Transient Luminous Events (TLEs) and Early VLF events

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

The Most Famous TLEs: Sprites

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Transient Luminous Events

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Sprites

Sprite Observing Equipment

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

Sprite Movie

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

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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

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• Signature of quasi-electrostatic field

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• Signature of quasi-electrostatic field

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Total Charge Moment

Total ELF energy is proportional to total charge transfer

ELF energy attenuates more in Earth-ionosphere waveguide

ELF Energy

+ + ++ +

+ ++

++ +

+ + +++

--

---

+ +

Total charge moment (I.e., C•km)

Reising [1999]

Sprite-producing sferics

Reising [1996]

Sprite producing sferics have strong ELF content

Evidence of long continuing currents in lightning

Nearly always has positive polarity

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ELF and sprite intensities

Elves

• First observed in 1992 (Space shuttle)

• Observed from ground by cameras and photometers after 1996

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Space Shuttle 2003 Yoav Yair [2003]

Elve

~90 km

Cloud Top (~20 km)

Modeling Optical EmissionsMarshall [2009]

Elves and the Lightning-EMP

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Elve Movie: Expanding EMP

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Peak Current

+ + ++ +

++ ++

++ +

+ + ++++

- -- - -

- -- -

----

+ ++

++

+ +

+

Return stroke peak current (i.e., kA)

Peak current is proportional to VLF peak

Higher peak current stronger EMP

VLF Peak

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

The Gigantic Jet

19Pasko et al. [2002]

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The Gigantic Jet

From Pasko et al [2002]

TLEs Observed from Space: ISUAL

Sprites: 633, Gigantic Jets: 13 Elves: 5,434

Sprite halos: 657

From Chen et al, [2008]21

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Introduction to Early VLF Events

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Early VLF Event Properties

Rapid onset delay (t < 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]23

Early/fast Events in Broadband Data

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Sprites and Early VLF

Early/fast Causative Mechanism Theories

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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]

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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?

Documents

Transient Luminous Events (TLEs) and Early VLF events