Long-term climatology of air mass transport through the Tropical Tropopause Layer (TTL) during NH winter K. Krüger1,*, S. Tegtmeier1,**, and M. Rex1 1Alfred Wegener Institute for Polar and Marine Research, Potsdam, Germany *now at: IFM-GEOMAR, Kiel, Germany **now at: University of Toronto, Toronto, Canada
Abstract. 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.
Citation: Krüger, K., Tegtmeier, S., and Rex, M.: Long-term climatology of air mass transport through the Tropical Tropopause Layer (TTL) during NH winter, Atmos. Chem. Phys., 8, 813-823, doi:10.5194/acp-8-813-2008, 2008.