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| Titel |
Depolarization ratio of polar stratospheric clouds in coastal Antarctica: comparison analysis between ground-based Micro Pulse Lidar and space-borne CALIOP observations |
| VerfasserIn |
C. Córdoba-Jabonero, J. L. Guerrero-Rascado, D. Toledo, M. Parrondo, M. Yela, M. Gil, H. A. Ochoa |
| 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 ; 6, no. 3 ; Nr. 6, no. 3 (2013-03-14), S.703-717 |
| Datensatznummer |
250017842
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| Publikation (Nr.) |
 copernicus.org/amt-6-703-2013.pdf |
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| Zusammenfassung |
| Polar stratospheric clouds (PSCs) play an important role in polar ozone
depletion, since they are involved in diverse ozone destruction processes
(chlorine activation, denitrification). The degree of that ozone reduction
is depending on the type of PSCs, and hence on their occurrence. Therefore
PSC characterization, mainly focused on PSC-type discrimination, is widely
demanded. The backscattering (R) and volume linear depolarization (δV) ratios are the parameters usually used in lidar measurements for PSC
detection and identification. In this work, an improved version of the
standard NASA/Micro Pulse Lidar (MPL-4), which includes a built-in
depolarization detection module, has been used for PSC observations above
the coastal Antarctic Belgrano II station (Argentina, 77.9° S 34.6° W, 256 m a.s.l.) since 2009. Examination of the
MPL-4 δV feature as a suitable index for PSC-type discrimination
is based on the analysis of the two-channel data, i.e., the parallel (p-) and
perpendicular (s-) polarized MPL signals. This study focuses on the
comparison of coincident δV-profiles as obtained from
ground-based MPL-4 measurements during three Antarctic winters with those
reported from the space-borne lidar CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) aboard the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) satellite in
the same period (83 simultaneous cases are analysed for 2009–2011 austral
winter times). Three different approaches are considered for the comparison
analysis between both lidar profile data sets in order to test the degree of
agreement: the correlation coefficient (CC), as a measure of the
relationship between both PSC vertical structures; the mean differences
together with their root mean square (RMS) values found between data sets;
and the percentage differences (BIAS), parameter also used in profiling
comparisons between CALIOP and other ground-based lidar systems. All of them
are examined as a function of the CALIPSO ground-track distance from the
Belgrano II station. Results represent a relatively good agreement between
both ground-based MPL-4 and space-borne CALIOP profiles of the volume linear
depolarization ratio δV for PSC events, once the MPL-4
depolarization calibration parameters are applied. Discrepancies between
CALIOP and MPL-4 profiles in vertical layering structure are enhanced from
20 km up, likely due to a decrease of the signal-to-noise ratio (SNR) for
both lidar systems at those altitudes. Regarding the results obtained from
the mean and the percentage differences found between MPL-4 and CALIOP
δV profiles, a predominance of negative values is also observed,
indicating a generalized underestimation of the MPL-4 depolarization as
compared to that reported by CALIOP. However, absolute differences between
those δV-profile data sets are no higher than a 10 ± 11%
in average. Moreover, the degree of agreement between both lidar
δV data sets is slightly dependent on the CALIPSO ground-track overpass
distance from the Belgrano II station. That is, small discrepancies are
found when CALIPSO ground-track distance is as close as far from the
ground-based station. These results would indicate that MPL-4 depolarization
observations would reflect relatively well the PSC field that CALIOP can
detect at relatively large distances from the ground-based station. As a
consequence, PSC properties can be statistically similar, on average, over
large volumes, and hence the present weak disagreement found between both
the lidar δV data sets can be likely dominated by small spatial
PSC inhomogeneities along the CALIPSO separation from the station. This
statement is based on the fact that Belgrano II is a station located well
inside the stable Antarctic polar vortex, allowing determined thermodynamic
conditions leading to a very low variability in the PSC field, and in
their properties. |
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