Atmospheric Chemistry and Physics Discussions
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2009
10.5194/acpd-9-12597-2009
http://www.atmos-chem-phys-discuss.net/9/12597/2009/
http://www.atmos-chem-phys-discuss.net/9/12597/2009/acpd-9-12597-2009.html
http://www.atmos-chem-phys-discuss.net/9/12597/2009/acpd-9-12597-2009.pdf
12597
12614
2009-05-28
Variability of residence time in the Tropical Tropopause Layer during Northern Hemisphere winter
K. Krüger
S. Tegtmeier
M. Rex
Leibniz-Institute for Marine Sciences at Kiel University (IFM-GEOMAR), Kiel, Germany
Environment Canada, Toronto, Canada
Alfred Wegener Institute for Polar and Marine Research, Potsdam, Germany
For the first time the long-term interannual and spatial variability of
residence time (τ) is presented for the TTL between 360 K and 400 K
theta (~14 to 18 km altitude). The analysis is based on a Lagrangian
approach using offline calculated diabatic heating rates as vertical
velocities, covering Northern Hemisphere (NH) winters from 1962–2004.
<br><br>
The residence time varies spatially. τ, analysed for the Lagrangian Cold
Point (LCP), displays a longer duration time of air parcels between LCP and
400 K over the maritime continent (>50 days), as the LCP tropopause has
a minimum over the maritime continent (<370 K theta). Comparing three
theta layers within the TTL reveals the vertical dependence of τ. We
derive a mean duration time of 34 days for 360–380 K (lower TTL), 38 days
for 380–400 K (upper TTL) and 70 days for 360–400 K theta layers for the
1962–2001 period. A case analysis reveals, that τ is positively skewed
for 360–380 K and 380–400 K during La Niña and El Niño Southern
Oscillation (ENSO) neutral years. For these cases, ~60% of air
parcels travel from 360 K to 380 K within 25 days. There is large
interannual variability for τ varying up to ±20% from the
long-term mean, with strongest variability seen in the lower part of the TTL.
The interannual variability is influenced by extratropical and subtropical
wave driving. Statistical analysis reveals a significant anti-correlation
between the residence time and the extratropical and subtropical wave driving
in the lowermost stratosphere.
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