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Volume 16, issue 12
Atmos. Chem. Phys., 16, 7681–7693, 2016
https://doi.org/10.5194/acp-16-7681-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 16, 7681–7693, 2016
https://doi.org/10.5194/acp-16-7681-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 23 Jun 2016

Research article | 23 Jun 2016

Spectral optical layer properties of cirrus from collocated airborne measurements and simulations

Fanny Finger1,a, Frank Werner1,2, Marcus Klingebiel3,b, André Ehrlich1, Evelyn Jäkel1, Matthias Voigt3, Stephan Borrmann3,4, Peter Spichtinger3, and Manfred Wendisch1 Fanny Finger et al.
  • 1Leipzig Institute for Meteorology (LIM), University of Leipzig, Leipzig, Germany
  • 2University of Maryland (UMBC), Physics Department, Baltimore, Maryland, USA
  • 3Institute for Atmospheric Physics, Johannes Gutenberg University Mainz, Mainz, Germany
  • 4Max Planck Institute for Chemistry, Mainz, Germany
  • anow at: Dr. Födisch Umweltmesstechnik AG, Markranstädt, Germany
  • bnow at: Max Planck Institute for Meteorology, Hamburg, Germany

Abstract. Spectral upward and downward solar irradiances from vertically collocated measurements above and below a cirrus layer are used to derive cirrus optical layer properties such as spectral transmissivity, absorptivity, reflectivity, and cloud top albedo. The radiation measurements are complemented by in situ cirrus crystal size distribution measurements and radiative transfer simulations based on the microphysical data. The close collocation of the radiative and microphysical measurements, above, beneath, and inside the cirrus, is accomplished by using a research aircraft (Learjet 35A) in tandem with the towed sensor platform AIRTOSS (AIRcraft TOwed Sensor Shuttle). AIRTOSS can be released from and retracted back to the research aircraft by means of a cable up to a distance of 4 km. Data were collected from two field campaigns over the North Sea and the Baltic Sea in spring and late summer 2013. One measurement flight over the North Sea proved to be exemplary, and as such the results are used to illustrate the benefits of collocated sampling. The radiative transfer simulations were applied to quantify the impact of cloud particle properties such as crystal shape, effective radius reff, and optical thickness τ on cirrus spectral optical layer properties. Furthermore, the radiative effects of low-level, liquid water (warm) clouds as frequently observed beneath the cirrus are evaluated. They may cause changes in the radiative forcing of the cirrus by a factor of 2. When low-level clouds below the cirrus are not taken into account, the radiative cooling effect (caused by reflection of solar radiation) due to the cirrus in the solar (shortwave) spectral range is significantly overestimated.

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Solar spectra of optical layer properties of cirrus have been derived from the first truly collocated airborne radiation measurements using an aircraft and a towed sensor platform. The measured layer properties differ slightly due to horizontal cirrus inhomogeneities and the influence of low-level water clouds. Applying a 1-D radiative transfer model sensitivity studies were performed. It was found that if a low-level cloud is not considered, the solar cooling of the cirrus is strongly overestimated.
Solar spectra of optical layer properties of cirrus have been derived from the first truly...
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