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| Titel |
Comparison of parameterizations for homogeneous and heterogeneous ice nucleation |
| VerfasserIn |
T. Koop, B. Zobrist |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250025361
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| Zusammenfassung |
| The formation of ice particles from liquid aqueous aerosols is of central importance for the
physics and chemistry of high altitude clouds. In this paper, we present new laboratory data
on ice nucleation and compare them with two different parameterizations for homogeneous as
well as heterogeneous ice nucleation. In particular, we discuss and evaluate the effect of
solutes and ice nuclei.
One parameterization is the λ-approach which correlates the depression of the freezing
temperature of aqueous droplets in comparison to pure water droplets, ÎTf, with the
corresponding depression, ÎTm, of the equilibrium ice melting point: ÎTf = λ -
ÎTm.
Here, λ is independent of concentration and a constant that is specific for a particular solute
or solute/ice nucleus combination. The other approach is water-activity-based ice nucleation
theory which describes the effects of solutes on the freezing temperature Tf via their effect
on water activity: aw(Tf) = awi(Tf) + Îaw. Here, awi is the water activity of ice and
Îaw is a constant that depends on the ice nucleus but is independent of the type of
solute.
We present new data on both homogeneous and heterogeneous ice nucleation with
varying types of solutes and ice nuclei. We evaluate and discuss the advantages and
limitations of the two approaches for the prediction of ice nucleation in laboratory
experiments and atmospheric cloud models. |
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