The Physics of Lightning Flash and Its Effects COST Action P Chair: Rajeev Thottappillil, Sweden Vice-chair: Farhad Rachidi, Switzerland Web: 19 COST countries and 4 non-COST countries

Split Workshop 2 Issues in lightning research 1) Phenomenology of processes in the lightning flash? 2) Lightning initiation in thunderclouds? 3) Lightning stepped leader and dart leader? 4) Lightning attachment to objects? 5) Lightning return stroke? 6) X-rays and gamma-rays emission associated with lightning? 7) Ball lightning? 8) Lightning initiation of transient luminous events, called sprites, elves, and blue jets, in the mesosphere and ionosphere? 9) Production of the trace gas species in the atmosphere by the hot plasma channel and corona in lightning discharge? 10) Inferring properties of lightning processes from remote measurements of electromagnetic radiation from lightning? No single group has expertise in all these issues.

Split Workshop 3 Scientific Programme The main objective of the Action is to increase our knowledge of the physics of the lightning discharge and of its effects on natural and man-made systems. Examples of natural system – climate, atmospheric chemistry, global electric circuit Examples of man-made system – electrical and communication networks, railway network, flying objects, buildings and other facilities. This part has relevance to EMC and COST 286. However, it is the physical basis of the lightning interaction that is dealt with within COST P18.

Split Workshop 4 Scientific Programme Division of research tasks (Work Groups) WG1. Measurement of properties of various types of lightning discharges WG2. Phenomenology and modelling of the processes in the lightning flash WG3. Physics and models for the lightning attachment to objects WG4. Inverse source problems in lightning WG5. Mesospheric transient luminous events associated with lightning

Split Workshop 5 WG1. Measurement of properties of various types of lightning discharges Emphasis on time-correlated measurements on the same lightning using diverse instruments (currents, electromagnetic fields, optical measurements, x-rays, gamma-rays) Time scale from nanoseconds to milliseconds Establishment of a data bank on the lightning parameters, including a databank on the characteristics of the electromagnetic radiation of lightning from ELF to gamma rays (could be beneficial for COST 286).

Split Workshop 6 Measurements using Rocket-triggered lightning University of Florida, Gainesville, USA

Split Workshop 7 Measurements at Gaisberg tower, Austria (This tower is struck by lightning on average 65 times in a year)

Split Workshop 8 Lightning return stroke Peak current: 2000 A – A Average speed: 1-2x10 8 m/s Typical maximum current rate of rise 100 kA/  s Channel radius: 1-2 cm Channel temperature: K M M M IC C Saturation level

Split Workshop 9 Lightning return stroke – conti. Why there are so large variations in the peak current, charge, and optically measured speed between return strokes? Why there is continuing current ( A for >40 ms) after some return strokes? Why some negative CG lightning flashes are single stroke flashes while majority of them are multiple-stroke flashes (1-26 strokes)? Why for some strokes there is more than one termination on ground, separated by a few meters to a few kilometres? A model for return stroke that could explain all the major observed characteristics. How is the physics of negative return stroke different from positive return stroke? Why positive lightning produces the most energetic return strokes, in terms of the largest value of peak currents and largest value of effective charge lowered?

Split Workshop 10 WG2. Phenomenology and modelling of the processes in the lightning flash Detailed analysis of the measurements carried out in WG1 will fill the gaps in our present understanding of the phenomenology of the processes. Models for various lightning processes: lightning initiation, stepped leader, lightning attachment, return stroke, continuing current, M component, K changes, and dart leader. To understand the mechanism of the production of the trace gas species in the atmosphere by the hot plasma channel and corona in lightning discharge. To understand the connection between the particular characteristics of lightning flashes and the associated observation of luminous events in the mesosphere and the lower ionosphere.

Split Workshop 11 x-rays and gamma-rays emission associated with lightning A new topic in lightning research. Very few reliable measurements. What processes in lightning give rise to these? What is the physics behind it?

Split Workshop 12 R1:O 2  O + O R2:O + N 2  NO + N R3:N + O 2  NO + O R4:NO + O 3  NO 2 + O 2 R5:NO 2 + O  NO + O 2 Net:O + O 3  2O 2 At global scale, lightning as NOx source represent 10-30% of total. Production of the trace gas species in the atmosphere by the hot plasma channel and corona in lightning discharge How the hot plasma channel of the lightning return stroke, and the corona produced during the pre-breakdown processes reacts with the molecules in air and produce trace gas species, most importantly NO and NO x ?

Split Workshop 13 WG3. Physics and models for the lightning attachment to objects Modelling the break-through phase (meeting between donward and upward leaders). What determines the striking distance? How striking distance is related to the measurable parameters like charge and current? Any difference in the attachment process when upward leaders are initiated from insulated objects (e.g., trees, rotor of windmills) as opposed to from grounded conducting objects (e.g., air terminals on top of buildings, towers)? What are the conditions necessary for a tall object (e.g., tall tower, mountain top) to initiate long upward leader all the way to the cloud, even when there are no visible downward leader prior to that? What is the physics of triggering of lightning by flying objects. How the struck medium (e.g., tall towers) could influence the return stroke parameters? What role surface arcs play in supplying the current (charge) involved in lightning return stroke?

Split Workshop 14 Lightning attachment to aircraft Bi-directional leader development Models for lightning initiation by flying objects and attachment to flying objects.

Split Workshop 15 Lightning attachment to objects – termination on earth Lightning current dissipation in soil. Surface arcing. Fulgurites production. First photograph of surface arcing (Triggered lightning, Sandia national lab., 1991) Evidence of surface arcing

Split Workshop 16 WG4. Inverse source problems in lightning What can we learn about lightning from its electromagnetic radiation (radio frequency, microwave, infrared, visible light, ultraviolet, x-ray and gamma ray regions of spectrum). Studying lightning discharge development inside clouds using interferometric and time-of-arrival of pulse techniques. Models for radio wave propagation over different kinds of terrain, to compensate for propagation effects.

Split Workshop 17 Inferring properties of lightning processes from remote measurements of electromagnetic radiation from lightning What can we learn about the physics of the processes in lightning by analysing its electromagnetic radiation (radio-frequency, visible light, x-rays, gamma rays)? Mapping the 3-dimensional evolution of lightning channels within clouds by tracing the sources of radio-frequencies using time-of-arrival and interferometric techniques.

Split Workshop 18 A new topic. First observation in What role lightning play in the initiation of transient luminous event? Often sprites are associated with large positive return strokes and blue jets with large negative return strokes. How this coupling works? Lightning initiation of transient luminous events, called sprites, elves, and blue jets, in the mesosphere and ionosphere WG5: Mesospheric transient luminous events associated with lightning

Split Workshop 19 Dissemination plan - audience Target audience: Researchers working with different aspects of the physics of lightning Other interested audience: International standard making bodies concerned with lightning protection National and regional policy makers and planners concerned with weather and environmental issues related to lightning Insurance industry and service providers concerned with risk of damages and accidents due to lightning Manufacturing and service industry concerned with effective lightning protection