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High Time-Resolution Sprite Imaging: Observations and Implications. H. C. Stenbaek-Nielsen Geophysical Institute University of Alaska Fairbanks M. G. McHarg U.S. Air Force Academy. This ppt version was prepared for conference web site posting. - PowerPoint PPT Presentation
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Leiden October 2007
High Time-Resolution Sprite Imaging: Observations and Implications
H. C. Stenbaek-NielsenGeophysical Institute
University of Alaska Fairbanks
M. G. McHargU.S. Air Force Academy
Leiden October 2007
This ppt version was prepared for conference web site posting.
There are no animations in this version. Animations havebeen replaced with a representative image, and some additionalexplanatory text has been added.
I will be preparing compressed version of animations.(Most are too large for email)
Some are available with our publications through AGU’s journal website:McHarg et al. GRL, 34, L06804, doi:10.1020/2006GL027854, 2007Stenbaek-Nielsen et al., GRL, 34, L11105, doi:10.1029/2007GL029881, 2007
For further info contact us by email:[email protected]
Leiden October 2007
Trans Luminous Events (TLE)
Elve: 1 ms E&M pulse
Halo: 1-5 ms: glow discharge
Sprite: 1-10 ms; streamer discharge
Afterglow: 1-200 ms chem. processes
Blue jets, beads, crawlers, ambers etc.: 5-1000ms process ?????
Leiden October 2007
2 examples at 1000 fps
• Sprite dynamics• Images show features well known from TV
image sequences with better detail– Halo, tendrils, branches, and beads
• Images colorized for emphasis• Altitude scale derived assuming sprite to
be at lightning strike (NLDN)
Leiden October 2007
Sprite at 1000 fps
Sequence: 15 ms.
Selected frames from animationAnimation
Leiden October 2007
Sprite at 1000 fps
Sequence: 30 ms. Note: No halo with second sprite
Animation Selected frames from animation
Leiden October 2007
Rebrightening
Leiden October 2007
Features to be addressed
Time scales
← Branches < 1 ms(not resolved at ms)
← Beads/afterglow > 1 ms
←Tendrils < 1 ms (not resolved at ms)
Image: 18 Aug 1999, WIRO, Wy.
Leiden October 2007
Effect of frame rate9 July 2005 06:06:46 UT
Streamers (almost) resolved at 50 μs (20,000 fps)
33 ms video 1 ms 50 s
10,000 fps makes a lot of difference…..
Leiden October 2007
Link to streamers in the lab
Exposure: 300 ns 50 ns 10 ns 2 nsCourtesy of Prof. Ute Ebert and T. Briels of TU Eindhoven, Netherlands
Leiden October 2007
Scaling of process time
• Time development scales as 1/n
• Density at ground level: 3 1019 /cc• Density at 80 km altitude:3 1014 /cc
• Scaling factor: 105
Leiden October 2007
Scaled to 80 km altitude
30 ms (~TV) 5 ms 1 ms 0.2 ms 33 fps 200 fps 1000 fps 5000 fps
Leiden October 2007
Scaled to 80 km altitude
30 ms (~TV) 5 ms 1 ms 0.2 ms 33 fps 200 fps 1000 fps 5000 fps
10,000 fps makes a lot of difference…..
Leiden October 2007
Streamer head formation
• First downward, later upwards moving streamer heads
• Upward starts from– Lower altitude – Existing luminous
sprite structures
(animation: GRL, 34, 11, 2007)
9 ms image sequence
Animation
Leiden October 2007
Streamer head formation
9 July 2005 06:33:11 UT: 10,000 fps Gating 50 µs Duration 5.0 ms
Downward streamers first
Upwards streamers later and
- from lower altitude
- from existing structure
Streamer velocity up to 0.3 c
Animation
Leiden October 2007
Streamer head formation
Downward streamers first
Upwards streamers later and
- from lower altitude
- from existing structure
Streamer velocity up to 0.3 c
7 July 2005 08:31:20 UT: 5,000 fps Gating 100 µs Duration 5.0 ms
Animation
Leiden October 2007
Downward Streamer
• Summary of downward streamers:– Streamer head starts 70 - 90 km altitude– Halo may or may not be present– Streamer head brightens as it moves down– Direction largely straight down– Velocity up to 6 107 m/s– Both increase and decrease in speed
observed
Leiden October 2007
Upward Streamer
9 July 200504:15:17 UT 10,000 fpsAnimation
Leiden October 2007
Upward Streamer
• Summary of upward streamers:– Not present in all events– Starts later than downward streamers– Starts at lower altitude than downward streamers– Starts from bead structures– Ends with a “puff” and upward motion stops– Velocities similar to downward streamers– Significant horizontal velocity component
Leiden October 2007
Morphology
• C-sprite– Downward streamers– No upward streamers
• Carrot sprite– Downward streamers– Upward streamers
Leiden October 2007
Main Points
• All sprites start with downward moving streamer heads
• Streamer heads are small. Appear in images just like background stars
• Individual streamer heads move in one direction only
• No example of double headed streamers• No evidence of geomagnetic field effects
Leiden October 2007
Streamer head brightness
• Streamer heads:– Gaussian profile– Similar to stars Smaller than spatial
resolution Point sources Stellar mag -6
Emission rates:5 1021 to 3 1024 phot/s
Leiden October 2007
Size
• Smaller than our ~150 m resolution• Telescope obs: 10-200 m (Gerken et al.)• Models ~25 m (Liu and Pasko)
Assuming 25 m size:Average brightness: 1 – 100 GR
Leiden October 2007
Size
Assuming 8 1011 #/cm3/s (Sentman et al.):Size from 30 – 300 m
Leiden October 2007
Streamer brightness presented is in the June 16 issue of GRL.
Reprints available here at meeting
Leiden October 2007
Implications
• Streamer heads very bright– Source of energy for local chemical processes
(talk Friday by D. Sentman) – Longer lasting effects?– Significant effects on the mesosphere?
Leiden October 2007
Streamer head splitting
9 July 200506:33:11 UT 10,000 fps
Animation
Leiden October 2007
Streamer head splitting
• Splitting on the run• 2005 data show splitting a ‘slow’ process:
– Individual streamer heads propagate ~30 km, but only a few splitting events observed
– Only 1 or 2 new streamer heads formed in each splitting
– No ‘slow down’ while splitting• But 2007 telescopic images show many
and multiple streamer heads forming
Leiden October 2007
Streamer head splitting
• 23 June 2007 07:01:01 UT, Langmuir, NM• 10,000 fps, 50 μs exposures• Field of view: 2.12x1.58 degrees• Altitude 80 km at 600 km range• Velocity: 3 107 m/s; Size: ~0.1 to ~2 km
Animation
Leiden October 2007
Streamer head splitting
23 June 2007 04:22:49 UT10,000 fps, 50 μs exp.Field of view: 2.12x1.58 degAltitude 80 km at 600 kmVelocity: ~107 m/s; Size: ~0.1 to ~2 km
Leiden October 2007
Streamer head splitting
• Preliminary analysis• Difficult to match with
earlier larger FOV images– More splits– More streamer heads
• Maybe the sequences are from the central part of the sprite Animation
Leiden October 2007
Afterglow
9 July 200504:38:00 UT 10,000 fps
Leiden October 2007
Afterglow
• Very little spatial motion• Vertical structure and brightness not as
expected from streamer head brightness• Duration of afterglow vary between events• Energy beyond streamer heads alone• Can last from a few ms to several 100 ms• Total optical power may be larger than for
streamer heads
Leiden October 2007
Afterglow spectrum(300 fps)
N2 1P spectra. Some altitude differences indicating additional local processes (Kanmae et al., GRL, 2007).
Leiden October 2007
Streamer head spectrumSlitless spectroscpy
Star background. 0th and 1st order spectra clearly seen.
Wavelength coverage 400-900 nm
Leiden October 2007
Streamer head spectrum50 μs (20,000 fps)
Primarily N2 1P
Leiden October 2007
Atmospheric effects
Sprites were at 600-700 km so blue attenuated by ~x100
Leiden October 2007
Optical spectra
• Primarily N2 1P band emissions in both streamer heads and afterglow
• Spectral altitude differences in afterglow• No N2 ion emissions detected (yet)• Would expect differences between
streamer heads and afterglow (not proven yet – we are working on it)
• Chemical processes and their consequences
Leiden October 2007
Delayed Sprite
Video (30 fps). FOV: 21x16 degrees
Note: First one sprite then a large carrot sprite and finally some activity at lower altitude
1000 fps images covering the first sprite to the onset of the carrot sprite
(Left-right reversed. Sorry!)
AnimationAnimation
Leiden October 2007
Lightning
Lightning at USAFA
66,000 fps (15 μs)
Distance? (very close!!)
Field of view: 8x8 deg
Pix size: ~0.2 m (200 m range)
Thanks for your attention.