instead.
Analyses are compared to independent ozone observations covering the
troposphere, stratosphere and lower mesosphere during the period July to
November 2003.
Biases and standard deviations are largest, and show the largest divergence
between systems, in the troposphere, in the
upper-troposphere/lower-stratosphere, in the upper-stratosphere and
mesosphere, and the Antarctic ozone hole region. However, in any particular
area, apart from the troposphere, at least one system can be found that
agrees well with independent data. In general, none of the differences can be
linked to the assimilation technique (Kalman filter, three or four
dimensional variational methods, direct inversion) or the system (CTM or NWP
system). Where results diverge, a main explanation is the way ozone is
modelled. It is important to correctly model transport at the tropical
tropopause, to avoid positive biases and excessive structure in the ozone
field. In the southern hemisphere ozone hole, only the analyses which
correctly model heterogeneous ozone depletion are able to reproduce the
near-complete ozone destruction over the pole. In the upper-stratosphere and
mesosphere (above 5 hPa), some ozone photochemistry schemes caused large but
easily remedied biases. The diurnal cycle of ozone in the mesosphere is not
captured, except by the one system that includes a detailed treatment of
mesospheric chemistry. These results indicate that when good observations are
available for assimilation, the first priority for improving ozone DA systems
is to improve the models.
The analyses benefit strongly from the good quality of the MIPAS ozone
observations. Using the analyses as a transfer standard, it is seen that
MIPAS is ~5% higher than HALOE (Halogen Occultation Experiment) in the
mid and upper stratosphere and mesosphere (above 30 hPa), and of order 10%
higher than ozonesonde and HALOE in the lower stratosphere (100 hPa to
30 hPa). Analyses based on SCIAMACHY total column are almost as good as the
MIPAS analyses; analyses based on SCIAMACHY limb profiles are worse in some
areas, due to problems in the SCIAMACHY retrievals. |
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