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| Titel |
Ice nucleation sensitivity studies using the detailed microphysical model MAID |
| VerfasserIn |
Martina Krämer, Margit Hildebrandt |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250041207
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| Zusammenfassung |
| The influence of heterogeneous freezing on the ice crystal number of cirrus clouds have been
evaluated by extensive model simulations using the detailed microphysical model MAID
(Bunz et al., 2008). MAID includes heterogeneous as well as homogeneous freezing and, as a
new feature, freezing thresholds for different types of ice nuclei (IN), derived from ice
nucleation experiments at the cloud chamber AIDA.
Cirrus formation scenarios are simulated in the temperature range 180 - 240Â K in 10Â K
steps. For each temperature, six different vertical velocities were assumed, ranging from 1 -
1000Â cm/s. Thus, one scenario contains 42 model runs. A variety of scenarios are simulated
by variing the IN number between 0.001 and 0.2Â cm-3 and using the freezing thresholds of
coated soot and mineral dust. Further, the simulations are performed for constant vertical
velocities uz as well as for uz superimposed with temperature pertubations of 1 and 3Â K,
respectively.
Earlier studies (Gierens, 2003; Kärcher and Lohmann, 2003) concluded that
homogeneous nucleation dominates in regions with updrafts stronger than 20-30Â cms-1. Our
simulations show that heterogeneous ice formation progressively influences the ice crystal
concentrations up to uz = 100Â cm/s, increasing with the IN number and with the
temperature. Lowering the freezing threshold decreases the ice crystal number,
while temperature pertubations increases the ice concentration, but both only for
uz -¤Â 10 cm/s.
In addition to the ice nucleation sensitivity studies, we performed an intercomparison of
MAID with a detailed microphysical model (DLR Oberpfaffenhofen, B. Kärcher) and a
double moment bulk microphysics scheme (ETH Zürich, P. Spichtinger), resulting in a good
agreement between the models.
References:
Bunz, H., Benz, S., Gensch, I., and Krämer, M. (2008): MAID: a model to simulate UT/LS
aerosols and ice clouds, Envir. Res. Lett., 3, doi10.1088/1748-9326/3/3/035001.
Gierens, K. (2003): On the transition between heterogeneous and homogeneous freezing,
Atmos. Chem. Phys. Discuss., 3, 437-446.
Kärcher, B. and Lohmann, U. (2003): A parameterization of cirrus cloud formation:
Heterogeneous freezing, J. Geophys. Res., 108, doi10.1029/2002 JD003220. |
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