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| Titel |
Global distributions of nitric acid from IASI/MetOP measurements |
| VerfasserIn |
C. Wespes, D. Hurtmans, C. Clerbaux, M. L. Santee, R. V. Martin, P. F. Coheur |
| 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 ; 9, no. 20 ; Nr. 9, no. 20 (2009-10-22), S.7949-7962 |
| Datensatznummer |
250007702
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| Publikation (Nr.) |
 copernicus.org/acp-9-7949-2009.pdf |
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| Zusammenfassung |
| This paper presents the first global distributions of HNO3 total
columns acquired by the Infrared Atmospheric Sounding Interferometer (IASI)
instrument, launched onboard the MetOp platform in October 2006. IASI is an
infrared nadir-looking Fourier transform spectrometer providing atmospheric
radiance spectra at 0.5 cm−1 spectral resolution, from which
temperature and infrared absorbing gas concentration profiles are retrieved
with global Earth coverage twice a day. A first analysis of the IASI
measurements in terms of information content demonstrates the possibility of
retrieving a total column for HNO3 at all latitudes with a maximal
sensitivity in the middle stratosphere. The retrievals are performed from
IASI spectra in the atmospheric window using a fast radiative transfer model
and inversion software (FORLI) relying on the Optimal Estimation Method. The
operational processing of HNO3 total columns is achieved since March
2008. We show that FORLI-HNO3 performs well at all latitudes (RMS of
the spectral residuals around 2.3×10−6 W/m2 sr m−1)
and provides HNO3 total columns with on average statistical errors of
about 12%, reaching the threshold value of 32% at the equatorial belt.
The global distributions of the retrieved total columns for one year (from
March 2008 to February 2009) are presented and discussed with emphasis given
to seasonal and interhemispheric variations. Local seasonal variations at 6
specific locations are also described and discussed in comparison with MLS
volume mixing ratios at 46.5 hPa. The seasonal cycle observed in Polar
regions is highlighted, with maxima observed in fall-winter and minima
during spring-summer. The denitrification inside the Antarctic polar vortex
during winter is clearly revealed with unprecedented horizontal resolution:
HNO3 columns decreasing down to about 1×1016 molecules cm−2
are observed, which is consistent with the lower values of temperature
observed between 50 and 15 hPa (~20–25 km) and the resulting formation
and sedimentation of polar stratospheric clouds. During the same period, the
collar region of high quantities of HNO3 at the vortex edge is also
observed around 65–60° S latitude. Preliminary correlations between IASI
derived HNO3 and O3 columns inside the polar vortex are presented
and discussed. |
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