Evolution of lightning in eastern Pacific Tropical Cyclones as they approach the coast of Mexico

Lightning activity in tropical cyclones has been the focus of recent research, with some evidence that the intensification is associated with increased lightning activity in the core of the system. Other studies have indicated that an increase in the activity in the outer bands can be related to the inflow of continental cloud condensation nuclei (CCN) as the cyclones approaches land, affecting cloud microphysics and therefore, electrification of the clouds in those bands.

We have analyzed the lightning activity associated with tropical cyclones that developed in the Eastern Pacific basin, off the coast of Mexico, to evaluate the hypothesis that continental CCN affect lightning activity as cyclones approach the coast and right prior to landfall.

The lightning dataset is determined by the World Wide Lightning Location network (WWLLN), that detects the “spherics” associated with lightning, for the period 2005-2011, The official tropical cyclones trajectories, maximum winds and minimum pressures were obtained from the National Hurricane Center. We have considered 9 cyclones whose centers made landfall as well as 7 that we have called “land-grazing”, in which only outer bands made landfall. We have divided the lightning data for each of them into an internal circle with a radius of 111 km and 2 surrounding annuli of 111km and 166km, respectively. It is important to note that most of the tropical cyclones that make landfall originate relatively close to the Mexican coast, so there may be influence of continental CCN even at the earlier stages of development. The preliminary results indicate a relationship between lightning and distance from the coast, slightly increasing.

These results are in the process of being compared with 2 other lightning datasets (STARNET, also measures “spherics” and it is based in Brasil) and the total lightning network (from Earth Networks) to confirm our preliminary results.