ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-7-13989-2007 Long-term climatology of air mass transport through the Tropical Tropopause Layer (TTL) during NH winter Krüger K. 1 3 Tegtmeier S. 2 3 Rex M. 3 IFM-GEOMAR, Kiel, Germany University of Toronto, Toronto, Canada Alfred Wegener Institute for Polar and Marine Research, Potsdam, Germany 28 09 2007 7 5 13989 14010 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys-discuss.net/7/13989/2007/acpd-7-13989-2007.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/7/13989/2007/acpd-7-13989-2007.pdf

A long-term climatology of air mass transport through the tropical tropopause layer (TTL) is presented, covering the period from 1962–2005. The transport through the TTL is calculated with a Lagrangian approach using radiative heating rates as vertical velocities in an isentropic trajectory model. We demonstrate the improved performance of such an approach compared to previous studies using vertical winds from meteorological analyses. Within the TTL, the averaged diabatic ascent is 0.5 K/day during Northern Hemisphere (NH) winters 1992–2001, close to observations from the tape recorder. Climatological maps show a cooling and strengthening of this part of the residual circulation during the late 1990s and early 2000s compared to the long-term mean. Lagrangian cold point (LCP) fields show systematic differences for varying time periods and natural forcing components. The interannual variability of LCP temperature and density fields are found to be influenced by volcanic eruptions, ENSO, QBO and the solar cycle. The coldest and driest TTL is reached during QBOE and La Niña over the western Pacific, whereas during volcanic eruptions, El Niño and QBOW it is warmer and less dry.

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