Atmos. Chem. Phys. Discuss., 11, 10031-10068, 2011
www.atmos-chem-phys-discuss.net/11/10031/2011/
doi:10.5194/acpd-11-10031-2011
© Author(s) 2011. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
The detection of post-monsoon tropospheric ozone variability over south Asia using IASI data
B. Barret1,2, E. Le Flochmoen1,2, B. Sauvage1,2, E. Pavelin3, M. Matricardi4, and J. P. Cammas1,2
1Laboratoire d'Aérologie/OMP, Université de Toulouse, Toulouse, France
2CNRS/INSU, UMR 5560, 14 avenue E. Belin, 31400 Toulouse, France
3Met Office, FitzRoy Road, Exeter, Devon, EX1 3PB, UK
4ECMWF, Shinfield Park, Reading, RG2 9AX, UK

Abstract. The ozone (O3) variability over south Asia during the 2008 post-monsoon season has been assessed using measurements from the MetOP-A/IASI instrument and O3 profiles retrieved with the SOftware for a Fast Retrieval of IASI Data (SOFRID). The information content study and error analyses carried out in this paper show that IASI Level 1 data can be used to retrieve tropospheric O3 columns (surface-225 hPa) and UTLS columns (225–70 hPa) with errors smaller than 20%. Validation with global radiosonde O3 profiles obtained during a period of 6 months show the excellent agreement between IASI and radiosonde for the UTLS with correlation coefficient R > 0.91 and good agreement in the troposphere with correlation coefficient R > 0.74. For both the UTLS and the troposphere Relative Standard Deviations (RSD) are lower than 23%. The temporal variability of the vertical profile of O3 has first been observed locally near Hyderabad in central India with in situ measurements from the MOZAIC program. These measurements obtained from airborne instruments show that tropospheric O3 is steadily elevated during most of the studied period with the exception of two sharp drops following the crossing of tropical storms over India. Lagrangian simulations with the FLEXPART model indicate that elevated O3 concentrations in the middle troposphere near Hyderabad are associated with the transport of UT air-masses that have followed the Subtropical Westerly Jet (SWJ) and subsided over northern India together with boundary layer polluted air-masses transported from the Indo-gangetic plain by the north-easterly trades. Low O3 concentrations result from the uplift and westward transport of pristine air-masses from the marine boundary layer of the Bay of Bengal by tropical storms. In order to extend the analysis of tropospheric O3 variability to the whole of south Asia, we have used IASI-SOFRID O3 data. We show that IASI O3 data around Hyderabad were able to capture the fast variability revealed by MOZAIC. Furthermore, their spatio-temporal coverage demonstrates that the behaviour of tropospheric O3 observed near Hyderabad extended over most of central and south India and part of the Bay of Bengal. This result highlights the ability of the IASI sensor to capture fast changes in chemical composition related to dramatic tropical weather conditions.

Citation: Barret, B., Le Flochmoen, E., Sauvage, B., Pavelin, E., Matricardi, M., and Cammas, J. P.: The detection of post-monsoon tropospheric ozone variability over south Asia using IASI data, Atmos. Chem. Phys. Discuss., 11, 10031-10068, doi:10.5194/acpd-11-10031-2011, 2011.
 
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