Cloud to ground flashes in Mexico and adjacent oceanic area: a preliminary study using data from the WWLL network

Data from 2 years (2004 and 2005) of observations of spherics associated with cloud-to-ground discharges were analyzed to determine the spatial patterns in the cloud-to-ground flashes associated with different cloud systems. The measurements are part of the World Wid Lightning Location global spherics network, based on Time of Group Arrival information (http://webflash.ess.washington.edu). Climatologically, the rainy season in the area lasts from May to November, with also the presence of tropical cyclones on all adjacent oceanic areas. The oceanic areas were divided into 4 sub-areas, one in the Caribbean, one in the Gulf of Mexico and two regions in the Pacific (North and South of 20 0N). The meteorological phenomena observed in each of the regions are slightly different. The NW Pacific region is seldom affected by the presence of tropical cyclones, although some of the precipitation is associated with the “monsoon of North America”. The East Pacific region is heavily affected by the Intertropical convergence zone (ITCZ). Tropical cyclones influence both the Caribbean and Gulf of Mexico regions, as well as the East Pacific region.

As expected, the largest fraction of cloud-to-ground flashes is observed over the continental regions. Nevertheless, a very interesting monthly variability is observed in the different oceanic sub-regions. The results showed a different behavior in each region, with the largest number of flashes observed in the Caribbean and the lowest in the NW Pacific region. The latter is the only region that exhibits a single peak in the frequency distribution in the month August for both years. In contrast, the other three regions present a bimodal distribution of flashes in time, with the main peak in August-September and a secondary maximum in May-June. This pattern is shifted earlier in time, during 2005 which was an anomalously active tropical cyclone season in the Atlantic basin. These results will be correlated with the easterly waves and tropical cyclones observed in each region, to determine links between the cyclone development and electrical activity in them.