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| Titel |
Towards an automatic lidar cirrus cloud retrieval for climate studies |
| VerfasserIn |
E. G. Larroza, W. M. Nakaema, R. Bourayou, C. Hoareau, E. Landulfo, P. Keckhut |
| 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. 11 ; Nr. 6, no. 11 (2013-11-26), S.3197-3210 |
| Datensatznummer |
250085114
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| Publikation (Nr.) |
 copernicus.org/amt-6-3197-2013.pdf |
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| Zusammenfassung |
| This paper presents a methodology to calculate lidar ratios for distinct
cirrus clouds that has been developed and implemented for a site located in
the Southern Hemisphere. The cirrus cloud lidar data processing aims to
consider a large cloud variability and cirrus cloud monitoring through a
robust retrieval process. Among cirrus features estimates for complex
scenes that lidar systems can provide, we highlight cloud geometrical
information and extinction-to-backscatter ratio (known as lidar ratio or
LR). In general, direct information on cirrus cloud microphysics is difficult
to derive because LR depends on the presence of ice crystals and their
properties such as shape, size, composition and orientation of particles. An
iterative process to derive a stable LR value has been proposed. One of the
keys is to restrict the analysis to conditions allowing accurate multilayer
events. This method uses nonparametric statistical approaches to identify
stationary periods according to cloud features and variability.
Measurements performed in the region of the metropolitan city of São
Paulo (MSP) have been used to implement and test the methodology developed
for cirrus cloud characterization. Good results are represented by examining
specific cases with multilayer cirrus cloud occurrence. In addition to the
geometrical parameters obtained, cirrus LR values were calculated for a
single day ranging from 19 ± 01 sr to 74 ± 13 sr for 2 observed
layers. This large difference in LR can indicate a mixture of ice crystal
particles with different sizes and shapes in both layers of the cirrus
clouds. Trajectory analyses indicate that both of these cloud layers can be
associated with different air mass and should be considered as 2 distinct
clouds in climatology. |
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