Rare temperature histories and cirrus ice number density in a parcel and a one-dimensional model
A parcel and a one-dimensional model are used to investigate the temperature dependence of ice crystal number density. The number of ice crystals initially formed in a cold cirrus cloud is very sensitive to the nucleation mechanism and the detailed history of cooling rates during nucleation. A possi...
| Main Author: | |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2014-12-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/14/13013/2014/acp-14-13013-2014.pdf |
| _version_ | 1818839262198497280 |
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| author | D. M. Murphy |
| author_facet | D. M. Murphy |
| author_sort | D. M. Murphy |
| collection | DOAJ |
| description | A parcel and a one-dimensional model are used to investigate the temperature
dependence of ice crystal number density. The number of ice crystals
initially formed in a cold cirrus cloud is very sensitive to the nucleation
mechanism and the detailed history of cooling rates during nucleation. A
possible small spread in the homogeneous freezing threshold due to varying
particle composition is identified as a sensitive nucleation parameter. In a
parcel model, the slow growth rate of ice crystals at low temperatures
inherently leads to a strong increase in ice number density at low
temperatures. This temperature dependence is not observed. The model
temperature dependence occurs for a wide range of assumptions and for either
homogeneous or, less strongly, heterogeneous freezing. However, the parcel
model also shows that random temperature fluctuations result in an extremely
wide range of ice number densities. A one-dimensional model is used to show
that the rare temperature trajectories resulting in the lowest number
densities are disproportionately important. Low number density ice crystals
sediment and influence a large volume of air. When such fall streaks are
included, the ice number becomes less sensitive to the details of nucleation
than it is in a parcel model. The one-dimensional simulations have a more
realistic temperature dependence than the parcel mode. The one-dimensional
model also produces layers with vertical dimensions of meters even if the
temperature forcing has a much broader vertical wavelength. Unlike warm
clouds, cirrus clouds are frequently surrounded by supersaturated air.
Sedimentation through supersaturated air increases the importance of any
process that produces small numbers of ice crystals. This paper emphasizes
the relatively rare temperature trajectories that produce the fewest crystals.
Other processes are heterogeneous nucleation, sedimentation from
the very bottom of clouds, annealing of disordered to hexagonal ice, and
entrainment. |
| first_indexed | 2024-12-19T03:51:30Z |
| format | Article |
| id | doaj.art-4805b276587e44c1bc5ffcd8b228521b |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-12-19T03:51:30Z |
| publishDate | 2014-12-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-4805b276587e44c1bc5ffcd8b228521b2022-12-21T20:36:58ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242014-12-011423130131302210.5194/acp-14-13013-2014Rare temperature histories and cirrus ice number density in a parcel and a one-dimensional modelD. M. Murphy0NOAA ESRL Chemical Sciences Division, Boulder, CO, USAA parcel and a one-dimensional model are used to investigate the temperature dependence of ice crystal number density. The number of ice crystals initially formed in a cold cirrus cloud is very sensitive to the nucleation mechanism and the detailed history of cooling rates during nucleation. A possible small spread in the homogeneous freezing threshold due to varying particle composition is identified as a sensitive nucleation parameter. In a parcel model, the slow growth rate of ice crystals at low temperatures inherently leads to a strong increase in ice number density at low temperatures. This temperature dependence is not observed. The model temperature dependence occurs for a wide range of assumptions and for either homogeneous or, less strongly, heterogeneous freezing. However, the parcel model also shows that random temperature fluctuations result in an extremely wide range of ice number densities. A one-dimensional model is used to show that the rare temperature trajectories resulting in the lowest number densities are disproportionately important. Low number density ice crystals sediment and influence a large volume of air. When such fall streaks are included, the ice number becomes less sensitive to the details of nucleation than it is in a parcel model. The one-dimensional simulations have a more realistic temperature dependence than the parcel mode. The one-dimensional model also produces layers with vertical dimensions of meters even if the temperature forcing has a much broader vertical wavelength. Unlike warm clouds, cirrus clouds are frequently surrounded by supersaturated air. Sedimentation through supersaturated air increases the importance of any process that produces small numbers of ice crystals. This paper emphasizes the relatively rare temperature trajectories that produce the fewest crystals. Other processes are heterogeneous nucleation, sedimentation from the very bottom of clouds, annealing of disordered to hexagonal ice, and entrainment.http://www.atmos-chem-phys.net/14/13013/2014/acp-14-13013-2014.pdf |
| spellingShingle | D. M. Murphy Rare temperature histories and cirrus ice number density in a parcel and a one-dimensional model Atmospheric Chemistry and Physics |
| title | Rare temperature histories and cirrus ice number density in a parcel and a one-dimensional model |
| title_full | Rare temperature histories and cirrus ice number density in a parcel and a one-dimensional model |
| title_fullStr | Rare temperature histories and cirrus ice number density in a parcel and a one-dimensional model |
| title_full_unstemmed | Rare temperature histories and cirrus ice number density in a parcel and a one-dimensional model |
| title_short | Rare temperature histories and cirrus ice number density in a parcel and a one-dimensional model |
| title_sort | rare temperature histories and cirrus ice number density in a parcel and a one dimensional model |
| url | http://www.atmos-chem-phys.net/14/13013/2014/acp-14-13013-2014.pdf |
| work_keys_str_mv | AT dmmurphy raretemperaturehistoriesandcirrusicenumberdensityinaparcelandaonedimensionalmodel |