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| Titel |
Using the Convective Cloud Field Model (CCFM) to investigate aerosol-convection interactions in ECHAM6-HAM |
| VerfasserIn |
Zak Kipling, Philip Stier, Till Wagner |
| 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 |
250097310
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| Publikation (Nr.) |
 EGU/EGU2014-12875.pdf |
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| Zusammenfassung |
| Convection plays an important role in the climate system through its effects on radiation,
precipitation, large-scale dynamics and vertical transport of aerosols and trace gases. The
effects of aerosols on the development of convective cloud and precipitation are a source of
considerable uncertainty in current climate modelling.
Most current global climate models use “mass-flux” convection schemes, which represent
the ensemble of convective clouds in a GCM column by a single “mean” updraught. In
addition to over-simplifying the representation of such clouds, this presents particular
problems in the context of aerosol–convection interactions: firstly because the relationship
between aerosol and the droplet size distribution depends on the vertical velocity
distribution, about which little or no information is available, and secondly because
the effects of convective transport and scavenging may vary nonlinearly over the
ensemble (e.g.between precipitating and non-precipitating clouds and due to different
loadings).
The Convective Cloud Field Model (CCFM) addresses these limitations by simulating
a spectrum of updraughts with different cross-sectional areas within each GCM
column, based on the quasi-equilibrium approach of Arakawa and Schubert. For each
cloud type, an entraining Lagrangian parcel model is initiated by perturbations at
the surface, allowing a realistic vertical velocity to develop by cloud base so that
detailed size-resolved microphysics can be represented within the cloud above. These
different cloud types interact via competition for resolved-scale convective available
potential energy (CAPE). Transport of water, aerosol and other tracers is calculated
separately for each cloud type, allowing for different entrainment and scavenging
behaviours.
By using CCFM embedded within the ECHAM6–HAM aerosol–climate model, we show
how this approach can both improve the distribution of convective precipitation events
compared to a typical mass-flux scheme, and also enable the physically-based representation
of aerosol indirect effects to be extended to include sub-grid-scale convective cloud and
precipitation. |
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