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| Titel |
Microphysical properties of synoptic-scale polar stratospheric clouds: in situ measurements of unexpectedly large HNO3-containing particles in the Arctic vortex |
| VerfasserIn |
S. Molleker, S. Borrmann, H. Schlager, B. Luo, W. Frey, M. Klingebiel, R. Weigel, M. Ebert, V. Mitev, R. Matthey, W. Woiwode, H. Oelhaf, A. Dörnbrack, G. Stratmann, J.-U. Grooß, G. Günther, B. Vogel, R. Müller, M. Krämer, J. Meyer, F. Cairo |
| 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 ; 14, no. 19 ; Nr. 14, no. 19 (2014-10-14), S.10785-10801 |
| Datensatznummer |
250119098
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| Publikation (Nr.) |
 copernicus.org/acp-14-10785-2014.pdf |
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| Zusammenfassung |
| In January 2010 and December 2011, synoptic-scale polar stratospheric cloud
(PSC) fields were probed during seven flights of the high-altitude research
aircraft M-55 Geophysica within the RECONCILE (Reconciliation of
essential process parameters for an enhanced predictability of Arctic
stratospheric ozone loss and its climate interaction) and the ESSenCe
(ESSenCe: ESA Sounder Campaign) projects. Particle size distributions in a
diameter range between 0.46 and 40μm were recorded by four
different optical in situ instruments. Three of these particle instruments
are based on the detection of forward-scattered light by single particles.
The fourth instrument is a grayscale optical array imaging probe. Optical
particle diameters of up to 35μm were detected with particle
number densities and total particle volumes exceeding previous Arctic
measurements. Also, gas-phase and particle-bound NOy was
measured, as well as water vapor concentrations. The optical characteristics
of the clouds were measured by the remote sensing lidar MAL (Miniature
Aerosol Lidar) and by the in situ backscatter sonde MAS (Multiwavelength
Aerosol Scatterometer), showing the synoptic scale of the encountered PSCs.
The particle mode below 2μm in size diameter has been identified
as supercooled ternary solution (STS) droplets. The PSC particles in the size
range above 2μm in diameter are considered to consist of nitric
acid hydrates, and the particles' high HNO3 content was confirmed by
the NOy instrument. Assuming a particle composition of nitric acid
trihydrate (NAT), the optically measured size distributions result in
particle-phase HNO3 mixing ratios exceeding available stratospheric
values. Therefore the measurement uncertainties concerning probable
overestimations of measured particle sizes and volumes are discussed in
detail. We hypothesize that either a strong asphericity or an alternate
particle composition (e.g., water ice coated with NAT) could explain our
observations. In particular, with respect to the denitrification by
sedimentation of large HNO3-containing particles, generally
considered to be NAT, our new measurements raise questions concerning
composition, shape and nucleation pathways. Answering these would improve the
numerical simulation of PSC microphysical processes like cloud particle
formation, growth and denitrification, which is necessary for better
predictions of future polar ozone losses, especially under changing global
climate conditions. Generally, it seems that the occurrence of large NAT
particles – sometimes termed "NAT rocks" – are a regular feature of
synoptic-scale PSCs in the Arctic. |
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