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Volume 18, issue 7 | Copyright

Special issue: The ACRIDICON-CHUVA campaign to study deep convective clouds...

Special issue: ML-CIRRUS – the airborne experiment on natural cirrus...

Atmos. Chem. Phys., 18, 4439-4462, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 03 Apr 2018

Research article | 03 Apr 2018

Comparing airborne and satellite retrievals of cloud optical thickness and particle effective radius using a spectral radiance ratio technique: two case studies for cirrus and deep convective clouds

Trismono C. Krisna1, Manfred Wendisch1, André Ehrlich1, Evelyn Jäkel1, Frank Werner1,a, Ralf Weigel3,4, Stephan Borrmann3,4, Christoph Mahnke3, Ulrich Pöschl4, Meinrat O. Andreae4,6, Christiane Voigt2,3, and Luiz A. T. Machado5 Trismono C. Krisna et al.
  • 1Leipzig Institute for Meteorology, University of Leipzig, Leipzig, Germany
  • 2Institute of Atmospheric Physics, German Aerospace Center (DLR), Oberpfaffenhofen, Germany
  • 3Institute of Atmospheric Physics, Johannes Gutenberg University, Mainz, Germany
  • 4Biogeochemistry, Multiphase Chemistry, and Particle Chemistry Departments, Max Planck Institute for Chemistry (MPIC), Mainz, Germany
  • 5Center of Weather Forecast and Climates Studies, National Institute for Space Research, São José dos Campos, Brazil
  • 6Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA
  • anow at: Joint Center for Earth Systems Technology, University of Maryland, Baltimore, MD, USA

Abstract. Solar radiation reflected by cirrus and deep convective clouds (DCCs) was measured by the Spectral Modular Airborne Radiation Measurement System (SMART) installed on the German High Altitude and Long Range Research Aircraft (HALO) during the Mid-Latitude Cirrus (ML-CIRRUS) and the Aerosol, Cloud, Precipitation, and Radiation Interaction and Dynamic of Convective Clouds System – Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud Resolving Modelling and to the Global Precipitation Measurement (ACRIDICON-CHUVA) campaigns. On particular flights, HALO performed measurements closely collocated with overpasses of the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Aqua satellite. A cirrus cloud located above liquid water clouds and a DCC topped by an anvil cirrus are analyzed in this paper. Based on the nadir spectral upward radiance measured above the two clouds, the optical thickness τ and particle effective radius reff of the cirrus and DCC are retrieved using a radiance ratio technique, which considers the cloud thermodynamic phase, the vertical profile of cloud microphysical properties, the presence of multilayer clouds, and the heterogeneity of the surface albedo. For the cirrus case, the comparison of τ and reff retrieved on the basis of SMART and MODIS measurements yields a normalized mean absolute deviation of up to 1.2% for τ and 2.1% for reff. For the DCC case, deviations of up to 3.6% for τ and 6.2% for reff are obtained. The larger deviations in the DCC case are mainly attributed to the fast cloud evolution and three-dimensional (3-D) radiative effects. Measurements of spectral upward radiance at near-infrared wavelengths are employed to investigate the vertical profile of reff in the cirrus. The retrieved values of reff are compared with corresponding in situ measurements using a vertical weighting method. Compared to the MODIS observations, measurements of SMART provide more information on the vertical distribution of particle sizes, which allow reconstructing the profile of reff close to the cloud top. The comparison between retrieved and in situ reff yields a normalized mean absolute deviation, which ranges between 1.5 and 10.3%, and a robust correlation coefficient of 0.82.

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The optical thickness and particle effective radius of a cirrus above liquid water clouds and a DCC topped by an anvil cirrus are retrieved based on SMART and MODIS radiance measurements. For the cirrus, retrieved particle effective radius are validated with corresponding in situ data using a vertical weighting method. This approach allows to assess the measurements, retrieval algorithms, and derived cloud products.
The optical thickness and particle effective radius of a cirrus above liquid water clouds and a...