Variability of residence time in the Tropical Tropopause Layer during Northern Hemisphere winter 1Leibniz-Institute for Marine Sciences at Kiel University (IFM-GEOMAR), Kiel, Germany
2Environment Canada, Toronto, Canada
3Alfred Wegener Institute for Polar and Marine Research, Potsdam, Germany
Received: 18 Apr 2009 – Published in Atmos. Chem. Phys. Discuss.: 28 May 2009 Abstract. 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.
Revised: 13 Aug 2009 – Accepted: 03 Sep 2009 – Published: 16 Sep 2009
The residence time τLCP–400 K, 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.
Citation: Krüger, K., Tegtmeier, S., and Rex, M.: Variability of residence time in the Tropical Tropopause Layer during Northern Hemisphere winter, Atmos. Chem. Phys., 9, 6717-6725, doi:10.5194/acp-9-6717-2009, 2009.