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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/amt-2020-266
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/amt-2020-266
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  17 Jul 2020

17 Jul 2020

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This preprint is currently under review for the journal AMT.

Retrieval of microphysical cloud parameters from EM-FTIR spectra measured in Arctic summer 2017

Philipp Richter1, Mathias Palm1, Christine Weinzierl1, Hannes Griesche2, Penny M. Rowe3, and Justus Notholt1 Philipp Richter et al.
  • 1University of Bremen, Institute of Environmental Physics, Otto-Hahn-Allee 1, 28359 Bremen, Germany
  • 2Leibniz Institute for Tropospheric Research (TROPOS), Permoserstr. 15, 04318 Leipzig, Germany
  • 3NorthWest Research Associates, Redmond, WA, USA

Abstract. Infrared spectral radiances of optically thin clouds show high sensitivity to changes of the microphysical cloud parameters. Therefore, measurements of infrared spectral radiance of clouds in the spectral range from 770.9 cm−1 to 1163.4 cm−1 using a mobile Fourier Transform Infrared spectrometer were performed on the German research vessel Polarstern in the Arctic in summer 2017.

A new retrieval for microphysical cloud parameters of optically thin clouds called Total Cloud Water retrieval, designed to retrieve cloud water optical depth τcw, total effective droplet radius rtotal and condensed water path CWP from infrared spectral radiances without the incorporation of spectral radiances in the far-infrared below 600cm−1, has been developed for application on radiances from the measurement campaign. Validation is performed against derived quantities from a combined cloud radar, lidar and microwave radiometer measurement synergy retrieval, called Cloudnet, performed by the Leibnitz Institute for Trospheric Research.

Applied to spectral radiances of synthetic testcases, Total Cloud Water retrieval shows a high ability to retrieve τcw with a correlation of |r| = 0.98, as well as to retrieve CWP with |r| = 0.95 and rtotal with |r| = 0.86. Using the dataset from the campaign, a comparison between CWP from Total Cloud Water retrieval and Cloudnet was performed and showed a correlation of |r| = 0.81. In conclusion, the comparison to artificial clouds and the validation using Cloudnet showed that Total Cloud Water retrieval is able to retrieve the condensed water path from clouds for optically thin clouds and makes it a useful complementation for thin clouds to existing microwave-based measurements.

Philipp Richter et al.

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Philipp Richter et al.

Model code and software

Total Cloud Water retrieval Philipp Richter https://doi.org/10.5281/zenodo.3948047

Philipp Richter et al.

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Latest update: 08 Aug 2020
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Short summary
Optically thin clouds containing low amounts of water are difficult to observe, but due to their frequent presence they have a non-neglectible impact on Earth's radiative budget. Here we present a retrieval for mixed-phase clouds from thermal-infared spectra, measured using a FTIR spectrometer. Even in situations where the atmospheric windows in the far-infrared are not applicable, cloud optical depths, effective droplet radii and water paths of mixed-phase clouds can be retrieved.
Optically thin clouds containing low amounts of water are difficult to observe, but due to their...
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