SAINT is an educational platform within a dynamic and multidisciplinary scientific network of scientists developed through the CAL FP5 project, continued in the TEA-IS network of ESF, and leading to the European space missions of ASIM, TARANIS and the US mission ISS-LIS. The SAINT Training Program will support PhD education for 15 ESRs within the environment of 8 top-level universities, 8 industrial partners, and 3 agencies and research institutes. Each ESR will be enrolled in a Doctoral Programme.
Lightning is an extremely energetic electric discharge process in our atmosphere. It significantly affects the concentration of greenhouse gases, and it threatens electrical and electronic devices, in particular, when placed on elevated structures like wind turbines or aircraft, and when these structures are built with modern composite materials with inherently low electric conductivity. In addition, even our fundamental understanding of atmospheric electricity is far from complete.
Lightning above the clouds
New discharge processes in the atmosphere above thunderstorms have been discovered, the so-called Transient Luminous Events (TLEs) in the stratosphere and mesosphere, and Terrestrial Gamma-ray Flashes (TGFs) that can emit particle beams of antimatter. These phenomena are not properly investigated, neither in geophysics nor in the related fields of plasma and high-voltage technology where similar discharges appear.
Observations, simulations and experiments
These challenges are approached within the SAINT project with a coordinated program of research that includes satellite and ground observations, and modelling and lab experiments (mostly from a geophysical perspective, but with strong interfaces to plasma technology and relevant industries). The SAINT consortium integrates leading techniques from different disciplines to investigate fundamental mechanisms of atmospheric discharges. They include dedicated observation networks in Spain and France with state-of the art sensors, advanced high-voltage labs with excellent discharge diagnostics, leading computational modelling platforms and three upcoming space missions.
An array of space missions
Two missions are on the International Space Station (ISS), the Atmosphere-Space Interactions Monitor (ASIM) by the European Space Agency (ESA) in 2018 and NASA's Lightning Imaging Sensor (ISS-LIS) in 2017. The third is the Tool for the Analysis of RAdiatioN from lIghtning and Sprites (TARANIS) satellite of the French Centre National d'Etudes Spatiales (CNES) in 2019. The European missions are the first to carry dedicated instruments for simultanous observations of lightning, TLEs and TGFs, and represent an investment exceeding 100 M€.
An integrated approach
The SAINT project takes advantage of this extraordinary opportunity with a multidisciplinary and inter-sectorial training platform for 15 ESRs. The three missions are developed within separate space agencies and the exploitation of their data is currently uncoordinated. SAINT will integrate the data evaluation of the missions with ground observations, model development and lab experiments. An essential prerequisite is to overcome the significant interdisciplinary barriers (between atmospheric and space science, plasma physics and chemistry, instrumentation, engineering, modelling and scientific computing, as well as the inter-sector barriers, which currently hold back knowledge transfer between academic and industrial sectors and subsequent novel developments. A consortium formed of key players from these sectors will lead to breakthroughs in geophysical research as well as in discharge technology and protection.
Understanding atmospheric discharges
The atmospheric electric discharge is a fundamental process of nature that converts electric energy into ionization, radiation, chemical products and heat. Lightning causes perturbations to green house gas distributions that significantly influence the earth's radiation balance; they pose a threat to lives and to our increasingly vulnerable infrastructure based on sensitive microelectronics and on advanced materials and technology where discharges can have catastrophic effects. Electric discharges are also developed and used in many branches of technology. Although studied since the time of Jaques de Romas and Benjamin Franklin in the 18th century, much of lightning physics escapes quantification. A proof of point is the recent discovery that lightning can reach the ionosphere at ~80 km altitude, and can emit gamma-radiation and even antimatter.
The concentration and distribution of greenhouse agents in the atmosphere are affected by thunderstorms: Lightning is a major source of NOx, which plays a key role for ozone production. Understanding NOx production by lightning allows under-standing the possible feedback mechanisms between climate change and thunderstorms. However, in spite of many attempts, including aircraft campaigns as the EU-funded EULINOX and TROCCINOX projects, large uncertainties remain in the quantifica-tion of NOx produced by lightning because of the complexity of observations and modelling.
Water vapour and ozone
In addition, thunderstorms entrain surface air, including water vapour, pollutants and dust particles, transporting them to the upper troposphere where they have longer residence times and may spread over intercontinental distances transported by the strong winds in this region. Subsequent chemical transformation leads to perturbations to ozone concentrations and formation of aerosols which affect global climate and acid rain. Besides ozone, water vapor is an important greenhouse gas with a large effect on climate. Consecutively injected into the stratosphere by thunderstorms, water vapour increases ozone loss and UV dosage and entrains ozone-rich stratospheric air into the troposphere (a transport pathway for ozone missing in major global models).
Convection and upward flashes
Lightning is a proxy for the power of convection and thereby for chemical effects by lightning and redistribution of greenhouse gas agents in the atmosphere. Lightning protection requires a new approach for exposed, complex systems such as aircraft and wind turbines, because of their size, materials, and structural complexity, their operation and location and their critical electronic systems. For example, wind turbines are now so tall that they generate upward lightning from the nacelle and/or blades to thunderstorm clouds. The simplified approach to upward flashes by the International Electrotechnical Commission might result in an important underestimation of the actual number of lightning impacts. In addition, the presence of carbon-reinforced plastics (CRP) in the blades introduces new challenges to be considered during the coordination of the blade design with the lightning protection system (e.g. mechanical stress resulting from the energy dissipation in CRP laminates due to the circulation of currents).
The rise of carbon fibre materials
Carbon fibre composite materials are now common within the aviation industry, including cabins for the latest generation of aircraft. Their electric conductivity is generally smaller and more anisotropic than in metals, but lightning safety must remain at the same level as for fully metallic aircraft, creating new challenges for aircraft construction and subsequent testing.
The high-energy radiation of gamma-rays, electrons and positrons in lightning discharges (discovered as TGFs), could pose completely new lightning protection problems for aircraft, due to the eventual delivery of a large dose to aircraft electronic equipment within a few milliseconds. The radiation inside aircraft has been measured in recent aircraft experiments.
Lightning detection systems on the ground rely on the electromagnetic (EM) radiation from the lightning where a group of sensors measures the waveform and a common predefined signature identifies a lightning event. Operational grade networks are typically only sensitive to cloud-to-ground lightning and give the time, location, peak current and the multiplicity of strokes. Recent advances in network techniques include denser networks with ~25 km baselines that measure the full lightning discharge in 3 dimensions, including intra-cloud lightning, and networks with long distances (~1000 km) between sensors that measure global lightning activity, notably also over oceans and in less-industrialized countries without national networks. For all networks, considerable effort goes into the determination of their sensitivities.
Detection from satellites
A technique has also been developed that detects lightning optically from satellites. The vantage point of space gives a high detection efficiency of intra-cloud lightning and captures most lightning to ground. Optical detectors are planned for the next generation geostationary meteorological satellites of EUMETSAT and NOAA, building on the ISS-LIS technology. It is therefore of considerable interest to characterize the strong and weak points of lightning detection systems from ground and space and to study the potential which lies in their combination. It is also of interest to push the boundaries of current scientific knowledge further to identify underlying micro-processes of lightning and their signatures in sensitive detection systems.
High voltage technology
Discharges play a key role in plasma technology and in high-voltage engineering. The conversion of electric energy into chemical reactants within a discharge is widely used in spark plugs of car engines and in ozone generators for disinfection. Very actively investigated topics include plasma medicine, plasma assisted ignition and combustion, plasma processing and plasma assisted conversion of solar power into liquid fuel. In high voltage technology, corona discharges dominate energy losses along high voltage electricity lines and they are detrimental when short-circuiting insulating layers. They are also the key ingredient in electrical circuit breakers in our electricity nets where important questions are now how to replace the highly insulating SF6 gas by a less polluting medium and how to design circuit breakers for possible future dc electricity nets.
- NASA: Marshall Space Flight Center, USA
- Global Lightning Protection Service, Herning, Denmark
- Nowcast Lightning Detection, Munich, Germany
- PLASMA MATTERS B.V., Eindhoven, Netherlands
- Airbus, France
- Meteorage Lightning and Informations Systems, France
- Thales Services SAS, France
- University of Alabama, Hunstville, USA
- University of Granada, Spain