Thunderstorm Ground Enhancements (TGEs)Natural accelerators in thunderclouds

A Workshop to promote Interdisciplinary Science at the Pierre Auger Observatory in Western Argentina

Ashot Chilingaryan, Alikhanyan National lab, former Yerevan Physics Institute

CRT Wilson: discovery of high-energy phenomena in atmosphere

“In a field of 20 kV/cm the energy supplied to -particle will exceed the average loss; so that particle will be continuously accelerated until some accident occurs” “There is, as well known, some evidence of the existence of penetrating radiation in the atmosphere; possibly some portion of it may originate in the electrical fields of thunderclouds.”

C. T. R. Wilson, the acceleration of -particle in strong electrical fields of thunderclouds, Proc. Cambridge Philos. Soc. 22, 534, (1925).E.R.Williams, Origin and context of C.R.T. Wilson’s ideas on electron runaway in thunderclouds, JGR, 115, A00E50, 2010.

Despite numerous negative results by Bazil Schonland, Edward Halliday and others in searching of energetic particles from thunderclouds (as a result of using inadequate equipment) Wilson supported the idea till his last publication in 1956.

Relativistic runaway electron avalanches (RREA)

Friction on electrons in air at sea level. Shown as a function of electron energy. The axis on the right indicates the electric field strength required to produce a force on an electron equal to the frictional force.

Brant Carlson’s PhD thesis

Terrestrial Gamma Flashes (TGFs)

A NASA space telescope hunting for the most powerful explosions in the universe is turning its eye on Earth to hunt for tiny flashes of radiation. Fermi Gamma-Ray Space Telescope has joined the search for TGFs above thunderstorms which are ultra-brief, but could be a concern for air travelers, 400 chest X-rays.

Thunderstorm Ground Enhancements TGEs- analogs of TGFs

• Despite the predictions of C.R.T. Wilson in 1924 the particle detection on the ground were rarely and not very credible;

• Japanese report 2 events with 20% enhancement with small NaI detectors; Baksan group 20 years measure the RREA, fluxes not very high due to bad site location; surface arrays EAS-top and Tibet report 10-20% enhancements of EAS triggers during thunderstorms; Lebedev inst. group on Tien-Schan’ are looking mostly for the evidence that EAS initiated lightning; Florida group measures X-rays initiated by artificial lightning.

• Small detectors, operating during short time detect only one component of secondary cosmic rays;

• Thunderclouds should be low and there are some additional, yet unknown conditions initiating the RREA and TGE.

Aragats Space Environmental Center (ASEC) research of the Solar Modulation effects at high and middle latitudes – to detect Ground Level Enhancements (GLE), Forbush

decreases, geomagnetic effects

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RREA Events – huge long lasting peaks in particle monitor time series (event library available)

Aragast Solar Neutron Telescope(“deep” calorimeter for 10-120 MeV particles)

100 – traversal of the low energy charged particle (~<200MeV);

010 – traversal of the neutral particle;

111 & 101 – traversal of the high energy muon (~>250MeV);

SEVAN basic unit: monitoring 3 species of secondary CR

Section of the Neutron Monitor

Cube gamma-electron Detector

STAND Detector

Boltek Storm Tracker PCI Lighting Detection system; measuring electrical and magnetic fields; 600km radius of detection and the bandwidth of the whole system is meant to be 40-400kHz. Distinguish4 types of lightning.

Boltec EMF 100 electrical mill; 20Hz frequency, up to 100 Kv/m electrical field strenght

Huge TGE of 19 September, 2009 detected by all monitors of the Aragats Space Environmental Center

TGE detected at 4 October, 2010

Outdoor and indoor stand alone scintillators detect huge peaks lasting tens of minutes – we name them Thunderstorm ground enhancements - TGEsMAKET – a surface array with 16 scintillators (1000 m.sq.) detect short coherent bursts of electrons (within 1 µsec);duration less than 50 µsec; small densities – can be easily distinguished from EAS events

A. Chilingarian, A.Daryan, K.Arakelyan, et al., Ground-based observations of thunderstorm-correlated fluxes of high-energy electrons, gamma rays, and neutrons, Phys.Rev. D., 82, 043009, 2010

2-way classification of the MAKET triggers – discovery of the short TGE events (particle

bursts of duration less than 50 µsec)

A.Chilingarian, et.al., Particle bursts from thunderclouds: Natural particle accelerators above our heads, Physical review D 83, 062001 (2011) 

Density spectra of 2 classes: Short TGE and EAS

Inverse problem solving: incident Gamma spectra recovery by the measured energy deposit spectra

Measured and simulated energy deposit spectra of Cube upper scintillator at 18:23, 4 October, 2010

The 200 trial spectra fitted by the second order polynomial (Cube detector data on 18:23, 4 October, 2010).

Energy Spectra of RREA gamma-rays: 19 September 2009, 4 October 2010

The mean TGE gamma-ray energies >10 MeV are 17 MeV and 18 MeV, the number of gamma-rays is ~100,000 and ~40,000 particles/sq.m.min., for the October 4 and September 19 events respectively. For the October 4 TGE, we have recovered the gamma-ray spectrum at energies 5-10 MeV by outdoor Cube detector. The spectrum is harder for low energy gammas -1.9±0.4 and the number of particles 5-10 MeV is 250,000 particles/sq.m.min. Agile :cumulative: -2.7; -0.5

Energy Spectra of RREA electrons on 19 September 2009

Thundercloud height ~ 130m, Multiplication rate – 2,000; ~ 8e-folding lengths; Total number of electrons ~ 3*10**11, Electrical field strength ~1.8 – 2.0 kV/cm

Origin of the peaks in the Neutron Monitor: photonuclear reaction? Additional negative muons?

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Origin of the peaks in the Neutron Monitor: photonuclear reaction?

Additional negative muons?• There is 14 significant NM peaks in 2009-2010;

• The correlation with gamma ray flux is poor; we cannot declare that RREA gammas are parents of all neutrons;

• If we take as seed particles not EAS electrons, but stepped leaders we have not enough gammas;

• The excess of the negative muons due to acceleration in the electrical field of the thundercloud cannot bridge the gap;

• At October 4 there were neutrons because the “bare” Bf3 proportional chamber demonstrates also peak at the same time.

• At the maximal minute 18:23, 4 October, 2010 we had 74 и 124 (normalized to 1 m2 )additional counts in bare tube and ANM correspondingly

Credit: T. C. Marshall, et al.,Observed electric fields associated with lightning initiation, GR,32, L03813, 2005

Series of balloons carrying electric field meters (and GPS) radiosondes were flown into thunderstorms.Three-dimensional maps of individual lightning flasheswere obtained with an LMA.The maximum measured E in the region was186 kV/m (130% Eth) at 5.77 km altitude. Volumewhere E exceeded the runaway threshold was estimated to be 1–4 sq.km, with a vertical depth of about 1000 m.When the measured Eexceeded Eth, lightning occurred within a few seconds and reduced the local E to less than Eth.

Model of TGF-TGE process

Temporal structure of the electrical field disturbances and

lightning

Necessary and sufficient conditions for TGEFirst negative, than posiive field (30 kV/m); -IC lightning

First positive, than negative field (30 kV/m); -IC lightning

Necessary and sufficient conditions for TGE

Large field – no TGE!

Considerably small field, no lightning – TGE!

Main Results• 2 types of Thunderstorm Ground Enhancements (TGE) process were detected:

short (< 50msec, seed – stepped leader) and long (tens of minutes , seed – EAS electrons);

• We prove that RREA can accelerate electrons up to 100 MeV and higher

• Simultaneously measured electron and gamma-ray energy spectra prove the correctness of the RREA theory of the high energy phenomena in the atmosphere. Spectral shape and the total number of the estimated RREA electrons, mean energies and multiplication rates are in overall agreement with theory of Wilson-Gurevich and simulations of Dwyer, Carlson and Babich. Derived elongation, height and strength of the electrical field are realistic and well agree with few experimental measurements (Marshall et al., 2005); RREA mechanism started at 5-6 km with detection of TGE at 3 km with electrical field strength 1.8-2 kV/m and seed particles both EAS electrons and stepped leaders can explain measured spectra.

• Large peaks detected by ANM good correlated with gamma-ray enhancement; at least part of neutrons born in the photonuclear reactions; however contribution of the enhanced flux of negative muons also may play role to the ANM peaks;

Further research• Necessary and sufficient conditions for TGE/TGF; • Seed particles for short and long TGEs;• PMT height spectra on the µsec scale;• The lightning enigma: physical model, connections

between lightning, TGE, TGF, RREA!• Another calibration of energy deposit by network of

NaI detectors;• Auger tanks can map the thundercloud with TGEs as

thundercloud will travel across the array!

TGE in Yerevan 12 April, 2011 at 800 m asl: on-line data from all ~ 200 channels of

the ASEC monitors is available from http://adei.crd.yerphi.am/adei/