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| Titel |
Relationship between optical extinction and liquid water content in fogs |
| VerfasserIn |
C. Klein  , A. Dabas |
| 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 ; 7, no. 5 ; Nr. 7, no. 5 (2014-05-16), S.1277-1287 |
| Datensatznummer |
250115757
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| Publikation (Nr.) |
 copernicus.org/amt-7-1277-2014.pdf |
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| Zusammenfassung |
| Studies carried out in the late 1970s suggest that a simple linear relationship
exists in practice between the optical extinction in the thermal IR and the
liquid water content (LWC) in fogs. Such a relationship opens the
possibility to monitor the vertical profile of the LWC in fogs with a rather
simple backscatter lidar. Little is known on how the LWC varies as a
function of height and during the fog life cycle, so the new measurement
technique would help understand fog physics and provide valuable data for
improving the quality of fog forecasts. In this paper, the validity
of the linear relationship is revisited in the light of recent observations
of fog droplet size distributions measured with a combination of sensors
covering a large range of droplet radii. In particular, large droplets
(radius above 15 μm) are now detected, which was not the case in the late
1970s. The results confirm that the linear relationship still holds, at least for
the mostly radiative fogs observed during the campaign. The impact of the
precise value of the real and imaginary parts of the refractive index on the
coefficient of the linear relationship is also studied. The usual practice
considers that droplets are made of pure water. This assumption is probably valid
for big drops, but it may be questioned for small ones since droplets are formed
from condensation nuclei of highly variable chemical composition. The study
suggests that the precise nature of condensation nuclei will primarily affect
rather light fogs with small droplets and light liquid water contents. |
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