Atmospheric Chemistry and Physics
www.atmos-chem-phys.net
1680-7316
1680-7324
9
18
2009
10.5194/acp-9-6717-2009
http://www.atmos-chem-phys.net/9/6717/2009/
http://www.atmos-chem-phys.net/9/6717/2009/acp-9-6717-2009.html
http://www.atmos-chem-phys.net/9/6717/2009/acp-9-6717-2009.pdf
6717
6725
2009-09-16
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
potential temperature (~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 τ<sub>LCP–400 K</sub>, being the duration time of air parcels in
the layer between the Lagrangian Cold Point (LCP) and 400 K, varies
spatially and is longer (>50 days) over the maritime continent as the LCP
is lowest there (<370 K). 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. 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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