Scientific Results

Contribution of mixing to upward transport across the tropical tropopause layer (TTL)

Year: 2007

Authors: Konopka P., Gunther G., Muller R., dos Santos F.H.S., Schiller C., Ravegnani F., Ulanovsky A., Schlager H., Volk C. M., Viciani S., Pan L.L., McKenna D.-S., Riese M.

Autors Affiliation: Forschungszentrum Julich (ICG-1: Stratosphare), Germany;
CNR-ISAC, Bologna, Italy;
CAO, Dolgoprudny, Russia;
Institut fur Physik der Atmosphare, DLR Oberpfaffenhofen, Germany;
Institut fur Meteorologie und Geophysik, Universitat Frankfurt, Germany;
CNR – Istituto Nazionale di Ottica Applicata, Largo E. Fermi 6, 50125 Firenze, Italy;
National Center for Atmospheric Research, Boulder, CO, USA

Abstract: During the second part of the TROCCINOX campaign that took place in Brazil in early 2005, chemical species were measured on-board the high-altitude research aircraft Geophysica (ozone, water vapor, NO, NOy, CH4 and CO) in the altitude range up to 20 km (or up to 450K potential temperature), i.e. spanning the entire TTL region roughly extending between 350 and 420 K. Here, analysis of transport across the TTL is performed using a new version of the Chemical Lagrangian Model of the Stratosphere (CLaMS). In this new version, the stratospheric model has been extended to the earth surface. Above the tropopause, the isentropic and cross-isentropic advection in CLaMS is driven by meteorological analysis winds and heating/cooling rates derived from a radiation calculation. Below the tropopause, the model smoothly transforms from the isentropic to the hybrid-pressure coordinate and, in this way, takes into account the effect of large-scale convective transport as implemented in the vertical wind of the meteorological analysis. As in previous CLaMS simulations, the irreversible transport, i.e. mixing, is controlled by the local horizontal strain and vertical shear rates.
Stratospheric and tropospheric signatures in the TTL can
be seen both in the observations and in the model. The composition of air above 350K is mainly controlled 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 the outflow regions of the large-scale convection, offers an explanation for the upward transport of trace species from the main convective outflow at around 350K up to the tropical tropopause around 380 K.

Journal/Review:

Volume: 7 (12)      Pages from: 3285  to: 3308

KeyWords: Atmospheric convection; Atmospheric modeling; Stratosphere; Transport process; Tropical meteorology; Tropopause; Vertical mixing, Brazil; South America, Bivalvia; Tropical tropopause layer; Atmospheric transport; CLaMS
DOI: 10.5194/acp-7-3285-2007

Citations: 64
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English