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Observations and statistics of small-scale streamer and bead features in sprites
Robert A. Marshall, Umran S. Inan
STAR Laboratory, Stanford University, Stanford, CA, USA
Contact: [email protected]
Workshop on “Streamers, sprites, leaders, lightning:
from micro- to macroscales”
Leiden University
10/10/2007
2
1. Background – Sprites
• Sprites occur at altitudes ~40 – 90 km (initiate at 75 km) following +CG discharges
• May be delayed from +CG up to ~200 ms• Manifestation of streamers and breakdown due to Quasi-electrostatic (QE) field
3
Background: Sprite formationF
rom P
asko, [1996]
4
Previous Sprite Observations
From Stanley et al, [1999]
From Stenbaek-Nielsen et al, [2000]
From
Gerken
et al, [2000]
5
Experiment Locations
Langmuir
Laboratory
(2004, 2005)
Yucca Ridge
Field Station
(2007)
Sept 30, 2007 0245 UT
6
2004 Experiment
• Equipment:– 16-inch Dobsonian (Newtonian) reflector– CCD chip with telescope yields 0.25 by 0.3
degree FOV– 500 km range - equivalent to 2.5 km.
10 m resolution in images– Kodak Ektapro Model 1012 Imager and Intensifier– 239x192 pixel array, in 12 blocks of 16 rows– 1000 fps at full resolution; higher speeds with
fewer horizontal scan lines– Spectral response ~ 440 – 700 nm (GenII
intensifier)
From Gerken et al, [2000]
7
Equipment Setup – 2004
8
Photometric measurements
• Wide-Angle Array for Sprite Photometry (WASP) is an array of six Hamamatsu photometers, arranged to yield a 6 x 16º FOV
• 25 kHz per channel sampling• WASP used to take measurements of sprite,
sprite halo, and/or elve intensity; later to be compared to early/fast VLF event data
• Camera used to co-align WASP field-of-view
From
Barrin
gton-L
eigh [2000]
9
Event 1: July 16, 2004, 5:32:33 UT
From
Gerken
and In
an [2004]
• In Gerken and Inan [2004], features appear to re-light pre-existing streamer channels
• In our work, such channels are not visible (below noise background?)
10
Event 3: Aug 09, 2004, 5:53:26 UT
From Gerken and Inan [2002]
From
Liu
and P
asko, [2004]
• In Gerken and Inan [2002], sharp tips appear to expand as they propagate downwards (?)
• In our work, a similar feature is observed, but propagation direction is ambiguous
11
Event 3: Aug 09, 2004, 5:53:26 UT
1
2
3
4
5
6
1 6
12
Event 4: August 22, 2004, 7:48:19 UT
• 2000 fps observation
• Propagation still not observable over the field-of-view imaged
• Observation yields a good measurement of the rise / fall of streamer brightness
Data is mean
along slice line
13
Event 5: August 12, 2004, 5:57:34 UT
• Most beads seen within sprite body; only a few rare cases apart from sprite body
• Movement?
14
August 9, 2004, 4:46:03 UT
1 ms frames2 ms integration
• Widths: ~ 30 – 150 m• Lifetime ~ 1.16 ms• Full brightness in < 250 ms
15
Bead Formations
• Sizes of ~10 m – 300 m
• Predominantly stationary, persisting for up to 10’s of ms
• Evolution is not well documented – appear in < 1 ms
• Size precludes measurement with photometers
From Gerken and Inan [2002]
16
Event 2: Aug 08, 2004, 5:18:13 UT
From Gerken and Inan [2002]
17
Bead and Streamer Statistics
• Streamer sizes from 10 – 300 m, in agreement with Gerken et al [2000], with most ~80 m
• Lifetimes NOT MORE than 6 ms in ANY cases
• Bead sizes also from 50 – 300 m, with a wider distribution
• Lifetimes up to ~10 ms (one outlier)
18
Streamer Sizes and Lifetimes v. Altitude
• Sizes do not show dependence on altitude
• Lifetimes show that at lower altitude, streamers persist for a minimum of time
From Gerken [2003]
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
19
Bead Sizes and Lifetimes v. Altitude
• Shows very little dependence on altitude for either sizes or lifetimes
– May be that both size and lifetime measurements fall under the noise level of the camera
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
20
More Recent Experiments: 2005
• RedLake HG-100k Camera (100,000 fps)– WASP photometer array– VLF recordings– 2 wide field-of-view cameras
• Weather was uncooperative
21
2007 Experiment
• Phantom 7.1 Camera (10,000 fps) borrowed from M. G. McHarg
• ITT Nightscope Intensifier (Gen III)
• Introduction of PIPER photometer array
• A few sprites seen in telescope at 100 fps, but when switched to higher speeds, weather became once again uncooperative
22
PIPER Introduction
• Photometric Imaging of Precipitation of Electron Radiation
• Array of 4 16-channel photometers with external amplification, power supply and filtering
• Cross-aligned photometers can yield image information at higher rate and sensitivity than any camera - continuously
MARCH 2006
MAY 2006MARCH 2007
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
23
Image Reconstruction
Orthogonal Photometers
Photometers
=1
82
12 14 13 11 16 14 14 13
11 20 19 21 26 20 18 20
13 19 24 44 53 42 35 28
14 20 30 43 55 50 43 32
17 18 25 43 50 48 45 35
17 20 26 41 49 48 42 40
16 18 25 35 36 36 33 34
13 14 20 24 25 24 23 24
Field of View
Photometer Data
=281
=107
=155
=258
=287
=283
=233
=167=1
13
=1
43
=2
62
=3
10
=2
82
=2
53
=2
26
24
PIPER Data Acquisition
PIPER
16 x 16 Photometer View
25
PIPER Data Acquisition
PIPER
16 x 16 Photometer View
26
PIPER Data Acquisition
PIPER
16 x 16 Photometer View
27
PIPER Data Acquisition
PIPER
16 x 16 Photometer View
28
PIPER Data Acquisition
PIPER
16 x 16 Photometer View
29
PIPER Data Acquisition
PIPER
16 x 16 Photometer View
30
PIPER Data Acquisition
PIPER
16 x 16 Photometer View
31
PIPER Data Acquisition
Integrated Camera Image
32
The Cube Interpretation
VerticalPhotometer
Data
HorizontalPhotometer
Data
CameraImage
TheDataCube
33
Reconstructing 2D Sprite Images
2 3 4 5 6 7Frame:C
amer
aF
ram
es
Hyp
.P
hot.
Fra
mes
By-
Han
dF
ram
esQ
PF
ram
es
34
Example PIPER data
• Sprite from July 10, 2007, 05:59:25 UT
• Image not yet reconstructed; data not yet calibrated
60 Hz
(in the noise)
35
Questions?
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.