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| Titel |
A Depolarisation lidar based method for the determination of liquid-cloud microphysical properties |
| VerfasserIn |
David Donovan, Henk Klein Baltink, Bas Henzing, Stephen de Roode, Pier Siebesma |
| 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 |
250105627
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| Publikation (Nr.) |
 EGU/EGU2015-5159.pdf |
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| Zusammenfassung |
| The fact that polarisation lidars measure a~depolarisation signal in liquid
clouds due to the occurrence of multiple-scattering is well-known. The degree
of measured depolarisation depends on the lidar characteristics
(e.g. wavelength and receiver field-of-view) as well as the cloud
macrophysical (e.g. cloud base altitude) and microphysical (e.g. effective
radius, liquid water content) properties. Efforts seeking to use
depolarisation information in a~quantitative manner to retrieve cloud
properties have been undertaken with, arguably, limited practical success. In
this work we present a~retrieval procedure applicable to clouds with
(quasi-)linear liquid water content (\text{LWC}) profiles and (quasi-)constant
cloud droplet number density in the cloud base region. Thus limiting the
applicability of the procedure allows us to reduce the cloud variables to two
parameters (namely the derivative of the liquid water content with height and
the extinction at a~fixed distance above cloud-base). This simplification, in
turn, allows us to employ a~fast and robust optimal-estimation inversion using
pre-computed look-up-tables produced using extensive lidar Monte-Carlo
multiple-scattering simulations. In this paper, we describe the theory behind
the inversion procedure and successfully apply it to simulated observations
based on large-eddy simulation model output. The inversion procedure is then
applied to actual depolarisation lidar data corresponding to a~range of cases
taken from the Cabauw measurement site in the central Netherlands. The lidar
results were then used to predict the corresponding cloud-base region radar
reflectivities. In non-drizzling condition, it was found that the lidar
inversion results can be used to predict the observed radar reflectivities
with an accuracy within the radar calibration uncertainty (2--3\,dBZ). This
result strongly supports the accuracy of the lidar inversion results. Results
of a~comparison between ground-based aerosol number concentration and
lidar-derived cloud droplet number densities are also presented and
discussed. The observed relationship between the two quantities is seen to be
consistent with the results of previous studies based on aircraft-based in
situ measurements. |
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