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Investigating lower stratospheric model transport: Lagrangian calculations of mean age and age spectra in the GCM ECHAM4

Reithmeier, Christian and Sausen, Robert and Grewe, Volker (2008) Investigating lower stratospheric model transport: Lagrangian calculations of mean age and age spectra in the GCM ECHAM4. Climate Dynamics, 30, pp. 225-238. Springer. DOI: 10.1007/s00382-007-0294-1 ISSN 0930-7575


Official URL: http://www.springerlink.com/content/k5x33514wn1607r7/fulltext.pdf


The Lagrangian scheme ATTILA is used to calculate age spectra and the mean age of air in the general circulation model ECHAM4. The advantage of the Lagrangian method is that temporal variation in transport is taken into account and that beyond transport times the actual transport pathways can be investigated. We found a strong seasonal cycle in mean age and age spectra, especially at high latitudes. When plotting polar age spectra against time, it can clearly be seen that the edge of the polar vortex acts as an efficient transport barrier and that exchange with extra-polar air takes place only for a short period of approximately two months after the polar vortex has broken down. Compared to observations the mean age is reproduced satisfactorily below approximately 20 km. Above that level however, the mean age is underestimated, especially at high latitudes. Furthermore, the observed sharp meridional gradient is located too far polewards in the model, which indicates that the subtropical transport barrier is too weak. There is a distinct variation in the shape of the age spectra with latitude. At low latitudes the age spectra consist of one single peak, whereas at higher latitudes secondary peaks appear, which are one year apart and whose positions in the spectrum are independent of the location. At polar latitudes there are even several peaks of approximately equal size. We explain these peaks with two superposing processes. First, the seasonal cycle of the upward mass flux at the tropical tropopause produces a single peak age distribution. And second, at polar latitudes, the temporal evolution of the polar vortex allows mixing of polar and subtropical air only once a year, which results in a superposition of these single peak age distributions. A final investigation of the transport pathways gave indications for predominant routes from the tropics to high latitudes resulting in altitude dependent meridional transport, however, more detailed studies of 3D trajectory data will be needed to clarify this issue.

Item URL in elib:https://elib.dlr.de/49858/
Document Type:Article
Title:Investigating lower stratospheric model transport: Lagrangian calculations of mean age and age spectra in the GCM ECHAM4
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Reithmeier, ChristianDLR, IPAUNSPECIFIED
Date:July 2008
Journal or Publication Title:Climate Dynamics
Refereed publication:Yes
Open Access:Yes
Gold Open Access:No
In ISI Web of Science:Yes
DOI :10.1007/s00382-007-0294-1
Page Range:pp. 225-238
Keywords:Lagrangian transport, global climate modelling, Stratosphere, SF6, age of air
HGF - Research field:Aeronautics, Space and Transport (old)
HGF - Program:Space (old)
HGF - Program Themes:W EO - Erdbeobachtung
DLR - Research area:Space
DLR - Program:W EO - Erdbeobachtung
DLR - Research theme (Project):W - Vorhaben Atmosphären- und Klimaforschung (old)
Location: Oberpfaffenhofen
Institutes and Institutions:Institute of Atmospheric Physics > Atmospheric Dynamics
Deposited By: Grewe, Prof. Dr. Volker
Deposited On:17 Dec 2007
Last Modified:31 Jul 2019 19:20

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