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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 12, issue 3
Atmos. Meas. Tech., 12, 1635-1658, 2019
https://doi.org/10.5194/amt-12-1635-2019
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
Atmos. Meas. Tech., 12, 1635-1658, 2019
https://doi.org/10.5194/amt-12-1635-2019
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 13 Mar 2019

Research article | 13 Mar 2019

Improvement of airborne retrievals of cloud droplet number concentration of trade wind cumulus using a synergetic approach

Kevin Wolf1, André Ehrlich1, Marek Jacob2, Susanne Crewell2, Martin Wirth3, and Manfred Wendisch1 Kevin Wolf et al.
  • 1Leipzig Institute for Meteorology, University of Leipzig, Leipzig, Germany
  • 2Institute for Geophysics and Meteorology, University of Cologne, Cologne, Germany
  • 3Institute of Atmospheric Physics, German Aerospace Center, Oberpfaffenhofen, Germany

Abstract. In situ measurements of cloud droplet number concentration N are limited by the sampled cloud volume. Satellite retrievals of N suffer from inherent uncertainties, spatial averaging, and retrieval problems arising from the commonly assumed strictly adiabatic vertical profiles of cloud properties. To improve retrievals of N it is suggested in this paper to use a synergetic combination of passive and active airborne remote sensing measurement, to reduce the uncertainty of N retrievals, and to bridge the gap between in situ cloud sampling and global averaging. For this purpose, spectral solar radiation measurements above shallow trade wind cumulus were combined with passive microwave and active radar and lidar observations carried out during the second Next Generation Remote Sensing for Validation Studies (NARVAL-II) campaign with the High Altitude and Long Range Research Aircraft (HALO) in August 2016. The common technique to retrieve N is refined by including combined measurements and retrievals of cloud optical thickness τ, liquid water path (LWP), cloud droplet effective radius reff, and cloud base and top altitude. Three approaches are tested and applied to synthetic measurements and two cloud scenarios observed during NARVAL-II. Using the new combined retrieval technique, errors in N due to the adiabatic assumption have been reduced significantly.

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Using passive spectral solar radiation and active lidar, radar, and microwave measurements with HALO during NARVAL-II, the cloud droplet number concentration of shallow trade wind cumulus is estimated. With stepwise inclusion of the different instruments into the retrieval, the benefits of the synergetic approach based on artificial measurements and two cloud cases are demonstrated. Significant improvement with the synergetic method compared to the solar-radiation-only method is reported.
Using passive spectral solar radiation and active lidar, radar, and microwave measurements with...
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