Diagnostics of the tropical tropopause layer from in-situ observations and CCM data

Year: 2009

Authors: Palazzi E., Fierli F., Cairo F., Cagnazzo C., Di Donfrancesco G., Manzini E., Ravegnani F., Schiller C., D’Amato F., Volk C.M.

Autors Affiliation: ISAC-Institute for Atmospheric Sciences and Climate, National Research Council, Italy
CMCC-Centro Euro-Mediterraneo per i Cambiamenti Climatici, Italy
ENEA-Ente Nuove Tecnologie Energia e Ambiente, Rome, Italy
INGV-Istituto Nazionale di Geofisica e Vulcanologia, Italy
FZJ, Forschungzentrum Julich, GMBH, Germany
INOA-CNR, Istituto Nazionale di Ottica Applicata, Italy
J. W. Goethe University, Frankfurt, Germany

Abstract: A suite of diagnostics is applied to in-situ aircraft measurements and one Chemistry-Climate Model (CCM) data to characterize the vertical structure of the Tropical
Tropopause Layer (TTL). The diagnostics are based on vertical tracer profiles and relative vertical tracer gradients, using tropopause-referenced coordinates, and tracer-tracer relationships in the tropical Upper Troposphere/Lower Stratosphere (UT/LS). Observations were obtained during four tropical campaigns performed from 1999 to 2006 with the research aircraft Geophysica and have been compared to the output of the ECHAM5/MESSy CCM. The model vertical resolution in the TTL (~500 m) allows for appropriate comparison with
high-resolution aircraft observations and the diagnostics used highlight common TTL features between the model and the observational data. The analysis of the vertical profiles of water vapour, ozone, and nitrous oxide, in both the observations and the model, shows that concentration mixing ratios exhibit a strong gradient change across the tropical tropopause, due to the role of this latter as a transport barrier and that transition between the tropospheric and stratospheric regimes occurs within a finite layer. The use of relative vertical ozone and carbon monoxide gradients, in addition to the vertical profiles, helps to highlight the region where this transition occurs and allows to give an estimate of its thickness. The analysis of the CO-O3 and H2O-O3 scatter plots and of the Probability Distribution Function (PDF) of the H2O-O3 pair completes this picture as it allows to better distinguish tropospheric and stratospheric regimes that can be identified by their different chemical composition. The joint analysis and comparison of observed and modelled
data allows to state that the model can represent the
background TTL structure and its seasonal variability rather
accurately. The model estimate of the thickness of the interface region between tropospheric and stratospheric regimes agrees well with average values inferred from observations.
On the other hand, the measurements can be influenced by
regional scale variability, local transport processes as well as deep convection, that can not be captured by the model.

Journal/Review:

Volume: 9 (24)      Pages from: 9349  to: 9367

More Information: Authors acknowledge the partial support of the EC SCOUT-O3 Integrated Project (505390- GOCE-CT-2004). Chiara Cagnazzo and Elisa Manzini acknowledge the partial support of Centro Euro-Mediterraneo per i Cambiamenti Climatici. The model simulation were performed at ECMWF, under the Special Project on Middle Atmosphere Modelling.
KeyWords: Accuracy assessment; Airborne survey; Aircraft; Atmospheric chemistry; Carbon monoxide; Chemical composition; Climate modeling; Concentration (composition); In situ measurement; Mixing ratio; Nitrous oxide; Observational method; Ozone; Probability density function; Research work; Seasonal variation; Stratosphere; Tracer; Tropical meteorology; Tropopause; Troposphere; Vertical profile; Water vapor
DOI: 10.5194/acp-9-9349-2009

Citations: 6
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