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| Titel |
Radiative transfer simulations of PSC signatures measured by CRISTA-NF during the RECONCILE campaign in winter 2009/2010 |
| VerfasserIn |
Sabine Griessbach, Christoph Kalicinsky, Reinhold Spang, Lars Hoffmann, Rolf Müller, Friedhelm Olschewski, Wolfgang Woiwode, Hermann Oelhaf, Martin Riese, Cornelius Schiller, Wiebke Frey, Sergej Molleker, Stephan Borrmann, Valentin Mitev, Michael Volk, Elisabeth Hoesen, Silvia Genco, Marc von Hobe |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250072276
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| Zusammenfassung |
| In-situ particle measurements of polar stratospheric clouds (PSC) aboard the high altitude
research aircraft M55-Geophysica during the RECONCILE campaign showed particle
concentrations about one order of magnitude larger than proposed by Fahey et al. (Science,
2001) for nitric acid trihydrate (NAT) rocks. Here we use infrared (IR) limb spectra measured
by the airborne instrument Cryogenic Infrared Spectrometers and Telescopes for
the Atmosphere (CRISTA-NF) to derive more information on the PSC particles’
microphysical properties. We compare the measured IR spectra with radiative transfer
simulations accounting for scattering based on the in-situ measured particle size
distributions.
For the simulation of the IR spectra the atmospheric state was constrained by measured
atmospheric profiles of trace gases, so that the remaining signatures are mainly due to cloud
particles. Up to flight altitude temperature, pressure, and several trace gas profiles of the
in-situ measurements, made aboard the aircraft, were incorporated. Above flight altitude
ERA-interim and satellite data were employed.
The comparison of the measured IR spectra with simulated clear air spectra
confirmed that cloud particles were present. A comparison with simulated clouds of
different composition clearly showed that the PSCs at flight altitude did not contain
ice. The simulations also showed that a PSC layer of about 5 km thickness with a
size distribution as proposed by Fahey is not sufficient to reproduce the measured
spectra.
Successful simulations of the IR spectra required to take into account the very complex
cloud situation. Measurements indicated that tropospheric clouds were present and that the
PSC was not homogeneous. Simulations with complex cloud information and measured
particle size distribution generally showed a good agreement with the measurements
when assuming either an optically thick tropospheric cloud or an optically thin
tropospheric cloud combined with a PSC containing large particles only in the lowest
layer.
A prominent feature at 820 cm-1 can be used to identify NAT in IR spectra. In our
simulations this feature was generated only by small NAT particles. The measured
CRISTA-NF spectra exhibit a distinct feature, very similar but slightly shifted, at around
816 cm-1. We found that trace gases that have band centers around 820 cm-1 are not the
origin of this feature. Information from literature and calculations of extinction coefficients
and single scattering albedos indicate that this NAT feature may be shifted towards smaller
wave numbers when non-spherical particles instead of spherical particles are present. If the
non-sphericity of these particles can be confirmed, this might have implications for the
discrepancy between the measured and the proposed NAT rock particle size distributions. |
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