 |
| Titel |
The interannual variability of the stratospheric aerosol layer as seen in MAECHAM5-SAM2 |
| VerfasserIn |
R. Hommel, C. Timmreck, M. A. Giorgetta, H. F. Graf |
| Konferenz |
EGU General Assembly 2009
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250026169
|
|
|
|
|
|
| Zusammenfassung |
| In the lower stratosphere the interannual variability of gaseous constituents is dominated by
the quasi-biennial oscillation (QBO). Although the QBO is a phenomenon of the equatorial
stratosphere, the QBO affects the atmospheric dynamics and thus trace gas concentrations in
all latitudes, from the tropical stratospheric reservoir (TSR) to the polar vortex. In tracers
such effects are reflected by concentration gradients and by the formation of characteristic
concentration patterns dependent on the phase of the QBO, the annual cycle, tropopause
exchange processes and chemical pathways. In recent years QBO effects e.g. in CH4 and O3
were studied widely. Little attention was given to QBO modulations in lower stratospheric
particulate matter. However, SAGE and HALOE observations of tropical stratospheric
aerosol extinctions exposed a typical biennial signal that could be linked to the
QBO.
We are presenting the first comprehensive modeling study of QBO effects in the global
stratospheric aerosol layer under non-volcanic conditions, using the size resolved
aerosol-climate model of the middle and upper atmosphere MAECHAM5-SAM2. Our model
studies show that in the vicinity of descending equatorial zonal winds QBO induced
anomalies were found in all prognostic and diagnostic aerosol parameters as well as in
concentrations of sulphate aerosol precursor gases. Qualitatively QBO modulations in the
modeled aerosol mixing ratio correspond to modulations found in space-borne observations
of aerosol extinction. Phase shifts and phase inversions in the modelled aerosol parameter
anomalies are caused by non-linearities in QBO controlled process interactions. QBO
induced anomalies in the aerosol number concentration are a function of particle size.
Enhanced reversible gas-to-particle partitioning (condensation, evaporation) has been
found in regions above the aerosol concentration maximum, which is linked to QBO
modulations in both thermodynamic quantities and advective transport. Observational
findings of the upper and lower transport regimes for stratospheric tracers out of
the TSR are reproduced by the model, while the secondary circulation associated
with the QBO can be identified by the modelled aerosol concentration gradients. |
|
|
|
|
|
|