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| Titel |
Remote sensing of Arctic boundary layer clouds above snow surfaces |
| VerfasserIn |
André Ehrlich, Eike Bierwirth, 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 |
250105711
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| Publikation (Nr.) |
 EGU/EGU2015-5249.pdf |
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| Zusammenfassung |
| In the Arctic remote sensing of clouds using reflected solar radiation is mostly related to high
uncertainties as the contrast between the bright sea ice and snow surface and the clouds is
low. Additionally, uncertainties result from variation of the snow grain size which changes the
absorption of solar radiation similarly to the size of cloud particles. This is a major
issue for understanding the response of Arctic clouds to climate warming as the
quantification of cloud properties in this remote region mostly relies on satellite
observations.
We used spectral radiation measurements of the Spectral Modular Airborne Radiation
measurement sysTem (SMART-Albedometer) to improve common used cloud remote sensing
algorithms in case of snow surfaces. The measurements were collected during the airborne
research campaign Vertical distribution of ice in Arctic mixed-phase clouds (VERDI,
April/May 2012) above the Canadian Beaufort where both sea ice covered and ice free ocean
areas were present during the observation period. Based on the spectral absorption
characteristics of snow and clouds (assuming to be dominated by the liquid fraction) a
combination of wavelengths was found which allows to separate the impact of
clouds and snow surface on the reflected radiation measured above the clouds. While
snow grain size dominates the absorption at a wavelength of 1.0 μm, information
on cloud optical thickness and cloud particle effective radius can be extracted at
wavelengths of 1.7 μm and 2.1 μm, respectively. Based on radiative transfer simulations
lookup tables for the retrieval algorithm were calculated and used to estimate the
theoretical uncertainties of the retrieval. It was found that using ratios instead of absolute
radiances reduces the uncertainties significantly. The new algorithm was applied to a
specific case observed during the VERDI campaign where a stratocumulus clouds was
located above an ice edge. It could be shown that the method works also over water
surfaces and provides similar cloud optical properties above ice covered and ice free
surfaces. In addition the snow grain size could be derived also in cloud covered
areas. |
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