Multi-point radiation measurements
for gamma-rays from accelerated electronsin winter thunderstorm
雷雲ガンマ線の多地点観測プロジェクトが拓く新展開
Teruaki Enoto (#1), Yuuki Wada, Yoshihiro Furuta, Takayuki Yuasa,Kazuhiro Nakazawa, Toshio Nakano, Harufumi Tscuhiya,
Masashi Kamogawa, Daisuke Yonetoku, Tatsuya Sawano
and on behalf of the GROWTH collaboration#1: Department of Astronomy and Hakubi Center, Kyoto University

see also talk by Wada @MIS18-05, 5/22 (today) 11:45 AM-12:00 PMJpGU-AGU Joint session M-IS05 (Thunderstorm and Lightning) @ Chiba, Japan, 2017/05/22 (15 min)http://pcwallart.com/image-post/183236-thunderstorm-wallpaper-1.jpg.html

じめとする光子が放射され、地上からも観測の可能性がある。世界的に見てもエネルギーが高い冬季雷が発生する日本海側において、このような現象の探索し詳細な解析を行いうる検出器を設置し、観測を開始
Electron
Acceleration in Electric Fields
することが本論文の目的である。
acceleration is usually difficult under• Electron
宇宙物理学の観点から本テーマを見たキーワードが粒子加速であdenseatmosphere (short range of electrons).
るのに対し、地球理学的な視点から見れば、地球上で毎秒100 回生

じていながら未だよくわかっていない落雷のメカニズムに迫ると言High
energy radiation measurements from•••••える。例えば、空気中で絶縁破壊を起こすことのできる電場強度はthunderstorms(MacCarthy et al., 1985; Eack et al., 1996)
3 MV/mであるのに対し、実際に雷雲内で観測される電場強度は一naturallightnings(Moore et al., 2001)
桁ほど小さい 0.2 lightnings
MV/m でしかない。この結果は、雷雲中の強い電rocket-triggered(Dwyer et al, 2003)
場による逃走電子のなだれ的な再生産をモデルに組み込むことで解Terrestrial
Gamma-ray Flashes (TGFs) in a low-Earth orbit
fromsatellites (Fishman et al, 1998; Smith et al., 2004)
消される可能性がある。また、落雷の際にリーダとよばれる不連続で階段状に伸びる導電路の形成過程も具体的な仕組みは未だ謎のまacceleration of electrons by electric• Relativisticまである。

fields both in thunderstorms and lightnings?

このような展開の中で、90 年代に入って雷雲上空のスプライト/エルブスといった発光現象の研究が進み、アメリカではロケット誘雷
high energy radiation enhancements• Prolongedを用いてガンマ線のスペクトルを調べる試みが始まっている[Dwyerdetectedfor a few minutes from Japanese winterthunderstorms(Yamasaki et al., 1998;
Torii γet線による観測は、al., 2002)
et al., 2003]。一方、日本海側の冬季雷のX 線やDwyer et al., 2003, Science
図 1.2: フロリダの誘未だに解明されない点が多いにも関わらず研究の余地が多い、ニッ
雷実験 [Dwyer et al.,
チな研究テーマと言える。本研究は、雷という地球物理学的な現象
Question:Radiation mechanism, event rate, and atmospheric
2003]。 condition?
を用い、粒子加速という物理学の研究を行うもので、さらに遠隔デー

Observation of Winter Thundercloud (GROWTH) project
タ取得や自律システムの構築など、宇宙実験の手法を活用できるという独創的なテーマである。
• Gamma-Ray

since22006(Tsuchiya, Enoto et al., 2007 PRL, 2009 PRL,
2011
JGRD, and 2013 PRL).
章では雷雲や雷の諸現象の物理をまとめ、現在進行中のX線/γ 線の観測例を述べるとともに、電場による相対論的粒子の加速機構の理論についても触れる。3 章では、日本海側での実際の観測事例から想・20日、宮崎県の路上で落雷事故。

㻝᪥㻔Ỉ㻕෤ᆺ䛻⛣⾜㻞᪥㻔ᮌ㻕෤ᆺ䛾Ẽᅽ㓄⨨ᙉ䜎䜛

北日本を低気圧が急速に発達して通過し 全国的に風強く北陸～北日本日本海側で冬型の気圧配置へ。東～北日本や西日本 は大雪でふぶく。福島県桧枝岐で日降雪
日本海側で雪や雨。全国的に風が強まり 量 㻣㻜㼏㼙 、 山 形 県 飛 島 で 最 大 瞬 間 風 速
北海道えりも岬で最大瞬間風速㻟㻞㻚㻡㼙㻛㼟。 㻟㻜㻚㻣㼙㻛㼟。北海道全てを含む㻞㻥㻠地点で真宮崎市でウメ開花。
冬日。水戸市でウメ開花。

1414第2章
WinterThunderstorms
along the Japan Sea
Periodic wind from the northeast, originating from the Siberian cold front,
provide a rare environment for thunderstorm swith high energy phenomena.
(Rakov and Uman, 2003)

2017/2/6 15:00 JST
Himawari-8 Real-time Web / NICT
http://himawari8.nict.go.jp

Height (km)16windFlorida
Summer12
8mountains 㻡᪥㻔᪥㻕㻞䛴䛾పẼᅽ䛻䜘䜛㞵㻟᪥㻔㔠㻕す᪥ᮏ䛷䛿෤ᆺ⦆䜐㻠᪥㻔ᅵ㻕✜䜔䛛䛺❧᫓

西～東日本は日本海側など一部を除き晴れ、近畿以北の日本海側は雨や雪。最高気温は平年より㻠䉝以上高い所も。徳島市でウメ開花。熊谷市では平年より㻝㻢日早くヒバリ初鳴。

日本付近は移動性高気圧に覆われ、概ね晴れて穏やかな天気。九州では夜遅くかKashiwasaki
ら雨。全国的に気温高く、最高気温は北海道を除く地点のほとんどが㻟月上・中旬並。

JapanWinter

4

前線を伴った低気圧が本州付近を東進し、九州中心に西～東日本は広範囲で雨。夜は別の低気圧が発達しながら日本海を東0進し、東北でも雨や雪。長崎県福江で㻟㻢㼙㼙㻛㻝㼔。

UniqueJapanese
winter thunderstorm:
図 2.13properties
雷雲の典型的な高度
図of2.13雷雲の典型的な高度[Rakovand Uman,[Rakov200• low altitude (sometimes <1 km),• powerful (x101-3) and frequent lightnings,• higher rate of positive discharges (~33%),• and sprite & elves above the sea.

Understrongthunderstorms,
we have been
detected
えば 1997 年 1えば月 291997
日の観測例では、構内の年1月29 日の観測例では、構内の5 基、構外の15基の計基、構外の6基>20 gamma-ray events for 10 years at Kashiwasaki.

おいて、NaI 検出器や熱ルミネセンス線量計
おいて、NaI• 検出器や熱ルミネセンス線量計(TLD)の指示値上昇が上昇が(TLD)meterの指示値
10 MeV gamma-ray range
is several
hundred2017/2/6 09:00 JST,Japan Meteorological Agency

on ground (a several dozen m of 10 MeV electron).

も電磁的ノイズを受けにくく、設置場所による上昇開始のずれも見つかっても電磁的ノイズを受けにくく、設置場所による上昇開始のずれ

Observation Sites of the GROWTH ProjectWe started a new multi-point mapping observation since 2015 to increase
the sample of the high energy events and to trace moving thunderstorms.
Kashiwasaki Site

Winter Sites (Number of monitoring points)

a: Environmental control build.
b: Main building
c: Weather observation stationd: Radiation monitor 6

Summer Sites
InstitutesSuzu
4~ 1 km

Kashiwasaki
abKomatsu

3cKanazawa

d2

RIKEN
Mt Norikura
Univ. of Tokyo
Mt Fuji

Komatsu Site
e: Komatsu high schoolf. Science Hills Komatsu~3 kmefKyoto Univ.

We installed 10 detectors in 4 areas in FY2016 winter. They are on the roofof local high schools and a science museum with getting cooperation fromteachers and museum staffs to cover a wide area away from the coast.
imagery@2017 CNES/Airbus, DigitalGlobe, Landsat/Copernicus, Map data @ 2017 Google, ZENRIN

Our winter observations have been supported by Kashiwazaki-Kariwa power station & TEPCO, Inc., Kanazawa University,Kanazawa University Senior High School, Izumigaoka High School, Ishikawa Komatsu High School, and Science Hills Komatsu

Low-cost DAQ System Controlled by RaspPiBoardWe newly develop a “stand-alone” & “low cost” data acquisition system (DAQ)
with two electronics boards (Front-end & ADC) controlled by Raspberry Pi3.

data acquisitiondADC board• Gamma-rays detected with BGO scintillators• Each photons recorded with energy and time
• GPS time tag, and on-board display of DAQ• Environmental sensors (temperature, pressure, etc)
• Mobile data transfer & remote control
Real-time monitoring of the website
95 mm •DC 4
ht and detection timeth FPGAquisition withRaspberry Pill-sized linux)
ion possible
95 mmW
95,000JPY (~$1k)(Shimafuji Elec.)
Yuasa & Shimafuji Elec.

(ref) FPGA/ADC board specification (50 MHz x 12 bit, 4 ch ADC)
http://ytkyk.info/blog/2016/09/04/growth-fpga-adc-board/ (C) T. Yuasa

Front-end
Board
BGO scintillator

web camera(25x8x2.5 cm3)

PMT
DAQelectronics

cm

20 cm

ADC board

45c35mRaspberry Pi

DAQ

water proof box(Detector FY2016)

Wada, Master thesis of the University of Tokyo, “Construction of the multi-point observation network for thundercloud gamma-rays”
MIS18-05
See the talk by Wada @ MIS18-05 at this JpGU, 5/22 (today) 11:45 AM - 12:00 PM for details

Low-cost DAQ System Controlled by RaspPi

Board

data acquisition

Cost >$20 k

Cost ~$4 kdDC 4ht and detection timeth FPGAquisition withll-sized linux)
ion possible
W
2006 December
Yuasa & Shimafuji Elec.

2016 October

Front-end
Board
BGO scintillator

web camera(25x8x2.5 cm3)

PMTDAQ
electronics

cm

20 cm

ADC board

45c35mRaspberry Pi

DAQ

water proof box(Detector FY2016)

Wada, Master thesis of the University of Tokyo, “Construction of the multi-point observation network for thundercloud gamma-rays”
MIS18-05
See the talk by Wada @ MIS18-05 at this JpGU, 5/22 (today) 11:45 AM - 12:00 PM for details

Academic Crowdfunding
学術系クラウドファンディングサイト academist (アカデミスト)

Original Return (Reward)
designed by Adachi design Lab.

Mug
Original T-shirt

日本海沿岸に住んでいたことがあり、冬季の雷を思い出しました。とても興味深い研究だと思います、応援しています。
Acknowledgement & USB

お二人のプロジェクトを見て、久しぶりにとてもわくわく
At the initial phase of our project, citizen supporters financially helped us through the academic
しました！今はささやかな資金貢献しか出来ませんが、私crowdfunding. The donation gathered during the two month was ~$16k from 153 contributors. Thishas been used for prototype manufactures and preparing for power-plugs on the high school roofs.
もいつか、自分の専門分野を通じて科学技術に貢献できるよう仕事頑張ろうと思いました。がんばってください！！
Thank you for your support : )Since 2015, our project has been supported by the crowd funding “academist”, Grants-in-Aid for Young Scientists (A) Kakenhi
16H06006, the SPIRITS program of Kyoto University, and the joint research program of the ICRR, University of Tokyo.

CoLongburst
atScienceHills
Komatsu
1015

Gamma-rays
Detectedfrom
Thunderstorms
・Extract Subtracted
spectrum fromSource(150 sec) and105

345

102Countrate-1 (cnt/s)
Counts
MeV-1
Count Rates(count/sec)

4040

35-1

Count s MeV-11010
3030

40K> 3 MeV~15000 photons detectedgamma-rays(0.8-14.0 MeV)

from thunderstorms
208Tl

25 1

2020
10 minute101510-1
Sourcecosmic-ray induced
background101010 Background5
Subtracted
0100-302:30 1 02:40 02:50 03:00 03:10 03:20 10
1003:00
03:20
10102:40 2 Date
(JST)(MeV) 5
EnergyEnergy(MeV)Time(JST)5050−1−2−311Flux = 0.65 ± 0.05 cm-2 s-1(0.04-10 MeV)

1010-1−1

Photons cm-2 s-1 MeV-1

35010
1050

Photons cm-2 s-1 MeV-1

Background(30minin gamma-rays
total).
0
Example:Prolonged(~2min)detected
on2016
December
8,
0
02:30
02:40
02:50
03:00
03:10
03:20
003:2002:40
Date03:00
(JST)
・Fit
response-resolved
spectrum.
~3:00
(JST)
at Science Hills Komatsu
as a dense cloud passing the above.

1010-2−2

Gamma-ray spectrum(background-subtracted,detectors response corrected)

1010-3 Oneluminous
eventsF(E)=E-Γofexp(-E/Ecut)−3Total detected photon ~3,400 cat

in GROWTH Experiment.
Γ=0.31, Ecut=3.6 MeV,
Fx=0.65 cm-2 s-1 (0.04-10 MeV)

1010-4−4112 Energy (MeV) 5
Energy (MeV)

1010Wedetecteda winter
longburst
event at
ScienceHills
KomatsuGamma-rays
fromthunderstorms
extenduptoatleast~10 MeV.
40
consisting of gamma-ray continuum exceeding 10 MeV.
4540

Count Rate (count/sec)

duration (~2bremsstrahlung
minute) is consistent
the speed ofelectrons.
a moving cloud.
•30Prolonged
Originatingofwith
accelerated
Also detected at another point with a time lag → Quasi-static electron acceleration•22 May2017
JpGU+AGU Joint Meeting 2017 大気電気学 MIS18-05•20Cutoff power-law spectrum → Consistent with the electron Bremsstrahlung emission
3530

2520

151010

Talk by Wada @MIS18-05, 5/22 (today) 11:45 AM-12:00 PM

Thunderstorms as a Natural Accelerator
1. Cosmic rays knock out
high energy seed electrons(e.g., >100 keV).

Radiations before
lightnings?

2. Strong electric fields
generate the relativistic
runaway electron
avalanche (RREA).

Cosmic rays
+ charge+−- charge −StrongElectricField(Pocket plus charges)

Bremss.
Gamma-rays+−

Electron acceleratione++−−e+ charge+e

Multiplicatione ee e+++LightningDischarges

3. Runaway electrons emit
bremsstrahlung gammarays when interacted withthe atmosphere.
4. Accelerated electrons
generate an ionised path ofdischarge (steppedleader)?
5. As the leader reaches theground, a huge current run
the path (return stroke).

Tsuchiya, Enoto, et al., PRL 2007, 2009
榎戸, 修論「雷雲電場による粒子加速の観測的研究」東大 (2007)
榎戸&土屋「雷雲は天然の粒子加速器か？」天文月報 (2008)

Relativistic Runaway Electron Avalanche
Dec.

Dec.

Acc.

izaIon

10Edstandard
atmosphereem

EbBr

Breakdown E-ﬁeld Eb (~2-3 MV/m@1atm)

ss.

ntio

Energy loss (MeV/m)

All electrons run away

1
Electric field E (e.g., 0.3 MV/m)
Observed

0.1

10-4

Maximum
Energy10-2

Maximum energy (~10 MeV)
is consistent with our observation

1102

Electron Kinetic Energy (MeV)(Gurevich et al., Phys. Lett. A, 165, 463, 1992)

Gamma-rays Associated with Lightnings
Counts/binSpiky radiations (<0.1 s) detected coincidence with lightning discharges.
(Example) 2017 February 6, 17:34 JST at theKashiwasaki siteLightCurve : 20170206_170753.fits (ch0, E>1 MeV, Bin Time = 0.05 sec)
450

Bin time = 50 msec
E > 1 MeV

400
350
300
250
200
150
100
50
0
−4−202462017年2月6日
17:34:05(JST)からの時間(sec)
Time(s) since2017 Feb. 6 , 17:34• Similar spiky event was previously detected
on 2012 January 13 (Umemoto et al., 2016)• A positron-electron annihilation line at 511 keV
was detected during the mysterious 2012 event.

We have detected 12 radiation events (including two short spiky events) inFY2016, already amounting to 32% of the total events since 2006.

Future Plan of Our GROWTH Collaboration
Our group is building a new multi-point observation network along the Japansea based on radiation measurement techniques of the X-ray astronomy.
Observation will be compared with numerical simulation of thunderstorms• Yousuke Sato (RIKEN/AICS→NagoyaUniv.) has implemented lightnings tometeorological simulation library SCALE(Scalable Computing for Advanced Libraryand Environment) for thunderstorms.
• We also developed Geant4 Monte Carlosimulation of gamma-ray propagation in
the atmosphere (lead by Y. Furuta).
• The number of observation site will
increase in FY2017 (at least additional 3).
• Electric field monitoring will be added via
our interdisciplinary collaboration.

We will tackle to resolve the condition of
the electron acceleration in Japanese
winter thunderstorms.

mk
40

white: water
red:plus charge
blue: negative charge
yellow: lightning
80 gird (500 m scale)(C)RIKEN AICS/Y. Sato

Summary
1. Strong and low-altitude winter thunderstorms along the Japan sea
provide a unique opportunity to directly detect Bremsstrahlung
gamma-rays from relativistic electrons accelerated in electric fields.
2. We developed a new portable, stand-alone, and low-cost gamma-ray
detector and installed 10 observation points in 4 areas along theJapan Sea to trace moving thunderstorms.
3. We successfully detected 12 radiation during FY2016 winter including
10 prolonged gamma-ray events from thunderstorms and 2 short spiky
events associated with lightning discharges.
see also talk by Wada @MIS18-05, 5/22 (today) 11:45 AM-12:00 PMWe are planning a workshop in Japan for the highenergy atmospheric physics (support by ICRR).
We welcome domestic and international
collaborations for winter thunderstorm observations.