Transcript presentation

THUNDERSTORMS AND
LIGHTNING
GENERATING SPRITES
Rumjana Mitzeva
Outline
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Thunderstorms and lightning
Field observations and results
Physical mechanism
Outstanding problems
Answer to questions
• What is the relation between lightning and sprites?
• Which types of thunderstorms produce sprites and in
which part?
• Which conditions are conductive (favorable) for the
required lightning activity in these regions?
• Why?
• How do these microphysical conditions develop?
Transient luminous events (TLEs)
Optical signatures of
electrical breakdown
in the upper
atmosphere due to
rapid charge
rearrangement in
underlying
thunderclouds
(Adapted from Lyons et al. 2000)
ORDINARY THUNDERSTORMS
Negative CG lightning
Thunderstorms and Lightning
a) Stratiform region of
MCS
- Positive CG spider
lightning
b) Ordinary thundercloud
- Negative CG lightning
c) Tilted thundercloud
- Positive CG lightning
d)Supercell thunderstorms
with inverted polarity
- Positive CG lightning
Field Studies
• USA – 1994, 1996 – first field study
• USA - Severe Thunderstorm Electrification and
Precipitation Study (STEPS) - High Plains, near the
Colorado-Kansas border May – J uly 2000
• EUROPE - first field study 2000
• EUROSPRITE – start 2003–2006 - Southern Europe and
South Africa
• Brazil Sprite Campaign – 2002-2003
• Chile - Argentina – January 2005
• Spain - Catalonia 2003, 2004
• Japan – over Sea of Japan in Winter
• Bulgaria - ?
First analyses
• Boccippio et al., 1995 - Analyzed 42 sprites in July 12,
1994 and 55 sprites on September 7, 1994 +CG
lightning precedes most sprites (85%) by
approximately 20-30 min
• Sabbas [1999] studied 746 sprite events from 7 days
from the Sprites’96 Campaign, 75% of sprites were
preceded by +CG lightning.
STEPS
Severe Thunderstorm Electrification and Precipitation Study
High Plains, near the Colorado-Kansas border
May-July 2000
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Colorado State University, Fort Collins, CO
National Center for Atmospheric Research, Boulder, CO
National Weather Service, Lincoln, IL
South Dakota School of Mines and Technology, Rapid
City, SD
Colorado Climate Center, Fort Collins, CO
New Mexico Institute of Mining and Technology, Socorro,
NM
FMA Research, Inc., Fort Collins, CO
National Severe Storms Laboratory, Norman, OK
EUROSPRITE 2003
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Danish National Space Center, Juliane Maries Vej 30,
Copenhagen 2100, Denmark
Oersted-DTU, Danish Technical University, Kgs.
Lyngby, Denmark
'Commissariat Energie Atomique, Bruyeres-le-Chatel,
France
Department of Physics, University of Crete, Heraklion,
Greece
Laboratoire d'Aerologie, Universite Paul Sabatier,
Toulouse, France
Space Telecommunications and Radio Science
Laboratory, Stanford University, Stanford, USA
Geodetic and Geophysical Research Institute, Sopron,
Hungary
Space Physics Research Institute, University of Natal,
Durban, South Africa
Type of measurements
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Multiple-Doppler and polarimetric radar network
Time-of-arrival VHF lightning mapping system
Research aircraft
Electric field meters carried on balloons
Instruments to detect and classify transient luminous
events over thunderstorms
RESULTS
from STEPS
• More than 1200 transient luminous events (TLEs; mostly
sprites)
• Sprite parent +CG flashes, most often within the stratiform
precipitation region of larger MCSs
• Sprites typically accompany only a small percentage of
+CG flashes
• Supercells rarely produce sprites, except during their
dissipating stage, as stratiform debris cloud develops
• M=600 C-km – 10% probability of sprite occurrence
• M>600 C-km – 90% probability of sprite occurrence
STEPS
• Charge reservoir for SP+CGs would be found within
the lower portions of the MCS stratiform region
• Large charge moment Mq values appear to be
necessary, though perhaps not sufficient condition
for sprite generation.
EUROSPRITE 2003
• Similar results to STEPS +
• Infrasound from sprite – first clear identification
• Sprites generated by intra-cloud lightning - first
detections
• No signatures of relativistic electrons were identified
Sprite Parent Thunderstorms
In Summer
• Stratiform regions of mid latitude Mesoscale
convective systems (MCSs) -150 km2
• Mature and dissipating organized convection
• Not found over ordinary isolated thunderclouds
In Winter
• Over Sea of Japan
Sprite Parent Lightning
• Mainly positive CG lightning spider lightning
• Charge moment greater than 500 C-km
• Total charge transfer > 100 C
Physical mechanisms of sprite
generation
Wilson, 1925 - the electrostatic
field change of the lightning
flash is sufficient to exceed
the dielectric strength of the
mesosphere and initiate the
sprite – electrical breakdown
The critical lightning source
property is the vertical
charge moment — the
product of total charge
transfer and the height above
ground from which the
charge is removed.
Electron runway breakdown versus conventional
electrical breakdown
Why +CG lightning in stratiform regions of
MCS generates sprites?
• +CG - larger lightning charge moment
• +CG - longer duration of the parent lightning
currents
• -CG frequently exhibit multiple strokes, each with
current cutoff and no continuing current, whereas
+CG flashes frequently show single-stroke behavior
with a continuing current
Polarity asymmetry
• Mobility
contrast
between
electrons and positive ions
• Threshold
for propagation of
“+” end < for “-” end
• Mobile electrons are convergent
on one end (the ‘easy’ direction)
and divergent at the other (‘hard’
direction)
CONCLUSIONS
Sprites are thought to be generated by the electric
field pulse that travels upward toward the
ionosphere predominantly from a positive cloudto-ground (+CG) stroke of lightning from
stratiform regions of MCS - often by spider
lightning
Outstanding questions
• Conventional electrical breakdown or runway
electrons?
• Why mainly positive lightning in stratiform
regions of MCSs generates sprites?
• Do sprites and jets affect the atmosphere altering greenhouse gas concentrations in the
stratosphere and mesosphere or modulating
the atmospheric electric circuit.
EUROSPRITE CAMPAIGN 2006
References
• Barrington-Leigh, C.P., U.S. Inan, M. Stanley, and S.A. Cummer,
Sprites directly triggered by negative lightning discharges,
Geophys. Res. Lett., 26, 3605-3608, 1999.
• Boccippio, D., Williams, E., Heckman, S., Lyons, W., Baker, I.,
Boldi, R., 1995. Sprites, ELF transients, and positive ground
strokes. Science 269, 1088.
• Cummer S. , 2003: Current moment in sprite-producing
lightning, J Atm.spheric and Solar-Terrestrial Physics 65 ,499 –
508
• Cummer S and Walter A. Lyons,2004:Lightning charge moment
changes in U.S. High Plains thunderstorms, GRL, v. 31, L05114,
doi:10.1029/2003GL019043
• Cummer s. and al., 2005: Characteristics of Sprite-Producing
Positive Cloud-to-Ground Lightning during the 19 July 2000
STEPS Mesoscale Convective Systems, GRL, VOL. 32, L08811,
doi:10.1029/2005GL022778, 2005
• Gerken A. and U.Inan, 2004: Comparison of photometric
measurements and charge moment estimations in two spriteproducing
storms,
GRL,
V.
31,
L03107,
doi:10.1029/2003GL018751
• Lyons et al., 2003: Characteristics of Sprite-Producing
Positive Cloud-to-Ground Lightning during the19 July 2000
STEPS Mesoscale Convective Systems, Mon Wea Rev, v.131.
p.2417-2427
• Wilson, C.T.R, The electric field of a thundercloud and some
of its effects, Proc. Roy. Soc. London, 37, 32D, 1925.
• Williams, E., E. Downes, R. Boldi, W. Lyons and S.
Heckman, The polarity asymmetry of sprite-producing
lightning: A paradox, Preprint volume, 9-11, Conference on
Atmospheric Electricity, Brazilian Society for Electrical
Protection, Belo Horizonte, Brazil, November 7-11, 2004.