Atmospheric Chemistry and Physics
www.atmos-chem-phys.net
1680-7316
1680-7324
4
5
2004
10.5194/acp-4-1427-2004
http://www.atmos-chem-phys.net/4/1427/2004/
http://www.atmos-chem-phys.net/4/1427/2004/acp-4-1427-2004.html
http://www.atmos-chem-phys.net/4/1427/2004/acp-4-1427-2004.pdf
1427
1442
2004-08-27
Seasonality and extent of extratropical TST derived from in-situ CO measurements during SPURT
P. Hoor
C. Gurk
D. Brunner
M. I. Hegglin
H. Wernli
H. Fischer
Institute for Atmospheric and Climate Science, Swiss Federal Institute of Technology, Zürich, Switzerland
Max Planck Institute for Chemistry, Air Chemistry, Mainz, Germany
Institute for Atmospheric Physics, University of Mainz, Germany
We present airborne in-situ trace gas measurements which were performed
on eight campaigns between November 2001 and July 2003
during the SPURT-project (SPURenstofftransport in der
Tropopausenregion, trace gas transport in the tropopause region).
The measurements on a quasi regular basis allowed an overview of the seasonal
variations of the trace gas distribution in the tropopause region over
Europe from 35°-75°N to investigate the influence of
transport and mixing across the extratropical tropopause on the
lowermost stratosphere.
<P style="line-height: 20px;">
From the correlation of CO and O<sub>3</sub> irreversible mixing of tropospheric air
into the lowermost stratosphere is identified.
The CO distribution indicates that transport and subsequent mixing of
tropospheric air across the
extratropical tropopause predominantly affects a
layer, which closely follows the shape of the local tropopause.
In addition, the seasonal cycle of CO<sub>2</sub> illustrates the strong coupling
of that layer to the extratropical troposphere.
Both, horizontal gradients of CO on isentropes as well as the
CO-O<sub>3</sub>-distribution in the lowermost stratosphere
reveal that the influence of quasi-horizontal transport and subsequent
mixing weakens with distance from the local tropopause.
The mixing layer extends to about 25 K in potential temperature above
the local tropopause exhibiting only a weak seasonality.
<P style="line-height: 20px;">
However, at large distances from the tropopause a significant influence
of tropospheric air is still evident.
The relation between N<sub>2</sub>O and CO<sub>2</sub> indicates that a
significant contribution of air originating from the tropical tropopause
contributes to the background air in the extratropical lowermost stratosphere.