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| Titel |
A Microphysics Guide to Cirrus Clouds |
| VerfasserIn |
Martina Krämer, Christian Rolf, Anna Luebke, Armin Afchine, Nicole Spelten, Anja Costa, Martin Zöger, Jessica Smith, Robert Herman, Bernhard Buchholz, Volker Ebert, Darrel Baumgardner, Stephan Borrmann, Marcus Klingebiel, Linnea Avallone |
| 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 |
250105887
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| Publikation (Nr.) |
 EGU/EGU2015-5489.pdf |
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| Zusammenfassung |
| Cirrus clouds still represent one of the largest uncertainties in the prediction of the Earth’s
climate (IPCC, 2013) since their microphysical and radiative properties remain poorly or only
partially characterized. One major reason is that it is difficult to measure these properties on
fast-flying, high altitude aircraft. Another problem is that aircraft measurements cannot
capture the evolution of the cirrus clouds properties with time. The most common parameters
that are measured in cirrus clouds -besides the meteorological variables- are ice water content
(IWC), number of ice crystals (Nice) and relative humidity (with respect to ice,
RHice), and sometimes vertical velocity. However, it is difficult to deduce on the
history of ice nucleation and development of microphysical properties from these
observations.
Our study aims to provide a guide to cirrus microphysics, which is compiled from an
extensive set of model simulations covering the broad range of atmospheric conditions
for cirrus formation and evolution. The model results are portrayed in the same
parameter space as the field measurements, i.e. in the temperature - IWC parameter
space. From this representation of simulated cirrus, we can relate the formation
mechanism and history to specific combinations of IWC, Nice and RHice inside of
cirrus as a function of temperature. We validate this analysis approach by evaluating
measurements of about 60h in cirrus during fifteen aircraft campaigns conducted in the last
fifteen years over Europe, Australia and Southern and Northern America. It can be
shown that the field observations indeed show the characteristics expected from
the cirrus guide. For example, high/low IWCs are found together with high/low
Nice.
As a result it is now possible to track, to a certain degree, the formation mechanism and
history of the observed cirrus clouds only from the measurement of IWC and RHice.
Important findings from our study are that (i) a substantial part of thick cirrus with high IWC
originates from mixed phase clouds, i.e. via freezing of liquid droplets, while thin cirrus are
mainly formed directly as ice crystals, and (ii) the major fraction of the observed cirrus are
formed by heterogeneous ice nucleation. |
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