Resumen de Análisis de la actividad de rayos y de tormentas relacionadas con la producción de rayos gamma terrestres
Ferran Fabró Tapia
Terrestrial Gamma ray Flashes (TGFs) have been known since 20 years ago, but since the first moment of the discovery it was clear that they were related to lightning and thunderstorms. The latest studies revealed that TGFs could be produced during the first stages of the lightning within thunderclouds by a process which is very similar to the X-ray emissions from natural lightning observed from ground or discharges in high voltage laboratory. The study of such phenomena will help to extend and complete the knowledge about lightning and electrical discharges. This study compares geographic, monthly and diurnal cycle global distributions of TGFs and lightning. A fourth region with enhanced production of TGFs has been identified apart from the other three regions previously identified. This analysis further investigates the relation between TGFs, lightning activity and thunderstorms. Moreover, we have seen that the TGF/lightning ratio is different in each region which could be explained by meteorological differences between regions and not by differences in regional lightning detection efficiency. For the first time, meteorological conditions and lightning activity have been compared among situations where a satellite with capability to detect TGFs did or did not detect them. The objective is to identify the best atmospheric conditions for TGF production. We have established that electrification processes associated with strong updrafts and high CAPE values are important to create the best atmospheric conditions that favours TGF generation. In the second part of the study we defined criteria for the TGF/lightning correlation in time. Using these criteria we have identified 90 correlations in South America. Depending on the time difference between TGF and lightning the correlations have been grouped into different categories. For each category the relation between TGF and lightning was justified based on examples of upward propagation of negative leaders detected by a VHF lightning mapping network, consistent with the currently most accepted production theories. We were able to identify associated thunderstorms in 32 of 90 correlation cases. We have analysed the thunderstorm development stage at the moment of TGF production, the vertical extent and areal extent. It was found that analysed thunderstorms shows preferences for TGF production during developing or mature stages and great vertical extension what agrees with situations with strong updrafts and high CAPE values determined in the first part of the study. The last part presents an analysis of the association between X-ray events and lightning registered at the Eagle Nest Tower in the Pyrenees. We have determined that downward negative lightning seems to be the only candidate for x-ray emissions. The theories that support this hypothesis could also explain TGF production, specifically, as in examples of upward negative leaders shown in the previous section. We have also studied whether the high energy background radiation increased in association with thunderstorm electrification. However, in the cases analysed this increase has been associated with radon-ion daughters.
