An upper tropospheric ‘ozone river’ from Africa to India during the 2008 Asian post-monsoon season

Abstract

We have used ozone data from the Infrared Atmospheric Sounding Interferometer to follow an event of ozone-enriched air-masses in the upper troposphere from eastern Africa to northern India. The ozone transport (hereafter called ‘ozone river’ or O3R) occurred during the Asian post-monsoon season in 2008 and was associated with Rossby wave propagation. The persistence of the O3R in a narrow channel was confirmed by MOZAIC airborne data over the northwestern Indian coast. The regions of origin of the O3R were identified by a transport analysis based on the Lagrangian model FLEXPART. The Lagrangian simulations combined with potential vorticity fields indicate that stratospheric intrusions are not likely to be the most important contributor to the observed O₃ enhancements. A high-resolution Eulerian model, Meso-NH, with tagged tracers was used to discriminate between African biomass burning, lightnings and Indian anthropogenic pollution as potential sources of precursors for the O3R. Lightning NOx emissions, associated with convective clouds over Africa, were found to be the principal contributor to the ozone enhancement over the Indian Ocean taking advantage of a northeastward jet. This case study illustrates African lightning emissions as an important source for enhanced O₃ in the upper troposphere over the Indian Ocean region during the post-monsoon season.

• ozone
• Indian Ocean
• upper troposphere
• lightning

7. Acknowledgements

This subject was part of the Flore TOCQUER's PhD thesis, cofinanced by CNES and Météo–France. IASI, developed and built under the responsibility of the Center National d'Etudes Spatiales (CNES, France), is flown onboard the MetOp satellites as part of the EUMETSAT Polar System. IASI L1c and L2–EUMETSAT data have been downloaded from the Ether French atmospheric database (http://ether.ipsl.jussieu.fr). The research concerning IASI is conducted with the financial support of CNES (TOSCA–IASI project). MOZAIC is presently funded by INSU–CNRS, Météo–France, and FZJ (Forschungszentrum Julich, Germany). Interpolated OLR data are provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from their website at http://www.cdc.noaa.gov. Meso-NH model jointly developed by the Laboratoire d'Aérologie (UMR 5560 UPS/CNRS) and by CNRM–GAME (URA 1357 CNRS/Météo–France). Computer time has been provided by the scientific group Calculation in Midi-Pyrenees [CALMIP (grant P12171)].