A first study of the lightning activity related to tropical cyclones in the south-west Indian Ocean

These last years, the interest for the lightning activity of storms has increased with a large panel of scientific applications. Actually, lightning flashes are now recognized as a major source of nitrogen oxides, a precursor of ozone, in the middle and upper troposphere. Some attempts to use lightning data as a proxy for latent heating release for assimilation purpose have also been made. Lightning data can also be used to infer characteristics of thunderstorms. For example, in regions where radar and satellite coverage is sparse, detection of lightning is an appealing way to gain more information on the storm characteristics (intensity, ice mass content...).

The south-west Indian Ocean (30-90°E, 0-40°S) accounts for 10-12% of the global annual activity of tropical storms and tropical cyclones, with an average number of 10.5 tropical storms among which 4.5 become tropical cyclones. However, the satellite and radar coverage in this basin is sparse. The World Wide Lightning Location Network (WWLLN; http://wwlln.net/) that provides real-time lightning location over the entire Earth by measuring the time of group arrival of very low frequency radiation, allows the detection of lightning flashes several thousand kilometers from the source. The data from the WWLLN are then well suited to study the electrical activity all along the lifetime of tropical disturbances in the south-west Indian Ocean for the present cyclone season (November 2009 to April 2010). The objective of this study is to investigate the possible relation between the changes in electrical activity of convective systems to their variations of intensity. Several questions will be addressed: what are the cyclone regions lightning flashes are preferentially associated to? Can variations in cyclone intensity be identified through changes in the lightning activity?