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

Atmospheric Chemistry and Physics. 2016;16(12):7681-7693 DOI 10.5194/acp-16-7681-2016

 

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Journal Title: Atmospheric Chemistry and Physics

ISSN: 1680-7316 (Print); 1680-7324 (Online)

Publisher: Copernicus Publications

Society/Institution: European Geosciences Union (EGU)

LCC Subject Category: Science: Physics | Science: Chemistry

Country of publisher: Germany

Language of fulltext: English

Full-text formats available: PDF, XML

 

AUTHORS

F. Finger (Leipzig Institute for Meteorology (LIM), University of Leipzig, Leipzig, Germany)
F. Werner (Leipzig Institute for Meteorology (LIM), University of Leipzig, Leipzig, Germany)
M. Klingebiel (Institute for Atmospheric Physics, Johannes Gutenberg University Mainz, Mainz, Germany)
A. Ehrlich (Leipzig Institute for Meteorology (LIM), University of Leipzig, Leipzig, Germany)
E. Jäkel (Leipzig Institute for Meteorology (LIM), University of Leipzig, Leipzig, Germany)
M. Voigt (Institute for Atmospheric Physics, Johannes Gutenberg University Mainz, Mainz, Germany)
S. Borrmann (Institute for Atmospheric Physics, Johannes Gutenberg University Mainz, Mainz, Germany)
P. Spichtinger (Institute for Atmospheric Physics, Johannes Gutenberg University Mainz, Mainz, Germany)
M. Wendisch (Leipzig Institute for Meteorology (LIM), University of Leipzig, Leipzig, Germany)

EDITORIAL INFORMATION

Peer review

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Time From Submission to Publication: 16 weeks

 

Abstract | Full Text

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 <i>r</i><sub>eff</sub>, and optical thickness <i>τ</i> 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.