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

1. 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: ram80@stanford.edu 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 Gerken et al, [2000] From Stenbaek-Nielsen et al, [2000]

5. Experiment Locations Yucca Ridge Field Station (2007) Langmuir Laboratory (2004, 2005) Sept 30, 2007 0245 UT

6. From Gerken et al, [2000] 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)

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 • 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?) From Gerken and Inan [2004]

10. Event 3: Aug 09, 2004, 5:53:26 UT 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 From Gerken and Inan [2002]

11. 1 2 3 4 5 6 1 6 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

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 MARCH 2007 MAY 2006

23. Field of View =107 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 =155 =258 =287 =281 =283 =233 =167 Image Reconstruction Orthogonal Photometers Photometers =113 =143 =182 =262 =310 =282 =253 =226 Photometer Data

24. PIPER PIPER Data Acquisition 16 x 16 Photometer View

25. PIPER PIPER Data Acquisition 16 x 16 Photometer View

26. PIPER PIPER Data Acquisition 16 x 16 Photometer View

27. PIPER PIPER Data Acquisition 16 x 16 Photometer View

28. PIPER PIPER Data Acquisition 16 x 16 Photometer View

29. PIPER PIPER Data Acquisition 16 x 16 Photometer View

30. PIPER PIPER Data Acquisition 16 x 16 Photometer View

31. PIPER Data Acquisition Integrated Camera Image

32. The Cube Interpretation Camera Image Horizontal Photometer Data The Data Cube Vertical Photometer Data

33. Reconstructing 2D Sprite Images Frame: 2 3 4 5 6 7 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?