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Transient Luminous Events (TLEs) and Early VLF events

Prepared by Robert Marshall, Benjamin Cotts, and Morris Cohen Stanford University, Stanford, CA IHY Workshop on Advancing VLF through the Global AWESOME Network. Transient Luminous Events (TLEs) and Early VLF events. The Most Famous TLEs: Sprites. Transient Luminous Events. Sprites.

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Transient Luminous Events (TLEs) and Early VLF events

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  1. Prepared by Robert Marshall, Benjamin Cotts, and Morris Cohen Stanford University, Stanford, CA IHY Workshop on Advancing VLF through the Global AWESOME Network Transient Luminous Events (TLEs) and Early VLF events

  2. The Most Famous TLEs: Sprites

  3. Transient Luminous Events

  4. Sprites

  5. Sprite Observing Equipment High-speed cameras Cummer et al [2006].

  6. Sprite Movie from Stenbaek-Nielsen, H. C., et al, (2007), GRL, 34, L11105

  7. Sprites and the Quasi-Electrostatic Field • Transient: endure <50 ms, usually 1–2 ms • Luminous: intense red emissions (>1 GR) • Observed by low-light CCD video cameras

  8. Sprites and the Quasi-Electrostatic Field • Transient: endure <50 ms, usually 1–2 ms • Luminous: intense red emissions (>1 GR) • Observed by low-light CCD video cameras

  9. Sprites and the Quasi-Electrostatic Field • Transient: endure <50 ms, usually 1–2 ms • Luminous: intense red emissions (>1 GR) • Observed by low-light CCD video cameras • Signature of quasi-electrostatic field

  10. Sprites and the Quasi-Electrostatic Field • Transient: endure <50 ms, usually 1–2 ms • Luminous: intense red emissions (>1 GR) • Observed by low-light CCD video cameras • Signature of quasi-electrostatic field

  11. Total Charge Moment + + • Total ELF energy is proportional to total charge transfer • ELF energy attenuates more in Earth-ionosphere waveguide + + + + + + + + + + + + + + - - - - - Total charge moment (I.e., C•km) + ELF Energy + Reising [1999]

  12. Sprite-producing sferics • Sprite producing sferics have strong ELF content • Evidence of long continuing currents in lightning • Nearly always has positive polarity Reising [1996]

  13. ELF and sprite intensities 13

  14. Elves • First observed in 1992 (Space shuttle) • Observed from ground by cameras and photometers after 1996 Space Shuttle 2003 Yoav Yair [2003] Elve ~90 km Cloud Top (~20 km) Modeling Optical Emissions Marshall [2009]

  15. Elves and the Lightning-EMP

  16. Elve Movie: Expanding EMP

  17. Peak Current + + + + • Peak current is proportional to VLF peak • Higher peak current  stronger EMP + + + + + + + + + + + + + + - - - - - - - - - - - - - Return stroke peak current (i.e., kA) + + + + VLF Peak + + + +

  18. Elve-producing sferics Barrington-Leigh and Inan [1999] • Elve-producing sferics have strong VLF content • Evidence of high peak current, strong EMP • Can result from either ‘+’ or ‘–’ polarity

  19. The Gigantic Jet Pasko et al. [2002]

  20. The Gigantic Jet From Pasko et al [2002]

  21. TLEs Observed from Space: ISUAL Sprites: 633, Gigantic Jets: 13 Elves: 5,434 Sprite halos: 657 From Chen et al, [2008]

  22. Introduction to Early VLF Events 22 22

  23. Early VLF Event Properties • Rapid onset delay (Dt < 20 ms) • Rapid onset duration (td < 20 ms) • Typically recover in ~30-200 s • Event amplitudes ~0.2-0.8 dB, rarely >1 dB • Forward scattering (< 30o) • Causative CGs <50 km from perturbed path • Lateral extent of disturbances ~100 km Source: [Johnson and Inan 2000]

  24. Early/fast Events in Broadband Data

  25. Sprites and Early VLF

  26. Early/fast Causative Mechanism Theories

  27. Recent Results in TLE Observations • Observations from Space aboard ROCSAT-2, and upcoming TARANIS • Chern et al [2003], Mende et al [2005], Frey et al [2005] • Lefeuvre et al [2006] (AGU Fall Meeting), Blanc et al [2007] (Adv. Space Res.)‏ • Correlations between sprites, early/fast, and sferic bursts • Ohkubo et al [2005], Van der Velde et al [2006], Marshall et al [2006,2007] • Sprites observed at 5,000 frames per second and higher • Cummer et al [2006], Nielsen et al [2007], McHarg et al [2007] • 3D Modeling of elves • Marshall et al [2008]

  28. Questions for Future TLE Research • Where else do sprites occur? Over what types of storms? To date, mostly over Mesoscale Convective Systems • Inexpensive ground-based cameras and photometers • How many elves occur compared to sprites? Over what storms? • Ground-based photometers and sensitive, triggered cameras • How many sprites have correlated early/fast events? What is the polarity of these events? What are the lightning signatures? • VLF receivers near sprite locations, preferably also near Lightning detection networks / VHF receiver networks • What types of storms produce Jets? Is Lightning correlated? Is there a VLF signature of Jets?

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