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| Titel |
A permanent aerosol layer at the tropical tropopause layer driven by the intertropical convergence zone |
| VerfasserIn |
Q. Bourgeois, I. Bey, P. Stier |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250065195
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| Zusammenfassung |
| We use observations from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP)
satellite instrument and a global aerosol-climate model to document an aerosol layer that
forms in the vicinity of the tropical tropopause layer (TTL) over the southern Asian and
Indian Ocean region. CALIOP observations suggest that the aerosol layer is present
throughout the year and follows the migration of the Intertropical Convergence Zone (ITCZ).
The layer is located at about 20°N during boreal summers and at about 15°S in
boreal winters. The ECHAM5.5-HAM2 aerosol-climate model reproduces such an
aerosol layer close to the TTL but overestimates the observed aerosol extinction.
The mismatch between observed and simulated aerosol extinctions are discussed
in terms of uncertainties related to CALIOP and possible problems in the model.
Sensitivity model simulations indicate that i) sulfate particles resulting from SO2 and
DMS oxidation are the main contributors to the mean aerosol extinction in the layer
throughout the year, and ii) transport of sulfate precursors by convection followed by
nucleation is responsible for the formation of the aerosol layer. The reflection of
shortwave radiations by aerosols in the TTL may be negligible, however, cloud droplets
formed by these aerosols may reflect about 6 W.m-2 back to space. Overall, this study
provides new insights in term of composition of the tropical upper troposphere. |
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