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| Titel |
Polar Stratospheric Cloud Composition Studies Using CALIPSO Data |
| VerfasserIn |
Michael Pitts, Lamont Poole, Larry Thomason |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250033298
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| Zusammenfassung |
| After more than two decades of study, much has been learned about polar stratospheric
clouds (PSCs) and how they perturb stratospheric chemical cycles and catalyze ozone
depletion. However, the observational database of PSCs is actually relatively sparse and there
is still considerable uncertainty in their formation mechanisms. With the advent of the
Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO)
mission in 2006, new insight into PSC morphology is becoming available. The
polarization-sensitive CALIOP (Cloud-Aerosol LIdar with Orthogonal Polarization) lidar
system onboard the CALIPSO spacecraft is acquiring, on average, over 300,000 profiles
per day at latitudes poleward of 55o (including the polar night region up to 82o),
providing a unique opportunity for PSC studies. Our second-generation CALIPSO PSC
algorithm utilizes both the CALIOP 532-nm scattering ratio (ratio of total to molecular
backscatter coefficients) and 532-nm perpendicular backscatter coefficient for cloud
detection and an innovative successive horizontal averaging scheme which enables
the detection of strongly backscattering PSCs at fine (5-km) resolution and more
tenuous clouds at increasingly coarser scales. Including the perpendicular backscatter
measurements enhances the detection of tenuous PSC mixtures containing solid
particles (presumably nitric acid trihydrate, or NAT) in low number densities. In
addition, we have implemented a scheme for classifying PSCs by composition in
terms of their ensemble backscatter and depolarization in a manner analogous to
that used in previous ground-based and airborne lidar studies. Based on optical
model calculations for mixtures of liquid aerosol droplets with oblate NAT or ice
spheroids, we have defined four CALIOP-based PSC composition classes: supercooled
ternary solution (STS), ice, Mix1, and Mix2, with the latter two denoting mixtures of
liquid aerosol with NAT particles in lower or higher number densities/volumes,
respectively.
In this paper, we present example results for PSC coverage and composition for the four
Antarctic and Arctic seasons probed by CALIOP to date, illustrating interannual variability in
PSC areal coverage and the well-known contrast between the Antarctic and Arctic. We also
show distinctive seasonal and altitudinal variations in Antarctic PSC composition, which can
be related to changes in HNO3 and H2O observed by the Microwave Limb Sounder on the
Aura satellite. Finally, we explore potential NAT PSC nucleation mechanisms through
example case studies of CALIOP data using a PSC microphysics/optics model.
Examples from the recent RECONCILE field campaign will be shown if available. |
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