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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 8, issue 1 | Copyright
Atmos. Meas. Tech., 8, 237-266, 2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 12 Jan 2015

Research article | 12 Jan 2015

A depolarisation lidar-based method for the determination of liquid-cloud microphysical properties

D. P. Donovan1, H. Klein Baltink1, J. S. Henzing2, S. R. de Roode3, and A. P. Siebesma1,3 D. P. Donovan et al.
  • 1Royal Netherlands Meteorological Institute (KNMI), P.O. Box 201, 3730 AE, De Bilt, the Netherlands
  • 2Netherlands Organisation for Applied Scientific Research (TNO), Princetonlaan 6, Utrecht, the Netherlands
  • 3Technical University of Delft (TUD), Delft, the Netherlands

Abstract. 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 (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 (MC) 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 (LES) 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.

Publications Copernicus
Short summary
Stratocumulus clouds are important for weather and climate. They contain relatively little water but are optically thick enough to turn sunny days to grey and globally they have a strong impact on the Earth's energy budget. A new lidar (laser-radar) technique has been developed that is well suited for remotely measuring stratocumulus properties in the important cloud-based region. The technique can supply information that is difficult or impossible for other remote-sensing methods to provide.
Stratocumulus clouds are important for weather and climate. They contain relatively little water...