Is increasing ice crystal sedimentation velocity in geoengineering simulations a good proxy for cirrus cloud seeding?
The complex microphysical details of cirrus seeding with ice nucleating particles (INPs) in numerical simulations are often mimicked by increasing ice crystal sedimentation velocities. So far it has not been tested whether these results are comparable to geoengineering simulations in which cirrus cl...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-04-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/17/4871/2017/acp-17-4871-2017.pdf |
| Summary: | The complex microphysical details of cirrus seeding with ice nucleating
particles (INPs) in numerical simulations are often mimicked by increasing
ice crystal sedimentation velocities. So far it has not been tested whether
these results are comparable to geoengineering simulations in which cirrus
clouds are seeded with INPs. We compare simulations where the ice crystal
sedimentation velocity is increased at temperatures colder than
−35 °C with simulations of cirrus seeding with INPs using the
ECHAM-HAM general circulation model. The radiative flux response of the two
methods shows a similar behaviour in terms of annual and seasonal averages.
Both methods decrease surface temperature but increase precipitation in
response to a decreased atmospheric stability. Moreover, simulations of
seeding with INPs lead to a decrease in liquid clouds, which counteracts part
of the cooling due to changes in cirrus clouds. The liquid cloud response is
largely avoided in a simulation where seeding occurs during night only.
Simulations with increased ice crystal sedimentation velocity, however, lead to counteracting mixed-phase cloud responses. The increased
sedimentation velocity simulations can counteract up to 60 % of the
radiative effect of CO<sub>2</sub> doubling with a maximum net top-of-the-atmosphere forcing of −2. 2 W m<sup>−2</sup>. They induce a 30 % larger surface temperature response, due to their lower altitude of maximum diabatic forcing
compared with simulations of seeding with INPs. |
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| ISSN: | 1680-7316 1680-7324 |