It is not easy to predict atmospheric phenomena such as lightning in the medium and long term. However, based on the experience acquired during more than 40 years of research on this phenomenon, the objective of this paper is to propose research topics on lightning that could be addressed in the coming decades to provide scientific answers and lay the foundations for technological innovations, currently unknown but that, with continuous, systematic, and rigorous work, will arrive. The future of lightning research could focus on four major topics: lightning in the intertropical zone, prediction, protection, and cloud-to-ionosphere lightning. Significant advances have currently been made in these areas, but it is necessary to delve deeper into them and work collaboratively with aerospace agencies such as NASA, the European Union, and global research groups that have already achieved excellent results in scientific interpretation and technological innovation.

Keywords: lightning prediction, lightning protection, cloud-ionosphere lightning

Modern research on the physics of lightning began in the early 20th century with the work of Wilson.¹ In the global circuit context, Wilson first suggested that electrified shower clouds played an equally important role to thunderstorms in the upward charge transport and maintenance of the global electrical circuit. Whipple² compared the diurnal variation in Brooks’ results³ and in the initial electric field measurements over the ocean, thus finding evidence that the global circuit contribution is dominated by a superposition of effects from three major zones of convection: tropical South America, Africa and the Maritime Continent (Southeast of Asia and Australia). More recent observations⁴ of the ionosphere’s potential and NASA satellite observations support this idea.⁵

Although tropical South America, Central Africa and the Maritime Continent areas were identified at the beginning of the 20th century as having high atmospheric electrical activity, the information available in the world on the characteristics and magnitudes of lightning was based mostly on studies carried out in semitropical or temperate zones, but scarce in Tropical Zones. Today there is better information about lightning in the tropics, thanks to the results of research in tropical countries such as Brazil and Colombia. But there is still a need to delve deeper into the subject of the intertropical zone.

This research work is very important to continue to statistically verify the variation of the lightning parameters such as the Keraunic level, the ground flash density, the lightning peak current etc., in the tropical zone, with respect to the temperate zone as in the USA, Europe or Asia.⁶ These results are fundamental for the design of protection against lightning and its statistical variation makes that the standards of temperate latitudes of protection again lightning, such as IEC62305, IEEE1410, EN50536 and others must take into account this spatial variation and thus mitigate the high mortality by lightning^7,8 or the high failure of electrical and electronic equipment⁹ that occurs in the tropical zone.¹⁰ Today in Colombia, for example, there are national technical standards that have been developed based on research results from the Colombian intertropical zone.¹¹

Research on lightning prediction

In the near future, lightning research will focus on lightning prediction, which will allow for risk reduction and protection in different productive sectors.

Based on the knowledge acquired about the lightning phenomenon, the PAAS-UN research group, through master's and doctoral work, has developed equipment that allows activity to be predicted approximately 30 minutes in advance. These systems can offer highly reliable predictions (90%), with a coverage radius of 20 km, and their operation is still isolated from that of other information systems. Some solutions can be achieved through further study of the data provided by these systems and their integration into storm tracking and prediction algorithms using Artificial Intelligence.

Electrostatic field sensors are among the most used thunderstorm detection devices in lightning warning systems. A field mill was designed and manufactured in the National University of Colombia^12,13 named PreThor. The main operational characteristics of the PreThor sensor are summarized in Table 1. Eight induction windows are periodically shielded by a metallic helix rotating at 2250 r.m.p. The 320 Hz output signal is digitalized at 100 kS/s using a resolution of 14 bits. Amplitude and polarity of the incident electrostatic field are computed by processing the digitalized signal; last process provides finally 5 samples per second of the measured electric field. The time stamp is provided by a GPS Garmin 18 x antenna.

Figure 1 shows the experimental field mill PreThor. It was inverted in order to reduce measurement interferences caused by the rain and nearby storms.

Figure 1 Figure 1 General scheme of lightning prediction with the equipment Electric field mill PreThor.

Research on lightning protection

Experiences on lightning control using lasers technology and lightning prediction systems: The development of a laser lightning rod could be an innovative tool to reduce the damages done by lightning on critical parts of electrical networks, nuclear power plants, or any other lightning-sensitive installation. The working principle of such a lightning protection system would be to create, during a thunderstorm, a long plasma channel by focusing a laser beam in the air above a tall grounded structure. This conductive plasma channel would then act as a path through which the lightning channel would develop, causing lightning to hit the chosen ground structure, and thereby preventing it from striking other nearby installations. In addition to protection purposes, this active lightning rod could also be useful to test the resistance to lightning of various equipment’s or simply be a powerful instrument for scientific investigation of lightning phenomena.^14,15

Since the 1970s, many researchers have studied the triggering and guiding of electrical discharges in laboratory with different types of laser systems.^16,17

Laser lightning protection is one of the applications of Laser Directed Discharges (LDD).¹⁸ Works are being performed in this direction.^19,20 However, its realization has a number of technical troubles. In particular, there are problems with lightning channel over commutation to LDD channel in case of the main type of lightning discharge - negative.¹⁹ Ultraviolet pulses of 200 fs duration and low energy (~ 0. 2m i) have a sufficiently high peak power to ionize oxygen and nitrogen by three- and four-photon ionization, respectively. It is shown that the resultant ionization channel induces a lightning like discharge at half of the natural self-breakdown voltage in nitrogen or air.²¹

Revel et al.¹⁹ report recent developments and tests performed using the ENSTA mobile, with the objective to sort out the main issues of using the femtosecond laser technology to develop active lightning protection system. According to this report, there are still questions to be answered about filamentation generation in real life conditions and it is necessary organize a measurements campaign to validate the lab results.

Cloud-ionosphere lightning research

Cloud-to-ground lightning is, to date, the electromagnetic phenomenon most widely interpreted by all civilizations in languages ​​such as myth, and in the last millennium it is the natural phenomenon most investigated by modern science. Unfortunately, some recent reports in the print media provide unreliable and misleading information about electromagnetic phenomena such as cloud-to-ionosphere lightning, describing them as "strange".

However, lightning generated between clouds and the ionosphere is an electromagnetic phenomenon that has only recently, nearly 30 years, been systematically studied worldwide. The focus of interest lies in very high-frequency radiation (gamma rays), which are very different from the rays studied so far in the radiofrequency range

The general phenomena known as Terrestrial Luminous Events (TLEs), which is divided into two major phenomena:  TERRESTRIAL GAMMA RAY FLASHES (TGF) and TRANSIENT LIGHT EVENTS (TLE) are currently being investigated by several research groups worldwide, including Colombia with the PAAS-UN group of the National University of Colombia.

The name Terrestrial Luminous Events (TLEs) is the generic name for a set of short-duration (milliseconds to seconds), very energetic phenomena observed in the Earth's atmosphere, between the stratosphere and the ionosphere (20-100 km) and associated with stormy areas with abundant lightning. However, the first records reported in the literature are from the 1990s.¹²

In 2011, a group of scientists presented a new scenario in an article published in Physical Review Letters²² based on space observations of the gamma radiation flux from thunderstorms (TGF). The analysis suggests that thunderstorms located in the upper layers of the atmosphere sometimes generate electron fluxes with energies exceeding 100 MeV. Figure 2 is the representation of TGFs and TLEs in space: Blue jets, red sprites, and elves.

Figure 2 Representation of TGFs and TLEs in space. Blue jets, red sprites, and elves.

Although the mechanism by which these high amounts of energy are produced is still unknown, they show that the propagation of energetic charges through the air acts as a kind of particle accelerator and therefore represents an energy source of inestimable proportions. Terrestrial gamma-ray flashes (TGFs) are high-energy particle emissions detected by Earth-orbiting satellites. NASA’s Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) mission, launched on 5 February 2002, demonstrated that a large proportion of TGFs are closely associated with tropical storm systems.²³

They have been given amusing names, such as "red sprites," "blue jets," and "green elves," which refer to their different shapes and colors (see Figure 1). They are discharged from the tops of storm clouds at the same time as lightning discharges within the clouds. "Red sprites" occur at mid-altitude in the atmosphere and are shaped like the stem of a carrot plant. Blue jets are pulses of light with flared ends, like the mouth of a trumpet. "Green elves" are almost invisible, flattened, jellyfish- or amoeba-like shapes that extend high into the atmosphere.

The impact of these events and their ability to generate NOx compounds is currently an open and active field of research. Future generations of researchers will ask many questions about cloud-ionosphere lightning that will advance scientific knowledge and provide the foundation for technological innovations regarding TLEs that are currently unknown. With continued, systematic, and rigorous work, these scientific truths will be revealed.

TLEs are therefore classified into three types:

Red Sprites,

Blue Jets, and

Elves,

The latter is called Luminous Sprites, a reference to Shakespeare's play A Midsummer Night's Dream. These phenomena are much more common than expected, occurring across the entire Earth's surface. They are associated with terrestrial areas with high atmospheric lightning activity, such as Colombia. They occur between the cloud layer and the ionosphere. Their morphology and dynamics are much more complex than expected. Their longitude distribution indicates that they are more frequent over continents, in tropical areas such as Colombia.

Ground-based gamma-ray flashes (TGFs) were discovered in 1994 by the Compton Gamma Ray Observatory, the second of NASA's Great Observatories, in honor of American physicist Arthur Holly Compton, Nobel Prize winner for his work in the field of gamma-ray physics. They are bursts of high-energy photons that originate in Earth's atmosphere in association with thunderstorms. It has been theoretically shown that as TGFs pass through the atmosphere, the large amounts of energetic electrons knocked out by collisions between photons and air molecules generate excited species of neutral and ionized molecules, generating a significant amount of optical emission. These emissions represent a novel type of Transient Luminous Event (TLE) in the vicinity of cloud tops. This predicted phenomenon has been shown to illuminate a region noticeably larger than the TGF source and to have detectable levels of brightness. The terrestrial origin of the intense bursts of Gamma GFR radiation discovered in the atmosphere is one of the mysteries of lightning physics that remain unsolved.

Since the discovery of gamma-ray emission in Earth's atmosphere, observations have linked the appearance of these emissions to the presence of lightning. The Atmosphere Space Interaction Monitor (ASIM) research project's mission aims to clarify this point.

The ASIM project was born to understand the electromagnetic phenomena TGF and TLE, which requires placing measuring instruments outside our atmosphere, in outer space, to study thunderstorms from above. The initial idea for the project dates back to 2003, promoted by the Technical University of Denmark. The main part of the project began development in 2010.

The main scientific objective of the ASIM project is to establish the spatiotemporal correlation between TLE, TGS, and cloud-to-ground lightning phenomena and to develop a unified model to explain their extraordinarily different frequency scales (1-100 cloud-to-ground lightning strikes per second, 1 TLE per hour?, 1 TGF per day?).

The Observatory Kit, located on the International Space Station since April 2018, will be dedicated to Earth observation in the optical, UV, X and wide-field Gamma ranges (in Gamma the entire Earth) with optical equipment equipped with high spatial resolution and very high temporal resolution (10-5 seconds) to make simultaneous and systematic observations of TGFs and LETs from space at about 400 km from Earth. These data are compared daily with data from the equipment located at the Dabeiba lightning research station in Barrancabermeja, Colombia.

The methodology proposed to contribute to the development of the ASIM project designs questions that will be answered through master's or doctoral theses, such as, for example, the identification of ground lightning hotspots in tropical regions such as Colombia, for application in communication towers, wind turbines, electric power towers, among others, or studies that contribute to a better understanding of electrification processes during storms in the tropics with equipment such as the Lightning Mapping Array - LMA and information from meteorological radars.

A first result of these investigations has been the height of the electric charge centers in the tropics, which varies spatially with latitude. For Colombia, a tropical region, the average electric charge height was calculated at 9.95 km, with a maximum height of 15.9 km. This average height is different from that found in the USA (Florida, semitropical region) between 10 and 12 km, and from that found in Japan, a temperate latitude: between 2 and 4 km.

A PhD thesis²⁴ presents the characterization of electrical structures and lightning leaders in thunderstorms and their relationship with terrestrial gamma-ray initiations (TGFs). The research provides detailed information on electrical charge distributions, their spatial boundaries, vertical development, lifecycle evolution, and the identification of charge centers and complex charge distributions.

Based on the results obtained,²⁴ it can be concluded that the interaction of a leader propagating at a height of 15 km with a potential of approximately 590 MV and under an electrical charge configuration composed of four layers, generating a negative electric field of approximately -874 kV/m, could be considered a scenario for the origin of TGFs.

The characterization derived from this doctoral thesis was of great interest, first, in the detailed study of electrical structures in tropical storms; second, in the analysis of lightning leader propagation in the tropics; third, it provided the spatial conditions and electrical charge configurations that were recreated through the development of a leader model; and finally, it contributed to the study of the electrical conditions favorable for the production of TGFs.

With information from the earth station in Barrancabermeja, Colombia, and that received from NASA's International Space Station, we follow the paths of the luminous elves, Elfos, who could shed light in the future on many questions and projects that have emerged from this research that has been going on for more than four decades in Colombia:

For example,

1. the relationship between the electromagnetic phenomena TGF and TLE with global warming,
2. the possibility of successfully completing Tesla's early 20th-century idea and patent on lightning and wireless electrical power transmission.²⁵
3. establishing the spatiotemporal correlation between these phenomena (TGF, TLE, and cloud-to-ground lightning) and developing a unified model that explains their extraordinarily different scales in terms of frequency (1-100 cloud-to-ground lightning strikes per second, 1 TLE per hour?, 1 TGF per day?),
4. investigating upward leaders originating from elevated structures on land in tropical regions, and the implications this will have on wind turbine protection,
5. identification of ground lightning hotspots in tropical regions such as Colombia, for application in communication towers, wind turbines, electric power towers, among others (MSc thesis completed in 2021).
6. measurement of Schumann resonance and ionospheric potential in the tropics.
7. studies that provide a better understanding of electrification processes during tropical storms using equipment such as the LMA and information from meteorological radars (MSc and PhD thesis completed in 2019).

In the future, more detailed studies of meteorological conditions during lightning leader propagation will be necessary using the LMA system and including information from meteorological radars, particularly in tropical regions. These types of studies would provide a better understanding of electrification processes during tropical storms.

These and many more questions and projects will provide scientific answers in the future and lay the groundwork for technological innovations that we don't know about today. However, with continuous, systematic, and rigorous work, they will arrive, because, as Sir Francis Bacon famously said, "Truth is the child of time, not of authority."

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1. Wilson CTR. Investigations on lightning discharges and on the electric field of thunderstorms. Philos Trans R Soc Lond A. 1920;221:73–115.
2. Whipple FJW. On the association of the diurnal variation of electric potential in the weather with the distribution of thunderstorms over the globe. Q J R Meteorol Soc. 1929;55(231):1–17.
3. Brooks CEP. The distribution of thunderstorms over the globe. Geophys Mem London. 1925;24:147–164.
4. Markson R. Tropical convection, ionospheric potentials, and global circuit variation. 1986;320(6063):588–594.
5. Williams ER, Rutledge SA, Geotis SG, et al. A radar and electrical study of tropical hot towers. J Atmos Sci. 1991;48(12):1386–1395.
6. Torres H, Chaparro J, Pérez E, et al. Contribution to lightning parameters study based on some American tropical regions observations. IEEE J Sel Top Appl Earth Obs Remote Sens. 2015;8(8):4086–4093.
7. Navarrete N, Cooper MA, Holle R. Lightning fatalities in Colombia from 2000 to 2009. Nat Hazards. 2014;74(3):1349–1362.
8. Cooper MA. Lightning injuries. In: Auerbach PS, ed. Wilderness Medicine. 5th ed. Mosby; 2007:67–107.
9. Interconexión Eléctrica S.A. (ISA). Annual report. Colombia; 1989. Spanish.
10. Torres H. Space and time in the lightning parameters, test on a research hypothesis. Research work presented to the National University of Colombia for promotion to Full Professor. Bogotá, Colombia; June 1998. Spanish.
11. Instituto Colombiano de Normas Técnicas y Certificación (ICONTEC). Colombian Technical Standard for lightning protection. NTC 4552. Bogotá, Colombia; 2009. Spanish.
12. Sentman DD, Wescott EM. Observations of upper atmospheric optical flashes recorded from an aircraft. Geophys Res Lett. 1993;20(24):2857–2860.
13. Castro JF. Methodology for identifying the typical electrical structure of lightning in the tropics. Master’s thesis. National University of Colombia; 2019. Spanish.
14. Comtois D, Vidal F, Desparois A, et al. Triggering and guiding of an upward positive leader from a ground rod with an ultrashort laser pulse—I: Experimental results. IEEE Trans Plasma Sci. 2003;31(3):377–384.
15. Torres H. Research project on lightning control using laser technology in Bogotá, Colombia. Draft version 1.0. Keraunos; January 2013.
16. Koopman DW, Wilkerson TD. Channeling of an ionizing electrical streamer by a laser beam. J Appl Phys. 1971;42(5):1883–1886.
17. Ball LM. The laser lightning rod system: Thunderstorm domestication. Appl Opt. 1974;13(10):2292–2296.
18. Vasilyak LM. Laser directed electrical discharges II. In: Proceedings of the Conference on Low Temperature Plasma PLTP–98; 1998; Petrozavodsk, Russia. vol. 2, p. 135–156.
19. Miki M, Wada A, Shindo T, et al. Basic study of laser–triggered lightning. In: Proceedings of the 10th International Conference on Atmospheric Electricity; 1996; Osaka, Japan. p. 656–659.
20. Uchida S, Shimada Y, Yasuda H, et al. Laser triggered lightning experiments in the field. In: Proceedings of the 10th International Conference on Atmospheric Electricity; 1996; Osaka, Japan. p. 660–663.
21. Aranguren D, Aponte J, Romero J, et al. Design, construction and calibration of two e–field machines used to measure tropical thundercloud e–field on the ground and aloft. In: Proceedings of the VIII International Symposium on Lightning Protection; November 21–25, 2005; Sao Paulo, Brazil. p. 184–189.
22. Tavani M, Marisaldi M, Labanti C, et al. Terrestrial gamma–ray flashes as powerful particle accelerators. Phys Rev Lett. 2011;106(1):018501.
23. Splitt ME, Lazarus S, Blakeslee RJ, et al. Thunderstorm characteristics associated with RHESSI identified terrestrial gamma ray flashes. J Geophys Res Space Phys. 2010;115(A9):A00E38.
24. Lopez JA. Investigation of electrical structures and lightning leaders in thunderstorms. Master’s thesis. Universitat Politècnica de Catalunya; 2019. Spanish.
25. Torres H. The Enigma of Electromagnetism Under the Microscope. Spanish Academic Publishing House; 2018.