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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - SAINT (Science and Innovation with thunderstorms)

Teaser

Summary

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.
New discharge processes in the atmosphere above thunderstorms have been discovered, the so-called Transient Luminous Events (TLEs) in the upper atmosphere, and Terrestrial Gamma-ray Flashes (TGFs) emitting particle beams of antimatter which are not properly investigated, neither in geophysics nor in the related fields of plasma and high-voltage technology.
These challenges are approached within the SAINT project with a coordinated program of research that includes satellite and ground observations with state-of-the art sensors in France and Spain, and modelling and lab experiments with excellent discharge diagnostics, leading computational modelling platforms and three upcoming space missions.

The overall objectives are divided into scientific research objectives and into technological research objectives:
a) Scientific research objectives:
- Identification of the generation mechanism(s) of TGFs and of their global occurrence rates
- Understanding lightning propagation and the effect of high-energy processes on lightning propagation by developing new computational models
- Characterization of the sub-processes of cloud discharges with unprecedented detail from measurements by a suite of novel sensors in space and on ground to develop

b) Technological research objectives
- Design of new tools for quantification of the chemistry of discharges: create instruments and models for the improved characterisation of the chemical reaction paths in atmospheric discharges for use in industrial applications (e.g. gas purification and ozone generation) and for quantification of the production of greenhouse gas constituents by lightning
- Design of new lightning detection approaches, i.e. algorithms enhancing data products from lightning detection systems in space and on the ground
- Design of new lightning protection/mitigation strategies by numerical models and instruments for wind turbines and aircraft

Therefore, the project aims to understand fundamental properties of lightning and its implications for society including plasma chemistry related to greenhouse gases and lightning protection.

Work performed

The project is divided into experimental, observational and theoretical work.

Out of 15 student projects, 5 started their projects in modelling, 6 on observations and 4 on laboratory experiments. During the first two years, three schools were organized training new, upcoming researchers and fostering collaborations between all participating partners.

Observational students started working on ground-based as well as on satellite data. Satellite data was explored using the Atmosphere-Space Interactions Monitor (ASIM) together with the Lightning Imaging Sensor (LIS) on the International Space Station. The analysis of terrestrial gamma-ray flashes (TGFs) relative to lightning activity required microsecond accuracy between the optical and x- and gamma-ray instruments which is now completed. More than 50 TGF events with simultaneous optical observations of lightning activity have been analysed and hundreds of events are ready for further studies allowing the identification of the lightning process that generates TGFs.
Parallel to the work with satellite data, observational campaigns were started. The first campaign was conducted in January 2018 by the University of Bath in collaboration with the South African National Space Agency at the Square Kilometre Array (SKA) site near Carnavon in the Karoo desert in South Africa. It was found that the site offers excellent optical observation opportunities for thunderstorms occurring in the north-east of South Africa near Losotho. In addition, the electromagnetic environment was found to be of an outstanding quality which offers novel opportunities for array measurements to be conducted during field work to study transient luminous events planned for 2020. Some first observations of TLEs with high speed cameras have been conducted.

In addition to observations, laboratory experiments were conducted. A set-up has been built which is able to measure discharge inception from metal and dielectric materials in unprecedented detail. It comprises of a vacuum vessel, a photo-multiplier, a high voltage pulse source, an ICCD-camera and electronics and software to enable automated measurements. Custom dielectric particles mimicking ice have been produced.

On the simulation side, a model to understand lightning attachment to wind turbines is developed. The emphasis of the study is in particular on density variations of the air flow near the blades, that can have an impact on the discharge evolution and hence on lightning inception. Another approach is to develop a computational model based on GPUs (Graphics Processing Units) rather than on CPUs (Central Processing Units) in order to simulate discharge processes. The new approach shows first promising results that can be tested against codes of other groups.

Final results

All sub-projects involved in SAINT are on the edge to deliver new, promising results:

Satellite and ground based data have revealed new, unprecedented data on lightning properties and their relation to transient luminous events (TLEs) and terrestrial gamma-ray flashes (TGFs) above thunderclouds.
In addition, experiments have shown first, promising results on lightning inception and computer models are at the frontier to a new generation of codes which will provide tools for the further study of discharge phenomena.

By the end of the project we expect
- to understand lightning characteristics and properties of TLEs and TGFs
- to understand lightning induced chemistry
- to understand which conditions facilitate lightning inception
- to develop new codes and to computationally study discharge phenomena
- to understand lightning attachment to moving shapes

Since lightning is still cause to hazardous events (e.g. at electric mills), it will be beneficial for society and its economy if we can understand lightning properties on a much more detailed level.