Blue Jets Observations

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Blue Jets Observations Modeling

• Gennady Milikh, University of Maryland, College
  Park, MD, USA
• Presented at the workshop on streamers, sprites,
  leaders, lightning from micro- to macroscales
  October 2007, Leiden

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Discovery of Blue Jets

• Blue Jets or narrowly collimated beams of blue
  light propagating upwards from the top of
  thunderstorms were discovered during the
  Sprites94 aircraft campaign by the University of
  Alaska group.
• In their first paper Wescott, Sentman, Osborne,
  Hampton, and Heavner GRL, 1995 reported their
  findings

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Blue Jets Discovery

• Beams of blue light that propagate upward from
  the tops of thunderclouds at gt18 km.
• Narrowly collimated with an apparent fan out
  near the terminal altitude (40-50 km).
• Velocity 80-115 km/s.
• Intensity 0.5 MR.
• Brightness decays simultaneously along the jet
  after 0.2- 0.3 s.

Wescott , Sentman, et al., 1995 Sprite 94 Campaign
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The color of Jets

• Main spectral bands are 1P of N2 (478-2531 nm),
  2P of N2 (268-546 nm), and 1N of N2 (286-587
  nm).
• Volume emission rate is due to the electron
  excitation of the air molecules and collisional
  quenching.

• The red-line emission is strongly quenched below
  50 km, thus Red/Blue ratio ltlt1

5
More jet observations Reunion island 03/97,
from Wescott et all., 2001
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Blue Jet structure Wescott,et al., JGR,
2001

• At the base of the jet the diameter 400m.
• The diameter does not vary till 22 km.
• At 27 km it broadens to 2 km, and is 3 km at 35
  km.
• Eight smaller streamers with 50-100 m diameter
  detected.
• Lifetime of the event 0.1 s.
• Was not associated with any particular CG
  lightning.
• The total optical brightness reached 6.7 MR (0.5
  MJ of optical energy).

3km
2km
50-100m
0.4km
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Blue Starters (vertically challenged jets)
The starter extending upward to 25 km
Wescott, Sentman, Heavner et al., GRL, 1996
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Blue Starters
Wescott et al., 1996 2001

• Distinguished from Jets by much lower terminal
  altitudes 20-25 km.
• Apparent speed 27 to 150 km/s.
• Ionization 3 (427.8 nm).
• Arise out of the anvil during a quiet interval ?
  no coincidence with simultaneous CG flashes of
  either polarity. Occur in the same area as CG
  flashes.
• Associated with hail and updrafts (on a few
  occasions).

• Abrupt decrease in the cumulative distribution of
  -CG flashes for 3 s after the event.

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Gigantic Jets
Discovered by Pasko et al. 2002

• Wavelengths 350-890 nm
• 33-ms frames show two-trunk tree with filamentary
  branches.
• Fast growth of the left trunk within 33 ms.

• Two lt17-ms steps (1) Left trunk? 2 branches up
  to 70 km (2) Right trunk? tree sprite.

• A.Speed 50 km/s 1--5, 160 km/s (5-6), 270
  km/s 6--7

• Above the transition altitude of 40 km resemble
  sprites.
• Termination at 70km ? Edge of the ionospheric
  conductivity?
• VLF (sferics) polarity during re-brightening
  1825? upward negative breakdown ( CI).
• No apparent association with CGs.

gt2200 km/s 8.1--8.2

• A.Speed gt1900 km/s 7--8.1

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More Gigantic Jets
Su et al., 2003

• Stages Leading J, fully developed J (tree
  carrot), and trailing J.
• Leading Jet Emerging point 221-182-244 km (the
  top of the convective core), duration 34 ms,
  speed 10001-12004 km/s.
• Fully developed Jet Lifetime 171 - 1674 ms, a
  hybrid of BJ and sprite.
• Trailing Jet Duration 2331 - 3672 ms, speed 261
  - 1204 km/s, terminal altitude 601 - 684 km.

• Red circle? Thunderstorm convective core with the
  top at 16 km at 1431 UT.
• White lines Range of the line-of-sight to the GJ
  centre.
• GJ events 140918, 141159, 141515, 142001,
  and 142054 UT
• Wavelengths 400-1000 nm

• subsequent VLF ? CI breakdown with the charge
  moment change 1.7-2 kCkm (tree J15) and 1
  kCkm (carrot J24). No CG strokes associated
  with GJ were detected in the thunderstorm.

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• Summarizing characteristics of Jets/Starters
• Emanate from the tops of the electrical core of
  thunderstorms as faint blue cones of light that
  propagate upwards at speeds of 100 km/sec .
• Resemble a toll tree with a thin trunk and the
  branches on the top.
• 3. Termination altitude is 50 km (jets), 30 km
  (starters), 70-90 km (gigantic jets).
• 4. Are not associated with cloud-to-ground
  lightning discharges.
• 5. Occur much less frequently than sprites,
  although sampling bias may play a role in this
  assessment since observations are more difficult.

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Continuation 6. Brightness of jets exceeds 1
MR. 7. The rate of -CG flashes drops during 3 s
after the event. Is it a disruption of the
thunderstorm circuit? Why the gigantic jets
appear in thunderstorms occur over the ocean, not
in that occur over the land?
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Intermission
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Models of Blue Jets

• The earlier models suggested that BJs are either
  gigantic positive streamers Pasko et al., 1996
  or negative streamers Sukhorukov et al., 1996,
  such model require enormous charge of a few
  hundred C, and unable to explain the low
  propagation velocity.
• A beam of runaway electrons Russel-Dupre and
  Gurevich, 1996 has the same problem.
• Recently Petrov and Petrova 1999 and Pasko and
  George 2002 assumed that Jets are similar to
  the streamer zone of a leader.

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Leader-streamer structure of jets

• 1. Apparently the leader tip is the source for
  most streamers which form the upper part of a
  jet. Such leader is presented at blue jet photos
  as a long trunk from which branches grow.
• 2. The necessity of the leaders existence in a
  jet is caused by two reasons
• 2.1. At the altitude of about 18 km cold plasma
  decays in 10 ?s. Such source cannot supply jet
  streamers with the current during its lifetime of
  0.3 s.
• 2.2. In the absence of a leader, unrealistically
  high charges from the thundercloud are required
  to sustain streamers field.

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A Laboratory Leader

• In a leader channel the gas is heated above
  5,000K, thus maintaining its conductivity as in
  an arc channel.
• The leader tip continuously emits a fan of
  streamers at the rate of 109 1/s, which forms the
  streamer zone, and the current heats up the
  leader channel. Space charge of the stopped
  streamers covers the leader channel which
  prevents its expansion and cooling.

The key problem is how a self-consistent E-field
in the streamer zone is formed.
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Jets as a fractal tree Pasko and George, JGR,
2002

• Jets are similar to the streamer zone of a leader
• Starting from the point base the positive
  streamers are branching, as described by the
  Niemeyers algorithm 1989
• The E-field is generated by the branches and the
  cloud charge
• The scaling law is applied Es/Nconst, Es is
• from the laboratory experiments
• The model simulates the propagation of branching
  streamer channel.
• It shows transitions from starters to jets when
  the cloud charge increases

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• It resembles blue jets in terms of their
  altitude and conical structure.

• The model does not have the electron sink due to
  recombination and attachment
• The charge is collected by hail, which is a slow
  process. Similar problem of insufficient current
  supply in conventional lightning was resolved
  using concept of bi-leader Kasemir, 1960.

Recently Tong et al., 2005 used a similar model
but for negative streamers and get jets at 300
C.
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Jet model by Raizer et al. 2007

• A bi-leader forms in thundercloud. The positive
  leader moves upward forming the trunk of the
  observed tree while its streamer zone forms the
  branches.

• ES required to sustain streamer growth N.
  Thus long streamers grow preferentially upward,
  producing a narrow cone.

• Due to the transfer of thundercloud potential by
  the leader, the Jet streamers can be sustained by
  a moderate cloud charge.

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Numerical model of streamersRaizer et al.,
2006, 2007

• The model describes
• The motion of the streamer tip.
• The potential of the streamer tip versus its
  radius, electron density, and current.
• Electrical processes in the streamer channel
  including attachment and recombination.

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Output of the model

• Proven that the similarity law E/Nconst holds in
  the atmosphere at hgt18 km.
• Streamer propagation in the exponential
  atmosphere was described.

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• Despite a progress in understanding of the
  physical mechanisms leading to Blue Jet formation
  and propagation some outstanding problems remain
  unresolved such as how a self-consistent E-field
  in the streamer zone is formed.

• Further progress depends on the development of
  leader / streamer models based on the laboratory
  experiments.

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Atmospheric effects due to Blue Jets

• Blue jets can produce perturbations of the ozone
  layer Mishin, 1997.
• Can effect the atmospheric conductivity
  Sukhorukov Stubbe, 1998.
• Gigantic jets could produce a persistent
  ionization which recovers over minutes. Such
  recovery signatures may be observable in
  subionospheric VLF data Lehtinen Inan, 2007.

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References Kasemir, H.W. (1960), J. Geophys.
Res., 65, 1873-1878. Niemeyer, L., L. Ullrich
and N. Wiegart (1989), IEEE Trans. Electr.
Insul., 24, 309-324. Pasko, V.P., M.A. Stanley,
J.D. Mathews, U.S. Inan, and T.G. Woods (2002),
Nature, 416, 152-154. Pasko, V.P. and J.J. George
(2002), J. Geophys. Res. 107(A12), 1458,
doi10.1029/2002JA009473. Pasko, V.P., U.S. Inan
and T.F. Bell (1996), Geophys. Res. Lett., 23,
301-304. Petrov, N.I., and G.N. Petrova (1999),
Tech. Phys., 44, 472-475. Raizer, Y.P., G.M.
Milikh, M.N. Shneider and S.V. Novakovski (1998),
J. Phys. D. Appl. Phys. 31, 3255-3264. Raizer,
Y.P., G.M. Milikh, and M.N. Shneider (2007), J.
Atmos. Solar-Terr Phys., 69, 925-938. Roussel-Du
pre, R. and A.V. Gurevich (1996), J. Geophys.
Res., 101, 2297-2311. Su, H.T., R.R. Hsu, A.B.
Chen, et al. (2003), Nature, 423. Sukhorukov,
A.I., E.V. Mishin, P. Stubbe, and M.J. Rycroft
(1996), Geophys. Res. Lett., 23, 1625-1628. Tong,
L., K. Nanbu, and H. Fukunishi (2005), Earth
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Sentman, D. Osborne, D. Hampton, and M. Heavner
(1995), Geophys. Res. Lett., 22,
1209-1212. Wescott, E.M., D.D. Sentman, et all.,
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(2001), J. Geophys. Res., 106, 21,549-21,554.