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| Titel |
Introducing the aerosol-climate model MAECHAM5-SAM2 |
| VerfasserIn |
R. Hommel, C. Timmreck, H. F. Graf |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250025992
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| Zusammenfassung |
| We are presenting a new global aerosol model MAECHAM5-SAM2 to study the aerosol
dynamics in the UTLS under background and volcanic conditions.
The microphysical core modul SAM2 treats the formation, the evolution and the
transport of stratospheric sulphuric acid aerosol. The aerosol size distribution and
the weight percentage of the sulphuric acid solution is calculated dependent on
the concentrations of H2SO4 and H2O, their vapor pressures, the atmospheric
temperature and pressure. The fixed sectional method is used to resolve an aerosol
distribution between 1 nm and 2.6 micron in particle radius. Homogeneous nucleation,
condensation and evaporation, coagulation, water-vapor growth, sedimentation and
sulphur chemistry are included. The module is applied in the middle-atmosphere
MAECHAM5 model, resolving the atmosphere up to 0.01 hPa (~80 km) in 39
layers.
It is shown here that MAECHAM5-SAM2 well represents in-situ measured
size distributions of stratospheric background aerosol in the northern hemisphere
mid-latitudes. Distinct differences can be seen when derived integrated aerosol
parameters (surface area, effective radius) are compared with aerosol climatologies
based on the SAGE II satellite instrument (derived by the University of Oxford and
the NASA AMES laboratory). The bias between the model and the SAGE II data
increases as the moment of the aerosol size distribution decreases. Thus the modeled
effective radius show the strongest bias, followed by the aerosol surface area density.
Correspondingly less biased are the higher moments volume area density and the
mass density of the global stratospheric aerosol coverage. This finding supports the
key finding No. 2 of the SPARC Assessment of Stratospheric Aerosol Properties
(2006), where it was shown that during periods of very low aerosol load in the
stratosphere, the consistency between in-situ and satellite measurements, which exist in a
volcanically perturbed stratosphere, breaks down and significant differences exist between
the systems for key aerosol parameters including the aerosol surface area density. |
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