The UPC Lightning Research Group was founded in 2001 to study lightning strikes and their effects. In 2005 the European Union research network “Coupling of Atmospheric Layers” attracted the group's interest to mesospheric streamer and glow phenomena related to lightning: red sprites, elves, blue jets and gigantic jets (in short TLE). In the last 10 years, strong emissions from lightning to space known as terrestrial gamma-ray flashes (TGF) received increasing attention. Hundreds of sprites and elves are commonly observed in southwestern Europe each year, but TGFs and gigantic jets (GJs) which directly connect the cloud with the ionosphere are mainly found in the tropics where thunderstorm cloud tops can reach higher.
In 2005, we started our work in the Eagle Nest Tower. It is not a tall tower but it is located in a mountain peak, where conditions are prone to upward lightning, initiated by the tower itself. In it, we can measure both direct and indirect lightning effects. With the aim to study high energy emissions produced by lightning, a new equipment was installed during summer 2011. The equipment is composed by a high speed camera, two NaI(Tl) scintillation detectors, a ‘fast’ E-Field antenna and a VHF antenna. The instrument is located at few meters of the tower base. The Eagle Nest tower area is well covered by the XDDE VHF interferometer system by the Meteorological Service of Catalonia and the VLF/FL network LINET. Moreover, after October 2011 a three-dimensional stand-alone VHF interferometer was installed at a few kilometers of the tower. The area of interest is also well covered by four C-band volumetric meteorological radar.
Since 2008 the UPC group was involved in three projects of the Spanish cooperation in the Atmosphere-Space Interactions Monitor (ASIM) mission of the European Space Agency (ESA). The group acquired detectors for energetic radiation from lightning and a fast camera to optically resolve fast processes in lightning and sprites, revealing complex streamer interactions in sprites for the first time in Europe. The Ebro Valley Laboratory (EVL) was established as the most complete facility in Europe for natural lightning studies. The key is a Lightning Mapping Array (LMA) of 12 VHF radio receivers, which reveal 3D lightning channel developments inside the cloud over a range around the Ebro Delta. It is supplemented by other lightning locating networks and the Eagle Nest tower. The Eagle Nest tower has been instrumented in order to measure lightning currents and high energy radiation. X-rays from lightning has been studied in the Eagle Nest tower. The group conducted experiments in the high voltage laboratory producing X-rays form 1 MV sparks. It is suspected that similar runaway mechanisms occur in the laboratory sparks, natural lightning and TGFs.
The group has been monitoring TLE in the Southern Caribbean since 2009 and confirmed the occurrence of GJ, while satellites confirmed a high density of TGFs. In preparation for the flight stage of ASIM, in this project the group is extending the capabilities of the EVL to that region during 2014/15 project to learn about the electrical charge configuration and lightning altitudes inside tropical thunderstorms and to benefit optimally from the combination of climatology, satellite coverage and advanced lightning research technology. The key themes for TGF are the identification of the source lightning processes (leaders, strokes, or possibly initiation) and the influence of source altitude, and the possible coupling in space and time with TLE. For GJs, there is large potential for scientific impact during the scheduled campaigns with high-speed cameras that resolve their intricate dynamics for the first time.
The group will continue studying the storm conditions, lightning activity and parent lightning related to the TGFs observed by the current RHESSI and AGILE satellites. In the EVL, the group will be focus on obtaining high speed video images of TLE over the LMA network in order study the mechanisms of lightning related to the TLE dynamics. The group will also study the broadband radio emissions from TLEs parent lightning. In the findings on the TGF source, the group will continue investigating the energetic radiation of lightning and laboratory sparks. The group will devote its efforts to the study of the runaway processes of streamer/leaders and its microwave radiation.