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| Titel |
MIPAS detection of cloud and aerosol particle occurrence in the UTLS with comparison to HIRDLS and CALIOP |
| VerfasserIn |
H. Sembhi, J. Remedios, T. Trent, D. P. Moore, R. Spang, S. Massie, J.-P. Vernier |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 5, no. 10 ; Nr. 5, no. 10 (2012-10-26), S.2537-2553 |
| Datensatznummer |
250003132
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| Publikation (Nr.) |
 copernicus.org/amt-5-2537-2012.pdf |
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| Zusammenfassung |
Satellite infrared emission instruments require efficient systems that can
separate and flag observations which are affected by clouds and aerosols.
This paper investigates the identification of cloud and aerosols from
infrared, limb sounding spectra that were recorded by the Michelson
Interferometer for Passive Atmospheric Sounding (MIPAS), a high spectral
resolution Fourier transform spectrometer on the European Space Agency's
(ESA) ENVISAT (Now inoperative since April 2012 due to loss of contact). Specifically, the performance of an existing cloud and
aerosol particle detection method is simulated with a radiative transfer
model in order to establish, for the first time, confident detection limits
for particle presence in the atmosphere from MIPAS data. The newly
established thresholds improve confidence in the ability to detect particle
injection events, plume transport in the upper troposphere and lower
stratosphere (UTLS) and better characterise cloud distributions utilising MIPAS
spectra. The method also provides a fast front-end detection system for the
MIPClouds processor; a processor designed for the retrieval of macro- and
microphysical cloud properties from the MIPAS data.
It is shown that across much of the stratosphere, the threshold for the
standard cloud index in band A is 5.0 although threshold values of over 6.0
occur in restricted regimes. Polar regions show a surprising degree of
uncertainty at altitudes above 20 km, potentially due to changing
stratospheric trace gas concentrations in polar vortex conditions and poor
signal-to-noise due to cold atmospheric temperatures. The optimised
thresholds of this study can be used for much of the time, but
time/composition-dependent thresholds are recommended for MIPAS data for the
strongly perturbed polar stratosphere. In the UT, a threshold of 5.0 applies
at 12 km and above but decreases rapidly at lower altitudes. The new
thresholds are shown to allow much more sensitive detection of particle
distributions in the UTLS, with extinction detection limits above 13 km
often better than 10−4 km−1, with values approaching 10−5 km−1 in some cases.
Comparisons of the new MIPAS results with cloud data from HIRDLS and CALIOP,
outside of the poles, establish a good agreement in distributions (cloud and
aerosol top heights and occurrence frequencies) with an offset between MIPAS
and the other instruments of 0.5 km to 1 km between 12 km and 20 km,
consistent with vertical oversampling of extended cloud layers within the
MIPAS field of view. We conclude that infrared limb sounders provide a very
consistent picture of particles in the UTLS, allowing detection limits which
are consistent with the lidar observations. Investigations of MIPAS data for
the Mount Kasatochi volcanic eruption on the Aleutian Islands and the Black
Saturday fires in Australia are used to exemplify how useful MIPAS limb
sounding data were for monitoring aerosol injections into the UTLS. It is
shown that the new thresholds allowed such events to be much more
effectively derived from MIPAS with detection limits for these case studies
of 1 × 10−5 km−1 at a wavelength of 12 μm. |
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