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: 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 formation From Pasko, [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, UT

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 Barrington-Leigh [2000]

9 Event 1: July 16, 2004, 5:32:33 UT From Gerken and Inan [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 Pasko, [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

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 frames 2 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]

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

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

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 2006 MARCH 2007

23 Image Reconstruction Orthogonal Photometers Photometers = Field of View Photometer Data =281 =107 =155 =258 =287 =283 =233 =167 =113=143=262=310=282=253=226

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 Vertical Photometer Data Horizontal Photometer Data Camera Image The Data Cube

33 Reconstructing 2D Sprite Images Frame: Camera Frames Hyp. Phot. Frames By-Hand Frames QP Frames

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?