Index Geophysics

Variability of residence time in the Tropical Tropopause Layer during Northern Hemisphere winter

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 &tau;_{LCP&ndash;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 (&gt;50 days) over the maritime continent as the LCP is lowest there (&lt;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 &plusmn;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.

Krüger, K.

Tegtmeier, S.

Rex, M.

2018-01-15

info:eu-repo/semantics/Text

info:eu-repo/semantics/application/pdf

10.5194/acp-9-6717-2009

https://acp.copernicus.org/articles/9/6717/2009/

eISSN: 1680-7324

eng

info:eu-repo/grantAgreement/EC/FP7/226224

info:eu-repo/semantics/openAccess