Modelling electric fields above thunderstorms produced by tropospheric and high-altitude lightning discharges

1
Modelling electric fields above thunderstorms
produced by tropospheric and high-altitude
lightning discharges

• Anna Odzimek
• University of Leicester, UK
• Michael J. Rycroft, CAESAR Consultancy,
  Cambridge, UK,
• and University of Bath, UK
• Oscar van der Velde,
• Universitat Politecnica de Catalunya, Terrassa,
  Spain

Session 1 Thunderstorms and Lightning
Workshop on Coupling of Thunderstorms and
Lightning Discharges to Near-Earth Space Corte,
Corsica, 23 - 27 June 2008
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TLE Workshop, Session 1 Thunderstorms and
Lightning Corte, 23-27 June 2008
Modelling with PSpice

• PSpice is a computer program dedicated to
  simulations of electrical and electronic
  circuits.
• It can solve equations, including differential
  and nonlinear.
• Uses built-in models of electric elements such as
  resistors, capacitors etc., or electric switches.
• It could be used to model various phenomena.
• Modelling thunderstorm phenomena with PSpice
  seemed appropriate.
• We currently use PSpice A/D from the software
  package OrCad Unison Suites version 10.3.

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TLE Workshop, Session 1 Thunderstorms and
Lightning Corte, 23-27 June 2008
Positive CG discharges PSpice simulation
Rycroft et al. 2007
(1-D) Model thunderstorm and model circuit with
switches for the simulation of cloud-to-ground
(CG) lightning discharges
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TLE Workshop, Session 1 Thunderstorms and
Lightning Corte, 23-27 June 2008
Mesospheric effects of CGs
Time after CG and altitude where threshold
fields Eb, En and Ep are exceeded
RS
RSCC
2 kA
30 kA
50 kA
110 kA
Note the effect of electric field on
conductivity (and subsequently current flow and
electric fields) not taken into account
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TLE Workshop, Session 1 Thunderstorms and
Lightning Corte, 23-27 June 2008
Two populations of sprites Columns and Carrots
Conclusions of e.g. Stanley et al., GRL, 1999
McHarg et al., GRL, 2007, EuroSprite

• Column sprites
• Initiated at high altitudes (75-80 km)
• Streamers propagate downwards
• Carrot sprites
• Initiated at lower altitudes (65-75 km)
• Streamers propagate both downwards and upwards
• More delayed (by up to tens of ms)

Sprites on 17 August 2006 (EuroSprite images)
EuroSprite observations confirm these
conclusions they also suggest that column
sprites tend to be associated with stronger
positive CG strokes, while carrot sprites follow
weaker CG strokes, and that continuing currents
play a role
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TLE Workshop, Session 1 Thunderstorms and
Lightning Corte, 23-27 June 2008
Two populations of CGs current characteristics
CG type A 110 kA return stroke current (RS) no
continuing current Transfers 20 C to ground
CG type B 30 kA return stroke current (RS) 90
ms, 2 kA continuing current (CC) Transfers 70
C to ground
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TLE Workshop, Session 1 Thunderstorms and
Lightning Corte, 23-27 June 2008
Two populations of CGs - mesospheric effects
Time after CG and altitude where threshold
fields Eb, En and Ep are exceeded
Sprite type A (column-like) initiated at 80 km
altitude 1 ms after the onset of RS
Sprite type B (carrot-like) initiated at 65 km
altitude 10 ms after the onset of RS
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TLE Workshop, Session 1 Thunderstorms and
Lightning Corte, 23-27 June 2008
SPRITE discharge PSpice simulation
1-D model thunderstorm and sprite area - model
circuit with CG and similar sprite switches
controlling the discharges
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TLE Workshop, Session 1 Thunderstorms and
Lightning Corte, 23-27 June 2008
Two populations of CG/SPRITES electric field
profiles
CG 110 kA RS, followed by Sprite A (Column)
from 80 km to 45 km
CG 30 kA RS, 2 kA CC, followed by Sprite B
(Carrot) initiated at 65 km and expanding
downwards to 45 km and upwards to 80 km
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TLE Workshop, Session 1 Thunderstorms and
Lightning Corte, 23-27 June 2008
Larger thunderstorm with a positive charge layer
at 5 km - mesospheric effects
110 kA RS 2 kA CC
E - profile
30 kA RS 2 kA CC
V - profile
E profiles (log)
E- thresholds
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TLE Workshop, Session 1 Thunderstorms and
Lightning Corte, 23-27 June 2008
JET following a -CG lower atmosphere effects
(attempt of reproduction the Krehbiel et al.
example 1 - very recent simulation)
Q - profile
V profile
E profile
Krehbiel et al., Nature, 2008
Evolution after CG (30 kA RS) and a small jet
10-14 km, rJET 1 km ?Vion 1V Negative
discharge
E profiles (1 ms, 1001 and 1040 ms after the
-CG, here jet starts after 1s)
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TLE Workshop, Session 1 Thunderstorms and
Lightning Corte, 23-27 June 2008
Conclusions

• The presented model of a thunderstorm has its
  advantages (using electric elements and solving a
  circuit made by the programme, thunderstorm
  connected to the rest of global circuit) and
  disadvantages (not self-consistent, discharges
  forced, maybe too small resolution, too low
  dimension).
• Simulation imply qualitatively that very strong
  CG stroke produce enhanced field at the bottom
  of the ionosphere from 0.1 to 1 ms after CG
  initiation. This can lead to a column sprite
  discharge initiated at 80 km altitude 1 ms
  after the discharge onset. A moderate CG
  followed by a 2 kA (strong) continuing current
  lasting for several tens of ms produces
  significant enhancements after 10 ms. Perhaps
  this can lead to a carrot sprite initiated at 65
  km expanding both downwards and upwards.
• A small upward jet following a CGs discharge as
  observed by Krehbiel et al. is a negative type of
  discharge which can increase the ionospheric
  potential by 1 V.
• Questions how the model should be developed and
  what should be improved in the first place? Can
  discharges be simulated by electric switches at
  all? Or have the changes of the electric
  potentials and fields to be calculated
  self-consistently, using electric-field dependent
  variations, and is it enough for this purpose?

Anna Odzimek acknowledges funding from the EC WP7
programme People through the Marie Curie
European Reintegration Grant No.
PERG-GA-2007-203298