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| Titel |
Inference of cloud altitude and optical properties from MAX-DOAS measurements |
| VerfasserIn |
Jan-Marcus Nasse, Johannes Zielcke, Udo Frieß, Johannes Lampel, Gert König-Langlo, Ulrich Platt |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250107529
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| Publikation (Nr.) |
 EGU/EGU2015-7232.pdf |
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| Zusammenfassung |
| Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) is a widely used
technique for the detection of atmospheric trace gases, e.g. NO2, SO2, BrO, HCHO, but also
for the oxygen collision complex O4. The atmospheric distribution of the latter is
proportional to the square of the molecular oxygen concentration and thus well known. By
comparing measured O4 differential slant column densities (dSCDs) from MAX-DOAS
measurements with modeled ones, information on aerosol distributions and optical
properties, as well as on clouds can be obtained using an algorithm based on optimal
estimation.
Here the ability of MAX-DOAS observations to detect cloud altitude and cloud
optical properties of different cloud covers based on measurements of O4 will be
discussed. The analysis uses measurements made by a ship-borne instrument on
two cruises of the German research vessel Polarstern to the Antarctic Weddell Sea
from June to October 2013. During this time a broad range of cloud and aerosol
conditions was encountered, in particular persistent low cloud cover with a high optical
thickness.
Aerosol and particle extinction profiles were retrieved with temporal resolutions
of up to 15 minutes. For clouds at altitudes up to 2000 m the results show a very
good agreement with co-located measurements of a commercial ceilometer and
pictures from a cloud camera. Unless visibility was very poor due to fog, even rapid
changes in cloud altitude or cover could be detected by MAX-DOAS. These results
indicate that under homogeneous cloud cover an accurate retrieval of trace gas
vertical profiles can be possible despite the strong influence of clouds on atmospheric
light paths. We will discuss advantages and limitations of cloud detection with
MAX-DOAS, implications for the subsequent retrieval of trace gas profiles and the possible
use of external (ceilometer) data as a priori information for the profile retrieval
algorithm. |
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