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| Titel |
Improved representation of stratocumulus clouds and the anthropogenic aerosol effect |
| VerfasserIn |
David Neubauer, Ulrike Lohmann, Corinna Hoose, Grazia M. Frontoso |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250093192
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| Publikation (Nr.) |
 EGU/EGU2014-7697.pdf |
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| Zusammenfassung |
| Stratocumulus clouds are important for future climate predictions as they have a strong
cooling effect and the feedback of low clouds is believed to be a major cause of the model
spread in climate sensitivity. Stratocumulus clouds are difficult to represent in a general
circulation model because of their small vertical extent. Stratocumulus regions are also areas
of a strong anthropogenic aerosol effect. Simulations of the anthropogenic aerosol effect can
be expected to depend on the representation of stratocumulus clouds in climate
models.
We address the representation of several of the physical processes that have to
be accounted for when modeling stratocumuli in the general circulation model
ECHAM6 (Stevens et al., 2013) coupled to the aerosol module HAM2 (Zhang et
al., 2012). As a ‘long tail’ stability function can lead to excessive mixing at high
stabilities we replaced it with a ‘sharp’ stability function. The stratocumulus cloud
cover and liquid water path increase, similar to previous studies, with the ‘sharp’
stability function in ECHAM6-HAM2. We also study the impact of increased vertical
resolution in the lower troposphere in ECHAM6-HAM2 on stratocumulus clouds. First
results show improvements for the cloud height and thickness with increased vertical
resolution. To simulate a realistic mixing state and size of particles released by
evaporation of clouds and precipitation we include aerosol processing in stratiform
clouds.
First results from multi-year simulations show that using a ‘sharp’ stability function
decreases the anthropogenic aerosol effect from -1.5 W/m2 to -1.2 W/m2 and in-cloud
aerosol processing to -0.8 W/m2. This strong decrease is due to an increase in the background
aerosol load. Increased vertical resolution doesn’t seem to affect the anthropogenic aerosol
effect in the global average.
Further results on the impact of changing the vertical resolution, a different stability
function and in-cloud aerosol processing in ECHAM6-HAM2 on the anthropogenic aerosol
effect will be presented at the conference.
Stevens et al., 2013, doi: 10.1002/jame.20015
Zhang et al., 2012, doi: 10.5194/acp-12-8911-2012 |
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