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| Titel |
The radiative effect of supercooled liquid and mixed-phase clouds by active satellite remote sensing |
| VerfasserIn |
Kristof Van Tricht, Stef Lhermitte, Tristan L'Ecuyer, Irina V. Gorodetskaya, Nicole P. M. van Lipzig |
| 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 |
250112957
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| Publikation (Nr.) |
 EGU/EGU2015-13147.pdf |
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| Zusammenfassung |
| Supercooled liquid and mixed-phase clouds are important players in the global climate
system with a strong impact on surface energy budgets. Yet, this impact remains a key
uncertainty in climate models, currently limiting the reliability of future climate projections.
Much is unknown about the physical properties of mixed-phase clouds, including
frequency of occurrence of supercooled water, partitioning between ice and liquid,
the sizes and concentrations of cloud droplets, and vertical distribution of liquid
and ice water contents. Ground-based observations of mixed-phase clouds do not
provide extensive spatial information, leaving the large-scale effects of these clouds
unknown.
With the advent of the CloudSat and CALIPSO satellites, this limitation could potentially
be overcome. The CloudSat fluxes and heating rates (FLXHR-LIDAR) product combines
collocated CloudSat, CALIPSO and MODIS observations into vertical profiles of
cloud microphysical properties and shortwave and longwave radiative fluxes. The
combination of radar and lidar is especially useful for the retrieval of radiative
forcing by mixed-phase clouds. We conducted an evaluation study over the Greenland
ice sheet where low-level mixed-phase clouds occur frequently, showing that the
FLXHR-LIDAR product retrieves the radiative fluxes at the surface with high accuracy.
This radiative flux product, constrained by observations, is therefore capable of
retrieving supercooled liquid and mixed-phase cloud forcing at the surface for the first
time on a global scale. Our results show a high occurrence of mixed-phase clouds
globally, with a consequently large impact on the surface energy budget. The highest
probability of clouds containing supercooled liquid water is found in middle and high
latitudes. Cloud radiative forcing strongly depends on microphysical properties of these
clouds: for example, over Greenland optically thin clouds with liquid water path
< 60 g m-2 have the strongest warming impact on the ice sheet surface energy
balance. Our results urge the need for further improving the representation of clouds
in climate models, to enhance the reliability of global future climate projections. |
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