Coordinated Measurements of Transient Luminous Events - SPRITES

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Coordinated Measurements of Transient
Luminous Events - SPRITES from the Space
Shuttle and Ground Stations during MEIDEX

• Zev Levin, Yoav Yair, Colin Price,
• Peter Israelevich, Adam Devir,
• Baruch Ziv, Joachim Joseph,
• Yuri Mekler, Meir Moalem

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The Global Circuit 1
Ionosphere
Precipitation
Earth
Fair weather field
250kV

• The atmosphere is like a spherical capacitor with
  the outside charged positively and the inside
  (ground) charge negatively.
• The potential difference between these two
  electrodes is about 250,000 Volts. Its average
  value remains fairly constant with time.

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The Global Circuit 2

• Although the atmosphere is a poor conductor an
  electrical current is continuously discharging
  the capacitor.
• The electric field starts at about 120 V/M near
  the ground and decreases exponentially with
  height. At heights above clouds it is normally as
  low as 1 mV/m.
• Lightning flashes are the generators that
  maintain the atmospheric electric field.

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The Charge Distribution in Thunderclouds
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Global Lightning Distribution for June 1999
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Lightning

• Lightning are much more common over land than
  over the sea.
• Most lightning strokes are inter cloud. They
  simply discharge the charge centers that have
  been developed.
• About 40 of all flashes are cloud to ground and
  most of these are negative bringing negative
  charge to ground.
• About 10-20 of the flashes to ground are
  positive positive charge to ground.
• The reason for these positive flashes is not yet
  known, but its frequency of occurrence is
  related to either the tilt of the clouds
  and/or to the size of the storms (large mesoscale
  convective systems).

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The ratio N PGF/NGF varies during the lifetime
of the storm. Sometimes N gt 1.
N0.3
Early part of the storm
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N0.52
Mature part of the storm
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N6.25
Decaying part of the storm
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SPRITES

• About 10 years ago, the Transient Luminous
  Emissions were first discovered and were given
  the names of Sprites (most common), Blue Jets and
  Elves.

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Sprites etc.
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Transient Luminous Events
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Red Sprites

• Usually associated with very strong PGFs (peak
  current gt 130kA, 77 probability).
• Stratiform region of MCS
• Initiate at 70-75 km, moves both up and down.
• Terminal height 85-90 km. Lifetime few msec.
  500 kR.
• Speed 107 m/sec.
• Illuminated Volume gt 104 km3.

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Blue Jets

• Not associated with PGFs, but occur in T-storms
  with intense NGF hail strong updrafts
• Terminal altitude 32-43 km, Speed 11224 km/sec.
  Ionized N2
• Not so rare, but hard to observe from the ground.
  10 MR

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Sprites from Space
17 events from payload-Bay cameras during the MLE
(Boeck et al, 1995) STS 34 (1989), STS 32
(1990), STS 31 (1990), STS 41 (1990)STS 43
(1991), STS 48 (1991), STS 46 (1991)
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Sprites observations with the MEIDEX cameras

• Primarily with the 665nm filter for Red Sprites
  and Elves and with the 380 and 470nm filters to
  record Blue Jets.
• Continuous recording of the Earths limb from the
  direction of the dusk terminator towards the
  night side, preferably before midnight local time
  at the observed area.
• The Astronaut will use the SEKAI LL-Video color
  camera to look for major thunderstorm centers.

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On-Orbit Operations and Ground Stations for
Sprite Measurements
Chile
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Configuration for Viewing Sprites
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Forecast of Sprites --forecast of regions of
strong convection and cloud top temp. of around
70C
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MEIDEX-Sprite ROIs
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The atmosphere as a wave guide
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Ground Observations Israel

• During the 16-day flight, two field sites in the
  Negev Desert in Israel will be used to collect
  ELF (SR) and VLF data related to sprite activity.
• Both are operated by TAU.

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Global Ground Observations

• Optical measurements Japan (Osaka, Sendai),
  Taiwan (Taipei), USA YRFS, Stanford (?)
• ELF measurements Long Island, Hungary,
  Antarctica
• VLF network Germany, S.Africa, Chile,
  California, New-Zealand, Japan USA (Duke)
• Lightning Location Systems Japan, Brazil, NLDN

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Summary

• Unique opportunity for global coverage
• Multi-sensor measurements
• The first ever spectral Calibrated measurements
  from space