Preprints
https://doi.org/10.5194/amt-2022-245
https://doi.org/10.5194/amt-2022-245
 
28 Sep 2022
28 Sep 2022
Status: this preprint is currently under review for the journal AMT.

High spatial resolution retrieval of cloud droplet size distribution from polarized observations of the cloudbow

Veronika Pörtge1, Tobias Kölling2, Anna Weber1, Lea Volkmer1, Claudia Emde1, Tobias Zinner1, and Bernhard Mayer1 Veronika Pörtge et al.
  • 1Meteorologisches Institut, Ludwig-Maximilians-Universität München, Munich, Germany
  • 2Max Planck Institute for Meteorology, Hamburg, Germany

Abstract. The cloud droplet size distribution is often described by a gamma distribution defined by the effective radius (reff) and the effective variance (veff). The effective radius is directly related to the cloud’s optical thickness which influences the radiative properties of a cloud. The effective variance affects, among other things, the evolution of precipitation. Both parameters can be retrieved from measurements of the cloudbow. The cloudbow or rainbow is an optical phenomenon, which forms by single scattering of radiation by liquid cloud droplets at the cloud edge. The polarized radiance of the cloudbow crucially depends on the cloud droplet size distribution. reff and veff can be retrieved by fitting model simulations (stored in a look-up table) to polarized cloudbow observations.

This study uses measurements from the wide-field polarization-sensitive camera of the LMU spectral imager system specMACS onboard the German research airplane HALO. Together with precise cloud geometry data derived by a stereographic method, a geolocalization of the observed clouds is possible. Observations of the same cloud from consecutive images are combined into one radiance measurement from multiple angles. Two case studies of trade wind cumulus clouds measured during the EUREC4A field campaign are presented and the cloudbow technique is demonstrated. The results are combined into maps of reff and veff with a spatial resolution of 100 m by 100 m and large coverage (across-track swath width: 8 km). The first case study shows a stratiform cloud deck with distinct patches of large effective radii up to 40 µm and a median effective variance of 0.12. The second case study consists of small cumulus clouds (diameters of approximately 2 km). The retrieved reff is 6.92 µm and veff is 0.07 (both median values).

Veronika Pörtge et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2022-245', Bastiaan van Diedenhoven, 20 Oct 2022
  • RC2: 'Comment on amt-2022-245', Anonymous Referee #1, 29 Oct 2022

Veronika Pörtge et al.

Veronika Pörtge et al.

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Short summary
In this work, we analyze polarized cloudbow observations of the airborne camera system specMACS to retrieve the cloud droplet size distribution, defined by the effective radius (reff) and the effective variance (veff). Two case studies of trade wind cumulus clouds measured during the EUREC4A field campaign are presented. The results are combined into maps of reff and veff with a very high spatial resolution (100 m by 100 m), that give new insights into the spatial distribution of the parameters.