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| Titel |
Progress in Representing Microphysical Processes in a Snow Growth Model |
| VerfasserIn |
Ehsan Erfani, David Mitchell |
| 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 |
250108534
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| Publikation (Nr.) |
 EGU/EGU2015-8290.pdf |
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| Zusammenfassung |
| A steady-state snow growth model (SGM) has been developed based on the microphysical
growth processes of vapor deposition, aggregation and riming. Climate models use
mass-dimension (m-D) and area-dimension (A-D) power laws (e.g. m = αDβ) to formulate
ice particle growth rates, however it is well known that the m-D and A-D power laws for the
smallest ice particles differ considerably from the power laws for the largest particles. To
overcome this problem, β and α are predicted as a function of diameter where the m-D
expression is a 2nd-order polynomial in log-log space. By tailoring these m-D and A-D
relationships to the SGM, ice particle growth rates and fall speeds are represented
more accurately and realistically. The predicted size spectra by SGM are in good
agreement with observed spectra from Colorado Airborne Mixed-Phase Cloud Study
(CAMPS).
Although ice particle riming often has little impact on ice particle size, its impact on ice
particle mass and projected area can be considerable. A method is introduced to calculate
rimed mass and area from unrimed mass and area, and from maximum mass and area that can
be achieved by riming. The treatment for riming is explicit, accounting for the dependence of
collision efficiency on droplet and ice particle size using both hydrodynamic theory and
experimental measurements. It appears that the riming process is essential in characterizing
the snowfall rates. Moreover, increase in cloud condensation nuclei (CCN), due to
aerosols, can modify cloud droplet SD (size distribution) and therefore decrease the
snowfall rate. So, snowfall rate is sensitive to the shape of cloud droplet SD. It is
speculated that by implementing the new m-D and A-D treatment, and riming growth
in any climate model, the ice particle growth rates will become more accurate. |
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