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| Titel |
Cirrus clouds as seen by the CALIPSO satellite and ECHAM-HAM global climate model |
| VerfasserIn |
Blaz Gasparini, Angela Meyer, David Neubauer, Steffen Münch, Ulrike Lohmann |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250143384
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| Publikation (Nr.) |
 EGU/EGU2017-7096.pdf |
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| Zusammenfassung |
| Ice clouds impact the planetary energy balance and upper tropospheric water vapour
transport and are therefore relevant for climate. In this study ice clouds at temperatures
below -40∘C simulated by the ECHAM-HAM global climate model are compared to
CALIPSO/CALIOP satellite data. The model reproduces well the mean occurrence of ice
clouds, while the ice water path, ice crystal radius, cloud optical depth and extinction
are overestimated in terms of annual means and temperature dependent frequency
histograms. Two distinct types of cirrus clouds are found: in-situ formed cirrus
dominating at temperatures below -60∘C and liquid-origin cirrus, dominating at
temperatures warmer than -55∘C. The latter form in anvils of deep convective clouds or by
glaciation of mixed-phase clouds. They are associated with ice water contents of up
to 0.1 g m−3 and extinctions of up to 0.1 km−1, while the in-situ formed cirrus
are optically thinner and contain at least an order of magnitude less ice. The ice
cloud properties do not differ significantly between the southern and the northern
hemisphere.
In-situ formed ice clouds are further divided into homogeneously and heterogeneously
nucleated ones. The simulated liquid-origin ice crystals mainly form in convective outflow in
large number concentrations, similar to in-situ homogeneously nucleated ice crystals. On the
contrary, heterogeneously nucleated ice crystals are associated with smaller number
concentrations. However, ice crystal aggregation and depositional growth smooth the
differences between several formation mechanisms making the attribution to a specific ice
nucleation mechanism challenging. |
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