Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz...

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Photograph by William Biscorn rld of TGFs Smith Department and Santa Cruz Institute for Particle Physics ty of California, Santa Cruz thanks to: Brian Grefenstette and Bryna Hazelton, UCSC Joseph Dwyer, Florida Institute of Techn

Transcript of Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz...

Page 1: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

The World of TGFs

David M. SmithPhysics Department and Santa Cruz Institute for Particle PhysicsUniversity of California, Santa Cruz

Special thanks to: Brian Grefenstette and Bryna Hazelton, UCSC Joseph Dwyer, Florida Institute of Technology

Page 2: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

Terrestrial gamma-ray flashes, relativisticrunaway, and high-energy radiation in theatmosphere

David M. SmithPhysics Department and Santa Cruz Institute for Particle PhysicsUniversity of California, Santa Cruz

Special thanks to: Brian Grefenstette and Bryna Hazelton, UCSC Joseph Dwyer, Florida Institute of Technology

Page 3: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

Mechanisms of air breakdown (decreasing E):

Cold runaway

Any e- goes relativistic

Conventional (Townsend) Ionization > attachment

Streamer

Self-propagating

Relativistic runaway

Rel. seed electron(s)

Leader

Thermal ionization Figure by V. Pasko, from tutorial at the

NATO summer institute on Sprites, etc.,

Corte, Corsica, 2004

Page 4: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

Graphic: Canadian Forest Service

+CG+IC

-CG

Types of lightning stroke:

Page 5: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

When/where might runaway occur relative to lightning?

Before (initiation) During (EMP/Elve) After (Sprite)

Page 6: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

How does lightning trigger?

M. Stolzenburg et al. , GEOPHYSICAL RESEARCH LETTERS, VOL. 34, L04804

Relativistic runaway?Streamers from enhanced fields near hydrometeors?

Page 7: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

Timeline of relativistic runaway• Wilson (1925) predicts runaway electronsWilson (1925) predicts runaway electrons

• Many observational attempts – mixed resultsMany observational attempts – mixed results

• Gurevich et al. (1992) predict runaway avalancheGurevich et al. (1992) predict runaway avalanche

• 1980's to today: modern observations from ground, 1980's to today: modern observations from ground, space, aircraft, balloons – bremsstrahlung means space, aircraft, balloons – bremsstrahlung means remote sensingremote sensing

• Dwyer (2003/2007/2008) Babich 2005: feedback Dwyer (2003/2007/2008) Babich 2005: feedback mechanismmechanism

counts w/ lightningcounts w/ lightningGeiger counters (10’s of km away)Geiger counters (10’s of km away)Schonland & Viljoen (1933)Schonland & Viljoen (1933)

counts, attributed to x-rays counts, attributed to x-rays from thunderstorms from thunderstorms

Dosimeters on 500m towerDosimeters on 500m towerWhitmire (1979)Whitmire (1979)

counts w/ T-stormscounts w/ T-stormsScintillation counter - mountain topScintillation counter - mountain topShaw (1967)Shaw (1967)

No lightning effectNo lightning effectGeiger counters (~2000 km away)Geiger counters (~2000 km away)Appleton & Bowen (1933)Appleton & Bowen (1933)

No high energy electronsNo high energy electronsPhotographic plates on balloonPhotographic plates on balloonMacky (1934)Macky (1934)

No high energy electronsNo high energy electronsIonization chamber under T-stormsIonization chamber under T-stormsSchonland (1930)Schonland (1930)

No high energy electronsNo high energy electronsee-- sensitive emulsions - 300m tower sensitive emulsions - 300m towerHill (1963)Hill (1963)

counts w/ T-stormscounts w/ T-stormsIonization chambers & countersIonization chambers & countersClay et al (1952)Clay et al (1952)

counts w/ lightningcounts w/ lightningCloud chamber synch. w/ lightningCloud chamber synch. w/ lightningHalliday (1934)Halliday (1934)

ResultResultExperimentExperimentPaperPaper

Thanks to B. Hazelton

Page 8: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

THREE Requirements for RR avalanche

Sufficient field (E > 2 kV/cm)

Sufficient potential drop (> 10s of MV)

Sufficient density for collisions giving

multiplication

Page 9: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

Positron & gamma-ray feedback

• Feedback limits the number of avalanche lengths possible;

• But feedback allows true discharge even with only a few avalanche lengths

• Feedback predicts correct TGF duration and approximate luminosity

• (Dwyer 2008)Plot courtesy of J. Dwyer

Page 10: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

Classes of high-energy observations

Surges – second-to-minute enhancements seen

from ground, balloons, aircraft – runaway without

breakdown?

Steps – microseconds, seen from ground in

stepped leaders – 10s of keV energy – cold runaway

in a small volume?

Terrestrial Gamma-ray Flashes – millisecond

duration, seen from space, ground – MeV energies –

true runaway breakdown?

Page 11: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

Observations of surges

Left: Eack et al. 1996, balloon; Right: McCarthy & Parks 1985, airplane

Surge enhancements often terminated or re-started by lightning

Page 12: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

New result: surges have RR spectrumFrom Tsuchiya et al. 2007, PRL – ground-based observation, winter thunderstorms

over Japan:

Page 13: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

Recent observations of steps

• Natural & rocket triggered lightning– Short bursts of x-rays during

the dart-leader or step-leader phase

– Energies up to ~250 keV– Cold runaway (E~Ec) in

leader tips?

J. R. Dywer et al, Science, 299, 694 (2003); J. R. Dwyer et al, Geophys. Res. Lett, 31, L01803 (2005)

Page 14: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

TGFs seen from the ground have RR

spectrumFrom natural lightning: Moore et al. 2001, GRL

From triggered lightning: Dwyer et al. 2004, GRL

Time history (left) and spectrum

(above) from Dwyer et al. 2004

Page 15: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

TGFs from space: BATSE and RHESSI:

1991-2000Large areaTrigger required76 TGFs in 9 years4 energy channels.Fishman et al. 1994,Science

2002-presentSmaller areaNo trigger needed> 800 TGFs in 6 yearsFine energy resol.Smith et al. 2005, Science

Page 16: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

From an accelerated electron to a count in your detector:

Ionization losses compete with acceleration; scattering broadens the electron beam

Bremsstrahlung softens photon spectrum relative to electron spectrum and gamma beam is broader than electron beam

Compton scattering of gammas in atmosphere softens and broadens the beam further – softer photons are delayed

Photoelectric absorption in atmosphere removes lowest-energy gammas

Compton and Photoelectric effects in spacecraft mimic atmospheric effects (except for delay)

Deadtime and pileup in detectors can further distort spectra

Page 17: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

Summed RHESSI TGFs have RR spectrum:

Flattening of spectrum @ 1 MeV requires production altitude 15-21 km: near tropical tropopause (just above thunderclouds)

Dwyer & Smith 2005Carlson, Lehtinen and Inan 2007

Page 18: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

Summed RHESSI TGFs have RR spectrum:

Depth also affects absorption at the lowest energies (harder to observe)

Spectrum is softer away from beam axis(Ostgaard et al. 2008)

Deep source implies much higher energies(can be hundreds of thousands vs. thousands of Joules)

See spectral modeling talks byB. HazeltonT. GjestelandN. OstgaardP. Connell

Page 19: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

RHESSI TGFs: Seasonal & diurnal dependence follows lightning

Page 20: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

Deficit at high latitudes relative to lightning, consistent with

production at tropopause (E. Williams et al. 2006, JGR)

?

=

Trop. vs.

latitude,

B.D. Santer

et al. 2002

Page 21: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

(Cummer et al. 2005, GRL; Inan et al. 2006, GRL)

What kind of lightning is associated with TGFs seen from space?

Use observations of ELF/VLF radio “atmospherics/sferics”

Statistical surveys: TGF sferics are present but weak

Single cases close-up: these are +IC strokes:

(Stanley et al. 2006, GRL)

Highest altitude

lightning – consistent

with tropopause

hypothesis – all

lightning may have

TGFs!

Page 22: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

(Cummer et al. 2005, GRL; Inan et al. 2006, GRL)

What kind of lightning is associated with TGFs seen from space?

Use observations of ELF/VLF radio “atmospherics/sferics”

Statistical surveys: TGF sferics are present but weak

Single cases close-up: these are +IC strokes:

(Stanley et al. 2006, GRL)

IS TGF CAUSE OR

EFFECT OF LIGHTNING?

Page 23: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

(Cummer et al. 2005, GRL; Inan et al. 2006, GRL)

What kind of lightning is associated with TGFs seen from space?

Use observations of ELF/VLF radio “atmospherics/sferics”

Statistical surveys: TGF sferics are present but weak

Single cases close-up: these are +IC strokes:

(Stanley et al. 2006, GRL)

IS TGF CAUSE OR

EFFECT OF LIGHTNING?

NEED BETTER THAN

RHESSI 2ms TIMING!

Page 24: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

Spectral evolution consistent with Comptonization

B. Grefenstette et al. 2008

Greater soft lags in BATSE data (Nemiroff et al. 1997 JGR;

Feng et al. 2002 GRL) are an instrumental deadtime effect

Page 25: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

Secondary electron beams MUST occur:

Page 26: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

Some BATSE events and one RHESSI event are clearly electron beams – but is the Compton mechanism adequate?

Page 27: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

Some BATSE events and one RHESSI event are clearly electron beams – but is the Compton mechanism adequate?

See talks by B. Grefenstette

B. Carlson

Page 28: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

Questions remaining:

Causality: (are TGFs a cause or effect of IC lightning?): need timing

Ubiquity: (do all types of lightning include TGFs?): need location

Relation to surges: need wide dynamic range & high sensitivity

Relation to optical phenomena (sprites, elves, etc):need common platform

Size, nature of avalanche region: need larger and more sensitive dataset with localizations

? Are the RHESSI

events the tip

of the iceberg?

Page 29: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

Because BATSE was more difficult to trigger, BATSE TGFs are

expected to be intrinsically brighter than RHESSI.

Page 30: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

Because BATSE was more difficult to trigger, BATSE TGFs are

expected to be intrinsically brighter than RHESSI.

The opposite is true.

BATSE is ~4x saturated

Page 31: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

A new result (which shouldn't be):

Most RHESSI TGFs count at maximum throughput

in the brightest 50 microseconds.

Stay tuned for statistical estimates of average saturation factor...

Page 32: Photograph by William Biscorner The World of TGFs David M. Smith Physics Department and Santa Cruz Institute for Particle Physics University of California,

Photograph by William Biscorner

Questions remaining:

How bright can TGFs really get?

Ask Sprite-SAT/ TARANIS/ ASIM...

?

?


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