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| Titel |
Cloud and aerosol classification for 2.5 years of MAX-DOAS observations in Wuxi (China) and comparison to independent data sets |
| VerfasserIn |
Y. Wang, M. Penning de Vries, P. H. Xie, S. Beirle, S. Dörner, J. Remmers, A. Li, T. Wagner |
| 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 ; 8, no. 12 ; Nr. 8, no. 12 (2015-12-10), S.5133-5156 |
| Datensatznummer |
250116718
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| Publikation (Nr.) |
 copernicus.org/amt-8-5133-2015.pdf |
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| Zusammenfassung |
| Multi-axis differential optical absorption spectroscopy (MAX-DOAS)
observations of trace gases can be strongly influenced by clouds and
aerosols. Thus it is important to identify clouds and characterize their
properties. In a recent study Wagner et al. (2014) developed a cloud
classification scheme based on the MAX-DOAS measurements themselves with
which different "sky conditions" (e.g., clear sky, continuous clouds, broken
clouds) can be distinguished. Here we apply this scheme to long-term
MAX-DOAS measurements from 2011 to 2013 in Wuxi, China (31.57° N,
120.31° E). The original algorithm has been adapted to the
characteristics of the Wuxi instrument, and extended towards smaller solar
zenith angles (SZA). Moreover, a method for the determination and correction
of instrumental degradation is developed to avoid artificial trends of the
cloud classification results. We compared the results of the MAX-DOAS cloud
classification scheme to several independent measurements: aerosol optical
depth from a nearby Aerosol Robotic Network (AERONET) station and from two Moderate Resolution Imaging
Spectroradiometer (MODIS) instruments, visibility derived from a visibility meter and various cloud parameters from different satellite
instruments (MODIS, the Ozone Monitoring Instrument (OMI) and the Global Ozone Monitoring Experiment (GOME-2)). Here it should be noted that no
quantitative comparison between the MAX-DOAS results and the independent
data sets is possible, because (a) not exactly the same quantities are
measured, and (b) the spatial and temporal sampling is quite different. Thus
our comparison is performed in a semi-quantitative way: the MAX-DOAS cloud
classification results are studied as a function of the external quantities.
The most important findings from these comparisons are as follows: (1) most cases
characterized as clear sky with low or high aerosol load were associated
with the respective aerosol optical depth (AOD) ranges obtained by AERONET and MODIS; (2) the
observed dependences of MAX-DOAS results on cloud optical thickness and
effective cloud fraction from satellite confirm that the MAX-DOAS cloud
classification scheme is sensitive to cloud (optical) properties; (3) the
separation of cloudy scenes by cloud pressure shows that the MAX-DOAS cloud
classification scheme is also capable of detecting high clouds; (4) for some
cloud-free conditions, especially with high aerosol load, the coincident
satellite observations indicated optically thin and low clouds. This finding
indicates that the satellite cloud products contain valuable information on
aerosols. |
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