Lightning – According to the study on the evaluation of atmospheric electric discharges (DEA) in national soil between 2003 and 2017, and to which the Lusa agency had access, the IPMA verified that the “most affected sites are located in the districts of Guarda, Beja, Viseu, Portalegre, Coimbra, Castelo Branco and Vila Real “.
In the district of Guarda “the highest figure was recorded, with DEA 0.358 / km2 / year, followed by the district of Beja with 0.344 DEA / km2 / year,” the document states, in the first case, “the effect caused by Serra da Estrela “as” potentiator of thunderstorm occurrence “.
In the case of Beja, in the Alentejo, the records are based, according to the study, “the development of convective cells (clouds) that can generate thunderstorms”.
With about 940 kilometers of coastline, sea / land contrast is also an “important factor, particularly in the winter when the terrestrial surface, colder than the ocean, promotes the development of convective cells over the sea”, and in the summer, whose heating of the terrestrial surface “propitiates the development of the convective cells in the interior regions”.
And if these favourable conditions for thunderstorm development depend on the state of the atmosphere, in Portugal this occurs essentially in the “passage of more active frontal surfaces, and in the post-frontal cold air, as well as in convective situations (atmospheric instability)”, citing the study as a period of “greater thunderstorm occurrence between May and September, with a peak between 15 and 18 hours.”
The IPMA has based its study on a “network of detectors of atmospheric electrical discharges”, and carry out precise readings since 2003, and that are “constituted by four sensors”, according to the institute.
These reports allow the annual elaboration of “medium density maps of DEA”, where it is possible to “observe the spatial distribution of the thunderstorm in mainland Portugal”, which allowed to update the “average density values for the period 2003-2017, in a regular mesh of 0.2 ° latitude by 0.2 ° longitude, where the DEA considered are cloud-soil type and do not present a location error greater than 10 kilometers, “explained the IPMA.
The study concludes that “Portugal has very low values, below 1.0 DEA / km2 / year,” explained figures “mainly due to the geographic location and time patterns that typically affect the region” .