Observations and statistics of small-scale streamer and bead features in sprites

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

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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]

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Experiment Locations

Langmuir

Laboratory

(2004, 2005)

Yucca Ridge

Field Station

(2007)

Sept 30, 2007 0245 UT

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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]

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Equipment Setup – 2004

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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]

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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?)

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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

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Event 3: Aug 09, 2004, 5:53:26 UT

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2

3

4

5

6

1 6

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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

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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?

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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

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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


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Event 2: Aug 08, 2004, 5:18:13 UT


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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)

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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.

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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



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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

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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

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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



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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

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PIPER Data Acquisition

PIPER

16 x 16 Photometer View

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PIPER


26


PIPER


27


PIPER


28


PIPER


29


PIPER


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PIPER


31


Integrated Camera Image

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The Cube Interpretation

VerticalPhotometer

Data

HorizontalPhotometer

Data

CameraImage

TheDataCube

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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

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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)

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Questions?



Documents

Observations and statistics of small-scale streamer and bead features in sprites