High-Energy Particle Showers in Coincidence with Downward Lightning - - PowerPoint PPT Presentation

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High-Energy Particle Showers in Coincidence with Downward Lightning Leaders at the Telescope Array Cosmic Ray Observatory John Belz University of Utah 35 th ICRC Busan, 20170714 Unknowns In Lightning Production When we consider how much

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High-Energy Particle Showers in Coincidence with Downward Lightning Leaders at the Telescope Array Cosmic Ray Observatory John Belz University of Utah 35th ICRC Busan, 20170714

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Unknowns In Lightning Production

“When we consider how much we know

about complex and exotic astrophysical

bjects half way across the universe, it is

quite amazing that we do not understand the basics of how something as common as lightning gets started in clouds just a few miles above our heads.”

– Dwyer & Uman, Physics Reports (2014)

Basic Problem: Measured fields

consistently too low by an order of magnitude.

Solutions

– Mismeasurement of field? – Initiation from water or ice particles? – Energetic runaway electrons?

~3 kV/cm

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Relativistic Runaway Electron Avalanche

In RREA regime: dT = dz(eE - Ff)

Requires ~MeV seed electrons
Present due to cosmic rays within

1 µsec in 100 m sphere at lightning initiation altitudes. (Carlson, 2008)

Basically always there!
Are rare effects (e.g. TGFs) due to

large RREA–seeding events?

E = 300 kV/m 1 seed electron @ 1 MeV ~2 km

GEANT4 Simulation

SLIDE 4

Terrestrial Gamma Flashes

Discovered with BATSE (CGRO)

1992

– Assumed to arise from sprites – Now known to be associated with

leader stage in intracloud discharges

RHESSI (>2002) 805 TGFs
Fermi Gamma Burst Monitor
AGILE
Duration: 100 µsec → 1 msec
Flux: 1014 → 1019 w/ E > 100 keV.

TGF Cartoon (W. Xu dissertation, 2015)

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Terrestrial Gamma Flashes

Discovered with BATSE (CGRO)

1992

– Assumed to arise from sprites – Now known to be associated with

leader stage in intracloud discharges

RHESSI (>2002) 805 TGFs
Fermi Gamma Burst Monitor
AGILE
Duration: 100 µsec → 1 msec
Flux: 1014 → 1019 w/ E > 100 keV.

RHESSI TGFs compared with RREA models. (Dwyer et al 2005)

Is there a downward counterpart to this phenomenon?

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TA Observation: “Burst” Events

Plot: T. Okuda

5 year data (2008-2013)
10 surface detector bursts seen

– 3 or more SD triggers,

∆t < 1 msec

– Occasional ∆t ~ 10 µsec

“Normal” SD trigger rate < 0.01 Hz.

These cannot be cosmic ray air showers.

Found to have close time/space

coincidence with U.S. National Lightning Detection Network (NLDN) activity.

Abbasi et al. Phys. Lett. A 381 (2017).

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TA/LMA (“Lightning Mapping Array”) Project:

R. Abbasi, J. Belz, M. Byrne, D. Ivanov, R. LeVon,
W. Hanlon, P. Krehbiel,T. Okuda, J. Remington, W. Rison,
D. Rodeheffer, H. Takai, R. Thomas, G. Thomson

and the Telescope Array Collaboration

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TA/LMA

10/2013 – Installation
10/2013-08/2015 – Unstable operation.
08/2015 – Visit, upgrade detector sites
08/2015-present – Optimal detector
04/2016 – Support awarded by US-NSF

Atmospheric and Geospace Sciences

W. Hanlon (UU), W. Rison (NMTech)

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How is Lightning Mapped?

Impulsive radiation VHF Receiver Fit to source x,y,z,t (offline) Combine to form map

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TA/LMA Event 20160510-024150

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TA/LMA Event 20160510-024150

Dashed lines: TASD triggers

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20150915-12:13:04 20150915-19:37:01

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The “Slow Antenna”

GPS-timed capacitor,

read out with 4 s time constant.

Record changes in

electric field

vs Electric Field Mill;

measurements of DC Field

Active element; RC ~ 4 seconds

J. Remington and R. Abbasi (UU)

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SD Trigger Burst 20140905

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SD Trigger Burst 20140905

(first discharge)

Stepped-leader field change Return stroke field change

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SD Trigger Burst 20140905

(first discharge)

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Are we seeing downward TGFs?

GEANT4 simulation TASD: exploded view Cosmic ray core waveform Cosmic ray core waveform Leader-coincident core waveform

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Are we seeing downward TGFs?

Photon absorption length

plateaus at few 10's g/cm2 above ~100 keV.

∼100's of meters @ TA elevations
Few of the primary photons make

it to the ground!

pdg.lbl.gov

Simulation study: TASD

response to RREA-Photon Spectrum at Altitude

“Consistent” (term used

loosely) with TA observations

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Are we seeing downward TGFs?

Overall duration of SD

bursts comparable to

bserved TGF ∆t
Discrete subevents

from few to few 10's of µsec.

More to be studied

here!

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Summary

TA/LMA in full operation since August 2015.
Multiple events recorded in which TASD “trigger bursts”

are coincident with LMA or slow antenna activity.

Events consistent with downward

Terrestrial Gamma Flashes.

A significant role for cosmic

ray detectors in this field!

Paper submitted to Geophysical Research Letters;

arXiv:1705.06258

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Backup

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SD “Trigger Bursts”, 2015-2016

Okuda criteria; 16 µs < ∆t < 1 ms
3 bursts found:

– 20150915, 12:13:04, VEM = 30, 449, 37, 142, 39 – 20150915, 19:37:01, VEM = 72, 75, 47, 25 – 20160510, 02:41:50, VEM = 105, 109, 4,162, 22,118*

Full LMA and NLDN information...

* saturated FADC

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Downward Leaders Followed by Cloud-to-Ground Stroke

“Leaders” precede main flash.
Responsible for current-

carrying channel which is followed by flash.

High potential gradients in

upward leaders responsible for Terrestrial Gamma Flashes (TGFs)

http://www.lightningsafety.noaa.gov/

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Downward Leaders Followed by Cloud-to-Ground Stroke

“Leaders” precede main flash.
Responsible for current-

carrying channel which is followed by flash.

High potential gradients in

upward leaders responsible for Terrestrial Gamma Flashes (TGFs)

http://www.lightningsafety.noaa.gov/

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TA/LMA Event 20150915-121304

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TA/LMA Event 20150915-121304

Dashed lines: TASD triggers

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TA/LMA Event 20150915-193701

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TA/LMA Event 20150915-193701

Dashed lines: TASD triggers

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SD Trigger Burst 20140905

(second discharge)

Dart-leader and second return stroke