The Physics of Lightning Flash and Its Effects

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• The Physics of Lightning Flash and Its Effects

COST Action P18 2005-2009 Chair Rajeev
Thottappillil, Sweden Vice-chair Farhad Rachidi,
Switzerland Web www.costp18-lightning.org 19
COST countries and 4 non-COST countries
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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.
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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.

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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

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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).

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Measurements using Rocket-triggered lightning
University of Florida, Gainesville, USA
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Measurements at Gaisberg tower, Austria
(This tower is struck by lightning on average 65
times in a year)
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Lightning return stroke

• Peak current 2000 A 300 000 A
• Average speed 1-2x108 m/s
• Typical maximum current rate of rise 100 kA/?s
• Channel radius 1-2 cm
• Channel temperature 30000 K

Saturation level
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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 (100-200 A for
  gt40 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?

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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.

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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?

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Production of the trace gas species in the
atmosphere by the hot plasma channel and corona
in lightning discharge
At global scale, lightning as NOx source
represent 10-30 of total.
R1 O2 ? O O R2 O N2 ? NO N R3 N O2 ?
NO O R4 NO O3 ? NO2 O2 R5 NO2 O ? NO
O2 Net O O3 ? 2O2
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 NOx?
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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?

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

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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.

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WG5 Mesospheric transient luminous events
associated with lightning
Lightning initiation of transient luminous
events, called sprites, elves, and blue jets, in
the mesosphere and ionosphere
A new topic. First observation in 1990. 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?
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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