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| Titel |
Observations and Simulations of Three-Dimensional Radiative Interactions between Arctic Boundary Layer Clouds and Ice Floes |
| VerfasserIn |
Michael Schäfer, Eike Bierwirth, André Ehrlich, Evelyn Jäkel, Manfred Wendisch |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250103784
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| Publikation (Nr.) |
 EGU/EGU2015-3201.pdf |
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| Zusammenfassung |
| Based on airborne spectral imaging observations, three-dimensional (3D) radiative effects
between Arctic boundary layer clouds and ice floes have been identified and quantified. A
method is presented to discriminate sea ice and open water in case of clouds from imaging
radiance measurements. This separation simultaneously reveals that in case of clouds the
transition of radiance between open water and sea ice is not instantaneously but horizontally
smoothed. In general, clouds reduce the nadir radiance above bright surfaces in the vicinity of
sea ice - open water boundaries, while the nadir radiance above dark surfaces is enhanced
compared to situations with clouds located above horizontal homogeneous surfaces.
With help of the observations and 3D radiative transfer simulations, this effect was
quantified to range between δLÂ=Â0Âm and δLÂ=Â2200Âm distance to the sea ice
edge. This affected distance δL was found to depend on both, cloud and sea ice
properties. For a ground overlaying cloud in 0200Âm altitude, increasing the cloud
optical thickness from ÏÂ=Â1 to ÏÂ=Â10 decreases δL from 600Âm to 250Âm, while
increasing cloud base altitude or cloud geometrical thickness can increase δL;
δL(ÏÂ=Â1/10)Â=Â2200Âm/1250Âm for 5001000Âm cloud altitude. Furthermore, the
impact of these 3D-radiative effects on retrieval of cloud optical properties was
investigated. The enhanced brightness of a dark pixel next to an ice edge results in
uncertainties of up to 90Â% and 30Â% in retrievals of cloud optical thickness and
effective radius reff, respectively. With help of δL quantified here, an estimate of
the distance to the ice edge for which the retrieval errors are negligible is given. |
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