Influence of heterogeneous freezing on the microphysical and radiative properties of orographic cirrus clouds
The influence of heterogeneous freezing on the microphysical and optical properties of orographic cirrus clouds has been simulated with the large eddy simulation model EULAG. Idealised simulations with different concentrations of ice nuclei (IN) in a dynamically dominated regime with high vertical v...
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2014-07-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/14/6835/2014/acp-14-6835-2014.pdf |
| _version_ | 1818560775944404992 |
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| author | H. Joos P. Spichtinger P. Reutter F. Fusina |
| author_facet | H. Joos P. Spichtinger P. Reutter F. Fusina |
| author_sort | H. Joos |
| collection | DOAJ |
| description | The influence of heterogeneous freezing on the microphysical and optical
properties of orographic cirrus clouds has been simulated with the large eddy
simulation model EULAG. Idealised simulations with different concentrations
of ice nuclei (IN) in a dynamically dominated regime with high vertical
velocities have been performed. Furthermore the temperature at cloud
formation as well as the critical supersaturation for initiation of
heterogenous freezing have been varied. The shortwave, longwave and net
cloud forcing has been calculated under the assumption that the clouds form
between 06:00 and 12:00 local time (LT) or between 12:00 and 18:00 LT. In
general it can be seen that the onset of homogeneous freezing is shifted in
time depending on the IN concentration, as part of the available water vapour
is depleted before the critical threshold for homogeneous freezing is
reached. Although the high vertical velocities in an orographic gravity wave
lead to a strong adiabatic cooling followed by high ice supersaturations, even a
small number concentration of IN of the order of 5 L<sup>−1</sup> is
able to strongly decrease the simulated ice crystal number burden (ICNB), ice
water path (IWP) and optical depth of the cloud. In general,
the ICNB, IWP and optical depth strongly decrease when the IN concentrations
are increased from 0 to 50 L<sup>−1</sup>. The absolute values of the
shortwave, longwave and net cloud forcing are also reduced with increasing IN
concentrations. A cloud will produce a net warming or cooling depending on
the IN concentration, the temperature and the time of day when the cloud
forms. The clouds that form between 06:00 and 12:00 LT are mainly cooling,
whereas the clouds with the same microphysical properties can lead to a
warming when they form between 12:00 and 18:00 LT. In order to predict the
radiative forcing of cirrus clouds it is therefore necessary to take the
correct dynamical and thermodynamical processes as well as the possible
existence and freezing threshold of heterogeneous IN into account, not only
for low vertical velocities but also for dynamically dominated regimes like
orographic cirrus. |
| first_indexed | 2024-12-14T00:42:36Z |
| format | Article |
| id | doaj.art-a2f79a7d4dd04144b459fd3dfd8145f3 |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-12-14T00:42:36Z |
| publishDate | 2014-07-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-a2f79a7d4dd04144b459fd3dfd8145f32022-12-21T23:24:17ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242014-07-0114136835685210.5194/acp-14-6835-2014Influence of heterogeneous freezing on the microphysical and radiative properties of orographic cirrus cloudsH. Joos0P. Spichtinger1P. Reutter2F. Fusina3Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, SwitzerlandInstitute for Atmospheric Physics, Johannes Gutenberg University Mainz, Mainz, GermanyInstitute for Atmospheric Physics, Johannes Gutenberg University Mainz, Mainz, GermanyInstitute for Atmospheric and Climate Science, ETH Zurich, Zurich, SwitzerlandThe influence of heterogeneous freezing on the microphysical and optical properties of orographic cirrus clouds has been simulated with the large eddy simulation model EULAG. Idealised simulations with different concentrations of ice nuclei (IN) in a dynamically dominated regime with high vertical velocities have been performed. Furthermore the temperature at cloud formation as well as the critical supersaturation for initiation of heterogenous freezing have been varied. The shortwave, longwave and net cloud forcing has been calculated under the assumption that the clouds form between 06:00 and 12:00 local time (LT) or between 12:00 and 18:00 LT. In general it can be seen that the onset of homogeneous freezing is shifted in time depending on the IN concentration, as part of the available water vapour is depleted before the critical threshold for homogeneous freezing is reached. Although the high vertical velocities in an orographic gravity wave lead to a strong adiabatic cooling followed by high ice supersaturations, even a small number concentration of IN of the order of 5 L<sup>−1</sup> is able to strongly decrease the simulated ice crystal number burden (ICNB), ice water path (IWP) and optical depth of the cloud. In general, the ICNB, IWP and optical depth strongly decrease when the IN concentrations are increased from 0 to 50 L<sup>−1</sup>. The absolute values of the shortwave, longwave and net cloud forcing are also reduced with increasing IN concentrations. A cloud will produce a net warming or cooling depending on the IN concentration, the temperature and the time of day when the cloud forms. The clouds that form between 06:00 and 12:00 LT are mainly cooling, whereas the clouds with the same microphysical properties can lead to a warming when they form between 12:00 and 18:00 LT. In order to predict the radiative forcing of cirrus clouds it is therefore necessary to take the correct dynamical and thermodynamical processes as well as the possible existence and freezing threshold of heterogeneous IN into account, not only for low vertical velocities but also for dynamically dominated regimes like orographic cirrus.http://www.atmos-chem-phys.net/14/6835/2014/acp-14-6835-2014.pdf |
| spellingShingle | H. Joos P. Spichtinger P. Reutter F. Fusina Influence of heterogeneous freezing on the microphysical and radiative properties of orographic cirrus clouds Atmospheric Chemistry and Physics |
| title | Influence of heterogeneous freezing on the microphysical and radiative properties of orographic cirrus clouds |
| title_full | Influence of heterogeneous freezing on the microphysical and radiative properties of orographic cirrus clouds |
| title_fullStr | Influence of heterogeneous freezing on the microphysical and radiative properties of orographic cirrus clouds |
| title_full_unstemmed | Influence of heterogeneous freezing on the microphysical and radiative properties of orographic cirrus clouds |
| title_short | Influence of heterogeneous freezing on the microphysical and radiative properties of orographic cirrus clouds |
| title_sort | influence of heterogeneous freezing on the microphysical and radiative properties of orographic cirrus clouds |
| url | http://www.atmos-chem-phys.net/14/6835/2014/acp-14-6835-2014.pdf |
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