P3.14
Transport processes in the tropical tropopause layer (TTL) -- Observations versus multi-annual simulations with CLaMS
Paul Konopka, Forschungszentrum Jülich, Jülich, Germany; and G. Günther, J. -. U. Grooß, R. Müller, C. Schiller, A. Ulanovsky, C. M. Volk, S. Viciani, and L. Pan
The composition of the air entering the stratosphere is mainly determined by the transport processes within the tropical tropopause layer (TTL) coupling the Hadley circulation in the tropical troposphere with the much slower, Brewer-Dobson circulation in the stratosphere.
During recent tropical campaigns that took place in Brazil (Troccinox 2005), Australia (Scout 2005) and Africa (Amma 2006), chemical species were measured on-board of the high flying research aircraft Geophysica (ozone, N2O, CH4, CO2, CO, water vapor) in the altitude range up to 20 km (or up to 450 K pot. Temp), i.e.~well-covering the TTL region roughly extending between 350 and 420 K. This unique data set, together with the multi-annual (2001-2006) model simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS) allows to check our understanding of the dynamical processes occurring in the TTL.
In addition to the convection and radiation-dominated parts of transport, the composition of air above ~350 K is strongly influenced by mixing on a time scale of weeks or even months. Based on CLaMS transport studies where mixing can be completely switched off, we deduce that vertical mixing, mainly driven by the vertical shear in the tropical flanks of the subtropical jets and, to some extent, in the outflow regions of the large-scale convection offers an explanation for the upward transport from the main convective outflow around 350 K up to the tropical tropopause around 380 K. Thus, the seasonal dependence of the composition of the TTL is controlled by the permeability of the subtropical jets with a strong influence of the Asian monsoon during the boreal summer. We discuss the impact of these effects on the formation of the stratospheric tape-recorder.
Poster Session 3, Recent Field Investigations of TTL
Tuesday, 21 August 2007, 1:30 PM-3:30 PM, Holladay
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