ACP Atmospheric Chemistry and Physics ACP Atmos. Chem. Phys. 1680-7324 Copernicus Publications Göttingen, Germany 10.5194/acp-8-813-2008 Long-term climatology of air mass transport through the Tropical Tropopause Layer (TTL) during NH winter Krüger K. 1 2 Tegtmeier S. 1 3 Rex M. 1 Alfred Wegener Institute for Polar and Marine Research, Potsdam, Germany now at: IFM-GEOMAR, Kiel, Germany now at: University of Toronto, Toronto, Canada 19 02 2008 8 4 813 823 Copyright: © 2008 K. Krüger et al. 2008 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://acp.copernicus.org/articles/8/813/2008/acp-8-813-2008.html The full text article is available as a PDF file from https://acp.copernicus.org/articles/8/813/2008/acp-8-813-2008.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 upper part of the TTL, the averaged diabatic ascent is 0.5 K/day during Northern Hemisphere (NH) winters 1992–2001. Climatological maps show a cooling and strengthening of this part of the residual circulation during the 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 is found to be influenced by volcanic eruptions, El Niño Southern Oscillation (ENSO), Quasi-Biennial Oscillation (QBO) and the solar cycle. The coldest and driest TTL is reached during QBO easterly phase and La Niña over the western Pacific, whereas during volcanic eruptions, El Niño and QBO westerly phase it is warmer and less dry.

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