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| Titel |
Ice-Ice Collisions: An Ice Multiplication Process in Atmospheric Clouds |
| VerfasserIn |
Vaughan Phillips, Jun-Ichi Yano |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250046799
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| Zusammenfassung |
| Ice in atmospheric clouds undergoes complex physical processes interacting especially with
radiation, leading to serious impacts on global climate. After their primary production,
atmospheric ice crystals multiply extensively by secondary processes. Here, it is
shown that a mostly overlooked process of mechanical break-up of ice particles by
ice-ice collisions contributes to such observed multiplication. A regime for explosive
multiplication is identified in its phase space of ice-multiplication efficiency and
number concentration of ice particles. Many natural mixed-phase clouds, if they
have copious millimetre-sized graupel, fall into this explosive regime. The usual
Hallett-Mossop (H-M) process of ice multiplication is shown to dominate the overall
ice multiplication when active, as it starts sooner, compared to the break-up ice
multiplication process. However, for deep clouds with a cold base temperature where the
usual H-M process is inactive, the ice break-up mechanism should play a critical
role. Supercooled rain, which may freeze to form graupel directly in only a few
minutes, is shown to hasten such ice multiplication by mechanical break-up, with an
ice enhancement ratio exceeding 1 Ã 104 about 20 minutes after small graupel
first appear. The ascent-dependent onset of sub-saturation with respect to liquid
water during explosive ice multiplication is predicted to determine the eventual ice
concentrations.
Reference:
J.-I. Yano, and V. T. J. Phillips, 2010: Ice–Ice Collisions: An Ice Multiplication Process in
Atmospheric Clouds, J. Atmos. Sci., in press. |
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