Progress in Earth andPlanetary Science

Wada et al.
Progress in Earth and Planetary Science(2023) 10:6
https://doi.org/10.1186/s40645-023-00538-2

Open Access

RESEARCH ARTICLE

Synoptic meteorological conditionsof gamma‑ray glows in winter thunderstorms
Yuuki Wada1,2* , Miwa Tsurumi2,3, Syugo Hayashi4   and Koichiro Michimoto5

Abstract
The Gamma-ray Observation of Winter Thunderclouds collaboration has detected 70 gamma-ray glows, a highenergy phenomenon associated with thunderstorms, from October 2016 to March 2020 in Kanazawa and Komatsu,
Ishikawa Prefecture, a central part of Japan facing the Sea of Japan. Based on surface and 500 hPa analyses, numericalprediction models, and surface and satellite observations, we classify their synoptic meteorological conditions into
mainly three types. Most of the glow-detection cases were in west or west-southwest winds around the detection
sites. Over half of the cases took place when a convex structure of surface pressure, often associated with a troughat 500 hPa, was formed along the coast of the Sea of Japan. Besides, we extract non-detection cases during winterthunderstorms in Kanazawa to compare with the glow-detection cases. While some of the non-detection cases have
similar meteorological conditions as the glow-detection cases, most of the non-detection cases exhibited higher
temperatures at the surface and 850 hPa, and higher − 10 ◦C altitudes, which indicates that electrification occurs at
higher altitudes than the glow-detection cases. Therefore, gamma rays might have been produced but were attenuated before reaching the ground and undetectable at sea level.
Keywords Gamma-ray glow, Winter thunderstorm, High-energy atmospheric physics, Lightning discharge,
Thundercloud
1 Introduction
Gamma-ray glows (also referred to as long bursts andthunderstorm ground enhancements: TGEs) are highenergy phenomena associated with thunderstorm activities. Gamma-ray glows are thought to originate from
relativistic electrons inside thunderclouds. In strong*Correspondence:
Yuuki Wada
wada@yuuki-wd.space
1
Graduate School of Engineering, Osaka University, 2‑1 Yamadaoka, Suita,
Osaka 565‑0871, Japan
2
Extreme Natural Phenomena RIKEN Hakubi Research Team, Clusterof Pioneering Research, RIKEN, 2‑1 Hirosawa, Wako, Saitama 351‑0198,
Japan
3
Graduate School of Science and Engineering, Aoyama Gakuin University,
5‑10‑1 Fuchinobe, Sagamihara, Kanagawa 252‑5258, Japan
4
Meteorological Research Institute, Japan Meteorological Agency, 1‑1
Nagamine, Tsukuba, Ibaraki 305‑0052, Japan
5
Independent Scholar, 2‑44‑11 Kosenba‑machi, Kawagoe, Saitama
350‑0036, Japan

electric fields of thunderclouds, electrons are accelerated by a scheme such as relativistic runaway electron
avalanche (RREA: Gurevich et al. 1992) and modificationof the cosmic-ray spectrum (MOS: Chilingarian et al.
2014) and emit bremsstrahlung photons by colliding
with atmospheric atoms. While the first detections weremade by airborne experiments (Parks et al. 1981; McCarthy and Parks 1985), most of the gamma-ray glows weredetected by high-altitude ground-based experiments at
Mt. Aragats in Armenia (Chilingarian et al. 2010, 2017,2019), in Yangbajing in Tibet, China (Tsuchiya et al.
2012), at Tien Shan in Kazakhstan (Shepetov et al. 2021),
in Puebla, Mexico (Bowers et al. 2019), at Lomnicky Stitin Slovak Republic (Chum et al. 2020), at Musala in Bulgaria (Chilingarian et al. 2021), at Mt. Norikura (Tsuchiya
et al. 2009) and Mt. Fuji (Torii et al. 2009) in Japan.
Gamma-ray glows have been also detected at sea level
during winter thunderstorms in Japan (Torii et al. 2002;
Tsuchiya et al. 2007; Kuroda et al. 2016; Wada et al.

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Wada et al. Progress in Earth and Planetary Science(2023) 10:6

2021a). Cold and dry air masses from Siberia are provided water vapor when crossing the Tsushima warm
current, and then convective clouds with lightning discharges are produced and approach the coastal area of
the Sea of Japan (Ishii et al. 2014). In general, gamma-ray
photons are attenuated in the atmosphere within several
hundreds of meters. For example, the average photon
energy of gamma-ray glows is 2–3 MeV as derived withan average energy spectrum (Wada et al. 2021a), and themean free path of 3 MeV photons is 220 m at sea-level.
Therefore, gamma rays produced in summer thunderstorms hardly reach the ground because their charge
center is typically above 3 km. To avoid the attenuationof gamma rays in the atmosphere, airborne experimentswith aircrafts and balloons or ground-based observations
at high altitudes are necessary for summertime thunderstorms. On the other hand, gamma-ray glows in winterthunderstorms can be detected even at sea-level because
their charge center and the lower charge-layer edge canbe at 1–2 km and at < 1 km, respectively, resulting in lessattenuation of gamma rays in the atmosphere. The firstdetection in a winter thunderstorm was made by radiation monitors around the Monju Nuclear Power Plant,
Fukui Prefecture (Torii et al. 2002). The Gamma-ray
Observation of Winter Thunderclouds (GROWTH) collaboration started a dedicated gamma-ray observation at
the Kashiwazaki-Kariwa nuclear power station, Niigata
Prefecture (Tsuchiya et al. 2007, 2011, 2013), and then is
operating an observation network with multiple gammaray monitors in Ishikawa Prefecture (Wada et al. 2018,2019, 2021b; Yuasa et al. 2020). A total of 70 gamma-ray
glows were detected in Ishikawa in four winter seasons
from October 2016 to March 2020 (Wada et al. 2021a).
Winter thunderstorms have characteristics quite different from summer ones (Kitagawa and Michimoto
1994; Rakov and Uman 2003). (1) Charge center is frequently at 1–2 km, and the lower charge-layer edge canbe at < 1 km. Thunderclouds in wintertime have a lower
charge center because the altitude of − 10 ◦C where
the charge-separation process is thought to efficiently
work gets closer to the ground (Kitagawa 1992; Kitagawa and Michimoto 1994; Yoshida et al. 2008; Takahashi et al. 2019). (2) Lightning discharges that release
more than 100 C are occasionally observed (Brook et al.
1982; Suzuki 1992). (3) The ratio of positive cloud-toground discharges to negative ones is higher than insummertime (Takeuti et al. 1978; Brook et al. 1982;
Ishii et al. 2014). (4) Lightning discharges are frequently
initiated by upward leaders from tall ground objects(Miyake et al. 1990; Suzuki 1992). (5) The duration ofthunderstorm activities is generally shorter and lightning flashes are less frequent than in the summertime.
In particular, thunderstorms that exhibit only a few

Page 2 of 21

lightning flashes in their lifecycle are called “single-flash
storms” (Michimoto 1993). Michimoto (1993) concluded that single-flash storms likely develop when the− 10 ◦C altitude is between 1.4 and 1.8 km. The singleflash storms could be important for gamma-ray glows
because they occur in the lower charge-center condition, and also quasi-stable electric fields that accelerate
electrons are not interrupted frequently.
Synoptic conditions of winter storms in Japan havebeen investigated mainly from the perspective of heavy
snowfalls. The conditions that bring snowfall to Japanare mainly classified into “coastal” and “mountainous”
types (Fujita 1966; Iwamoto et al. 2008). The coastal
snowfall type occurs when a trough or a cold-core low
at the 500 hPa level develops over the Sea of Japan. A
convex isobar structure develops at the ground surface,
and westerly wind with a southern component is dominant. It snows mainly in the coastal areas of the Sea ofJapan, and it can become disaster-level heavy snowfall
when the Japan sea Polar air mass Convergence Zone
(JPCZ) develops (Asai 1988; Eito et al. 2010; Tachibana
et al. 2022). Winter thunderstorms develop typically inthe coastal type (Goto and Narita 1991). When a 500
hPa trough or cold-core low passes over to the Pacific
Ocean, the mountainous snowfall type develops. The
surface pressure pattern becomes a dense isobar witha north-south run, which strengthens the northern
winter monsoon. It provides heavy snowfalls mainly ininland mountainous areas due to the strong northernwinds and mountainous geographical effects.
Wada et al. (2021b) analyzed 11 gamma-ray glows
detected at Kanazawa University in Ishikawa, combined
them with X-band radar and disdrometer observations,and revealed that gamma-ray glows were always accompanied by convective clouds with a radar echo of >35 dBZ, and by precipitation of graupels. While microscale meteorological conditions of gamma-ray glows
have been studied, synoptic conditions have never been
discussed well. In particular, it remains unclear whattypes of synoptic conditions can create mesoscale conditions that facilitate glow detections at sea level. In
the present study, we discuss synoptic meteorologicalconditions during 70 gamma-ray glows in winter thunderstorms reported by Wada et al. (2021a), by utilizing weather charts, observations, numerical models,and meteorological satellite images. We mainly refer tosurface and 500 hPa meteorological charts to analyze
positions of lows, fronts, and pressure patterns. The
differences between glow-detection and non-detection cases are also investigated. Throughout the paper,time is described in UTC (universal coordinated time)
unless otherwise noted.

Wada et al. Progress in Earth and Planetary Science(2023) 10:6

2 Methods
We refer to 70 gamma-ray glows reported in Wada et al.
(2021a). The event list is shown in Table 1. The glow
events are divided into 24 groups based on detection
time, in order to focus on synoptic conditions rather than
microscopic ones. Cases 11, 18, 19, and 23 contain 5 ormore glows, and they are intensively analyzed in the following section.
We utilize surface analysis charts (ASAS) publishedevery 6 h by the Japan Meteorological Agency (JMA),
500 hPa constant-pressure charts (AUPQ35) publishedevery 12 h by JMA, infrared satellite images of the Himawari-8 Advanced Himawari Imager (AHI) Band 13/TIR1,
10 min surface observations by JMA Automated Meteorological Data Acquisition System (AMeDAS), and mesoscale numerical prediction models (MSM) of JMA. The
surface charts ASAS show isobaric lines of surface pressure in the unit of hPa, while the 500 hPa charts AUPQ35
show those of 500 hPa altitude in the unit of meter.
A typical altitude of 500 hPa is ∼ 5500 m. The infrared
satellite images of Himawari-8 provide brightness temperatures every 10 minutes with geolocation correction(Takenaka et al. 2020; Yamamoto et al. 2020), whose grid
resolution is 0.02◦ . MSM is published every 3 h, covers
N22.4◦–N47.6◦ and E120◦–E150◦ with a resolution of
0.1◦ (latitude) and 0.125◦ (longitude), and contains 39 h
or 51 h predictions for the surface (1 h interval) and highaltitudes (3 h intervals). In this study, initial analysis dataof temperature and geopotential height are utilized, andprediction data are not employed. We mainly refer tothese values at 850 hP altitude. The geopotential heightat 850 hPa is typically ∼ 1500 m, where convections
inside winter thunderclouds are active. The temperature
at 850 hPa is a common parameter for weather forecasts.
Average lapse rates between surface and 850 hPa height
are also calculated with surface temperature, temperature, and geopotential height at 850 hPa. Also, the altitude at − 10 ◦ C is calculated with MSM.
The observation sites of the GROWTH collaborations
are roughly separated into two areas: Kanazawa andKomatsu. The two areas are ∼ 25 km apart, as shownin Fig. 1. We refer to the Kanazawa AMeDAS station(N36.588◦ , E136.633◦ ) and the Komatsu AMeDAS station (N36.382◦ , E136.435◦ ) for surface observations oftemperature. The AMeDAS stations are shown in Fig. 1.
We also extract the temperature at 850 hPa and the lapse
rate between the surface and 850 hPa with the MSM
data, as mentioned above. Its base location is N36.6◦ ,E136.625◦ and N36.4◦ , E136.5◦ for the Kanazawa andKomatsu areas, respectively.
The wind direction and speed at the moment of glows
are retrieved from Wada et al. (2021a), estimated bypattern matching of X-band radar images. The region

Page 3 of 21

of the wind estimation is N36.4◦–36.7◦ , E136.4◦–136.8◦
for Kanazawa, and N36.25◦–36.55◦ , E136.2◦–136.6◦
for Komatsu. Considering the elevation angle of the
X-band radar, the estimated wind information is at ∼1 km altitude. The wind direction is where the◦ wind,
comes in clockwise. For example, 0 ◦ , 90◦ , 180 and270◦ indicate that winds blow from north to south,from east to west, from south to north, and from west
to east, respectively.
To investigate the lightning occurrence, we utilize theLIghtning DEtection Network system (LIDEN) of JMA(Ishii et al. 2014). Based on the LIDEN data, we produce
daily lightning maps around Ishikawa Prefecture and calculate flash rates. The flash rate corresponding to a glow
is calculated as follows: We count total lightning flashes(both cloud-to-ground and in-cloud flashes) from 5 minutes before to 5 minutes after the glow detection in a
20 km×20 km region centered at the detection site. Then,the number of flashes is divided by 10 minutes. If a lightning flash consists of multiple strokes, we consider the
position of the flash to be that of the first stroke.
Besides the glow-detection cases, this study also analyzes conditions that exhibit winter thunderstorms but
no gamma-ray glows. We focus on non-detection casesin Kanazawa because Kanazawa has more gamma-ray
monitors than Komatsu. The criterion of non-detection
cases is when gamma-ray monitors in Kanazawa werein operation but no gamma-ray glows were detected,
and when the Kanazawa local meteorological observatory of JMA reported lightning activities within 10 km of
the observatory. The extracted non-detection cases arealso confirmed with the daily lightning maps of LIDEN.
We exclude the 2016–2017 winter seasons because of
fewer gamma-ray monitors than in other seasons. The
wind direction and speed are estimated with the X-bandradar images as the same method as Wada et al. (2021a).
Note that the X-band radar was not in operation during the non-detection case 9, and instead C-band radar
images of JMA are utilized for the wind estimation. The
flash rates of the non-detection cases are extracted in thesame way as the glow cases, with a 10 min window anda 20 km×20 km region centered at the local observatory.
We employ the maximum rate during the non-detection
period.

3 Results
3.1 Glow‑detection cases

In this section, we first analyze Cases 11, 18, 19, and 23,
which include 5 or more gamma-ray glows, based on surface and 500 hPa analyses, and satellite images. The othercases are then analyzed. The list of gamma-ray glows ispresented in Table 1.

34

35

16

17

2018/01/13 03:01

2018/12/08 11:53

Kanazawa

Kanazawa

Komatsu

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Komatsu

Kanazawa

Kanazawa

Kanazawa

Komatsu

Komatsu

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Komatsu

Kanazawa

Komatsu

Komatsu

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Komatsu

Komatsu

Kanazawa

Area

5.1

1.1

3.2

1.2

1.2

− 0.4

2.2

2.2

1.6

2.2

2.0

2.0

1.6

1.8

2.7

5.8

5.8

4.0

4.9

4.9

4.9

6.6

4.0

5.0

6.8

6.8

6.8

6.8

− 0.4

6.1

5.7

9.7

5.9

5.9

7.2

Ground ( ◦C)

Temperature

− 6.8

− 8.6

− 6.4

− 7.8

− 7.8

− 10.1

− 6.1

− 6.1

− 7.1

− 6.5

− 6.5

− 6.5

− 6.9

− 6.6

− 9.5

− 5.8

− 5.8

− 7.1

− 7.1

− 7.1

− 7.1

− 5.9

− 4.0

− 3.9

− 3.8

− 3.8

− 3.8

− 3.8

− 11.8

− 5.8

− 6.0

0.2

− 3.2

− 2.4

− 3.2

850 hPa ( ◦C)

8.1

6.9

7.0

6.2

6.2

6.9

6.0

6.0

6.3

6.4

6.3

6.3

6.2

6.2

8.6

8.2

8.2

8.1

8.8

8.8

8.8

9.1

5.8

6.4

7.6

7.6

7.9

7.9

8.4

9.0

8.6

6.7

6.3

6.3

6.6

1.9

1.6

1.8

1.7

1.7

1.4

1.9

1.9

1.8

1.8

1.8

1.8

1.8

1.8

1.5

2.0

2.0

1.8

1.8

1.8

1.8

2.0

2.2

2.2

2.3

2.3

2.3

2.3

1.2

1.9

1.9

2.8

2.4

2.4

2.6

Lapse rate ( ◦ Altitude at −10 ◦ C (km)
C/km)

250

250

250

260

260

240

250

250

250

250

250

250

250

250

290

260

260

250

250

250

250

260

240

240

250

250

260

260

310

270

260

260

300

300

260

Direction ( ◦)

Wind

14.0

13.8

25.6

10.8

10.8

18.2

13.8

13.8

16.1

19.3

19.3

19.3

20.4

15.9

11.8

20.6

20.6

21.0

21.6

21.6

21.6

14.8

21.6

20.2

13.2

13.2

16.5

16.5

16.7

16.1

20.1

18.1

10.9

10.9

9.5

Speed (m/s)

0.0

0.2

0.0

0.0

0.0

0.2

0.7

0.4

0.0

0.2

0.5

0.5

0.0

0.0

0.1

0.0

0.0

0.0

0.0

0.0

0.0

0.2

0.0

0.9

0.2

0.2

0.2

0.3

0.0

0.3

0.7

0.3

0.0

0.0

0.0

Flash rate(flash/min)(2023) 10:6

2018/02/03 18:50

2018/01/23 04:29

32

33

15

2018/01/11 01:40

2018/01/13 03:01

30

31

13

2018/01/10 02:59

2018/01/10 03:02

28

29

2018/01/09 17:57

2018/01/09 22:34

26

27

14

12

2018/01/09 17:53

2018/01/09 17:54

24

25

2018/01/09 17:36

23

2018/01/02 18:19

2018/01/09 14:41

21

22

10

2017/12/25 23:10

2017/12/25 23:11

19

2017/12/11 08:52

2017/12/11 09:17

17

18

20

2017/12/11 08:49

2017/12/11 08:49

15

16

2017/12/05 03:07

2017/12/05 09:33

13

14

2017/12/04 18:27

2017/12/05 02:51

12

11

9

8

7

11

2017/02/05 20:10

2017/12/04 18:27

10

9

6

2017/01/14 20:30

2017/02/05 20:06

7

8

4

5

2017/01/12 16:43

2017/01/12 20:05

5

6

3

2016/12/07 17:58

2016/12/09 07:29

3

4

2

2016/12/07 15:13

2016/12/07 17:56

1

1

Detection time (UTC)2

Event no.

Case no.

Table 1 List of gamma-ray glows recorded in Kanazawa and Komatsu areas

Wada et al. Progress in Earth and Planetary Science
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2018/12/17 14:17

2019/01/25 11:44

2020/01/12 17:06

2020/02/17 16:35

2020/03/15 21:28

69

70

2020/02/17 16:29

2020/02/17 16:30

67

2020/02/17 12:53

66

68

2020/02/17 12:51

2020/02/17 12:52

64

65

2020/02/17 12:49

2020/02/17 12:49

62

63

2020/02/17 12:00

2020/02/17 12:47

60

61

2020/02/17 11:52

58

59

2020/01/12 17:03

2020/01/12 17:05

56

57

2020/01/12 17:03

55

54

2019/01/21 16:03

2019/01/25 11:43

53

52

2018/12/18 14:51

2019/01/21 15:51

50

51

2018/12/18 14:42

2018/12/18 14:49

48

49

2018/12/18 14:42

2018/12/18 14:42

46

47

2018/12/18 14:40

44

45

2018/12/17 10:15

2018/12/17 14:15

42

43

2018/12/17 09:54

2018/12/17 10:15

40

41

2018/12/17 09:51

2018/12/17 09:54

38

2018/12/08 12:09

2018/12/08 12:10

36

37

39

Detection time (UTC)Event no.

Kanazawa

Komatsu

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Kanazawa

Area

5.5

4.1

1.9

1.1

1.1

2.6

2.6

2.6

2.6

2.6

2.6

2.4

2.5

6.2

6.2

6.2

6.2

2.8

2.8

4.2

5.6

6.6

6.6

8.1

8.1

8.1

8.1

8.4

8.4

5.9

5.9

7.7

7.7

7.7

5.5

◦

Ground ( C)

Temperature

− 7.5

− 6.1

− 7.7

− 7.0

− 6.9

− 6.9

− 6.9

− 6.9

− 6.9

− 6.9

− 6.9

− 6.9

− 2.6

− 2.6

− 2.6

− 2.6

− 4.5

− 4.5

− 5.7

− 5.7

− 4.7

− 4.7

− 4.7

− 4.7

− 4.7

− 4.7

− 4.2

− 4.2

− 2.2

− 2.2

− 2.2

− 2.2

− 2.2

− 6.8

− 6.8

850 hPa ( C)
◦

7.6

6.9

6.5

6.0

7.0

7.0

7.0

7.0

7.0

7.0

6.9

6.9

6.3

6.3

6.3

6.3

5.2

5.2

7.0

8.0

7.7

7.7

8.8

8.8

8.8

8.8

9.0

9.0

5.8

5.8

7.1

7.1

7.1

8.4

8.4

1.8

1.7

1.7

1.8

1.8

1.8

1.8

1.8

1.8

1.8

1.8

1.8

2.5

2.5

2.5

2.5

2.1

2.1

2.0

2.0

2.2

2.2

2.2

2.2

2.2

2.2

2.2

2.2

2.6

2.6

2.6

2.6

2.6

1.9

1.9

Lapse rate ( ◦ Altitude at −10 ◦ C (km)
C/km)
◦

280

260

260

260

250

250

250

250

250

250

260

260

240

240

240

240

260

260

270

280

270

270

270

270

270

270

280

280

270

270

270

270

270

250

250

Direction ( )

Wind

13.0

13.6

12.7

12.7

15.0

15.0

15.0

15.0

15.0

15.0

15.7

15.7

16.4

16.4

16.4

16.4

16.9

16.9

13.6

14.2

11.9

11.9

13.5

13.5

13.5

13.5

11.3

11.3

10.6

10.6

10.9

10.9

10.9

14.0

14.0

Speed (m/s)

0.3

0.1

0.2

0.2

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.1

0.4

0.5

0.7

0.7

0.1

0.1

0.4

1.1

1.0

1.3

1.1

1.1

1.3

1.3

0.0

0.0

0.0

0.0

1.1

1.1

0.9

0.0

0.0

Flash rate(flash/min)(2023) 10:6

24

23

22

21

20

19

18

Case no.

Table 1 (continued)

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Fig. 1 Maps around Japan and Ishikawa Prefecture. a A map of Japan with region names. The red rectangle shows the area shown in theright panel. b A map of Ishikawa Prefecture. Red stars show the Kanazawa and Komatsu AMeDAS stations. The Kanazawa local meteorologicalobservatory is located at the same place as the Kanazawa AMeDAS station. The blue mesh indicates the MSM grid. Black lines on the maps are
prefectural boundaries

3.1.1 Case 11 (9 January 2018)

In Case 11, 5 gamma-ray glows were detected between
14:00 and 18:00, on 9 January 2018, in Kanazawa andKomatsu. The meteorological charts are shown in Fig. 2.
As seen in the surface analysis, there is a developed low
with an occluded front at the northeast of Hokkaido, anda low without fronts at Hokkaido. A convex of surface
isobaric lines is formed from Kanto toward the low without fronts, and the direction of the surface isobaric lineschanges around Hokuriku.
At 500 hPa height, there is a cold-core low at Hokkaido
which is associated with the low without fronts. Also,
constant-pressure isobaric lines run east and west above
the main island of Japan, and a cold-air mass of − 30 ◦Cor colder flows into the Hokuriku region at 500 hPa.
When the low-pressure center is northeast of Kanazawa,then the westerly wind around the low (counterclockwise) is present over the warm Sea of Japan, which sets
up strong instability and moist convection and brings
thunderstorms to the island of Japan.
As seen in the infrared image of the Himawari-8 satellite, there are streak clouds on the Sea of Japan, flowing from the Korean Peninsula to the east to the coastal
areas of Japan. In particular, tall convective clouds with abrightness temperature of < −250 K develop on the landof Hokuriku. At the moment of glow detection, the windblew from west-southwest. The temperature at the surface (measured by AMeDAS) and 850 hPa (provided byMSM) was around 2 ◦ C and − 7 ◦ C, respectively. The −10 ◦ C altitude calculated with MSM was 1.8 km.

Flash rates are presented in Table 1. No lightning
flashes were detected around the detection time of
two glows in Komatsu (Events 22 and 23), while 0.2–
0.5 flashes per minute in Kanazawa (Events 24–26). The
median of the flash rates is 0.2 flashes per minute.
3.1.2 Case 18 (17 December 2018)

In Case 18, 7 gamma-ray glows were detected between
09:00 and 15:00, on 17 December 2018, in Kanazawa.
The meteorological charts are shown in Fig. 3. At the surface there is a low with a cold front in the east of Tohoku,
going northeast. Also, there is another low without fronts
in the northeast of Hokkaido, going northward. Thereis a convex structure of surface isobaric lines aroundthe Hokuriku region. At 500 hPa, a trough is passing
above Hokuriku at the moment of the glow detections,while no cold-core low is detected. Associated with thetrough, a cold-air mass of − 24 ◦C or colder flows into the
Hokuriku region.
In the satellite image, there are clouds with a brightness
temperature of 250–260 K on the Sea of Japan, and convective clouds with a brightness temperature of < 250 K.
At the moment of glow detection, the wind blew fromthe west. The temperature at the surface and 850 hPa wasaround 7 ◦ C and − 3 ◦ C, respectively. The − 10 ◦ C altitude was 2.2–2.6 km.
During Events 38–40, there was a relatively active
thunderstorm around the detection site, with flash rates
of 0.9–1.1 flashes per minute. On the other hand, nolightning flashes were detected during Events 41–44.

Wada et al. Progress in Earth and Planetary Science(2023) 10:6

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Fig. 2 Meteorological charts of the glow-detection Case 11. a An expanded view of JMA surface analysis (ASAS). b An expanded view of JMA 500
hPa analysis (AUPQ35). c Brightness-temperature heat map taken by Himawari-8 Advanced Himawari Imager IR1 (band 13). d Daily lightning map
based on the LIDEN observation

3.1.3 Case 19 (18 December 2018)

In Case 19, 6 gamma-ray glows were detected between
14:00 and 15:00, on 18 December 2018, in Kanazawa.
This case occurred one day after Case 18. The charts
are in Fig. 4. The low without fronts related to Case 18
moved to the north of Sakhalin, and the low with fronts
reached the Kamchatka peninsula. The convex structurearound Hokuriku is more developed than Case 18.
At 500 hPa, the trough passing above the main island ofJapan in Case 18 moved to the east of Japan, and anothertrough is passing above Hokuriku around 15:00. Also,a cold air mass goes southward, and the temperature at
Hokuriku is less than − 30 ◦C.
Like Case 18, there is a cluster of clouds with a brightness temperature of 250–260 K on the Sea of Japan, andalso convective clouds with a brightness temperature of< 250 K on the land of Hokuriku, as seen in the satellite
image. The west wind blows, and the surface and 850
hPa temperature is around 7 ◦ C and − 5 ◦ C, respectively.
Compared to Case 18, the surface temperature is almost
the same, but the 850 hPa temperature is lower. The − 10◦
C altitude was 2.2 km.

Wada et al. Progress in Earth and Planetary Science(2023) 10:6

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Fig. 3 Meteorological charts of the glow-detection Case 18 in the same format as Fig. 2

The LIDEN lightning map shows that lightning discharges occurred in Ishikawa Prefecture all day. The
flash rates are above 1.0 flash per minute, with a medianof 1.2 flash per minute. Among the 24 detection cases,
this case had the most active thunderstorm during glow
detections, based on the flash rates.
3.1.4 Case 23 (17 February 2020)

In Case 23, 11 gamma-ray glows were detected between
11:00 and 17:00, on 17 February 2020. This is the largest number of gamma-ray glows per day in the glow
catalog of Wada et al. (2021a). The charts are in Fig. 5.
There is a developed low with an occluded front in theeast of Hokkaido, and another low without fronts in thewest of Hokkaido. At 500 hPa, a cold-core low associatedwith the low without fronts exists. Since a spiral clusterof convective clouds with a brightness temperature of< 250 K centered at the low is seen in the satellite image,this low is considered to be a polar low.
There is another low without fronts at the surface
in the east of Kanto. Also, a convex structure of surface isobaric lines is seen around Hokuriku, as in thethree cases above. Isobaric lines at 500 hPa form an
ellipse, centered at the polar low. A trough at 500 hPa
is passing above Kyushu, yet not above Hokuriku at
the moment of glow detection. Tall clouds with aWada et al. Progress in Earth and Planetary Science(2023) 10:6

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Fig. 4 Meteorological charts of the glow-detection Case 19 in the same format as Fig. 2

brightness temperature of < 240 K form along the isobaric lines at 500 hPa, as seen in the satellite image.
In particular, the land of Ishikawa Prefecture is completely covered by convective clouds. At the momentof glow detection, the wind blows from the west or
west-southwest. Surface and 850 hPa temperature isaround 2 ◦ C and − 7 ◦ C, respectively. The − 10 ◦ C
altitude was 1.7–1.8 km.
The lightning activity was quite low. Among 11
glows, no lightning flashes were detected during 7
glows. And the flash rates during the detection of theother glows are 0.2 flashes per minute at most.

3.1.5 Summary of glow‑detection cases

We analyze all 24 cases including the four cases
described above. The charts of all the cases are
uploaded to a data repository (see the Availability ofdata and material section). Figure 6 shows histogramsof surface and 850 hPa temperature, lapse rate, andwind direction for the glow-detection cases. We utilize
the median of each value when a glow-detection caseincludes multiple gamma-ray glows. The average valueof surface and 850 hPa temperature, lapse rate, − 10 ◦ C
altitude, and wind direction is 4.3 ◦C, − 5.8 ◦C, 7.3 ◦C/km, 2.0 km, and 260◦ , respectively.

Wada et al. Progress in Earth and Planetary Science(2023) 10:6

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Fig. 5 Meteorological charts of the glow-detection Case 23 in the same format as Fig. 2

The glow-detection cases can be classified into five
types. (1) Having a convex structure at the surface
around the Hokuriku region (convex type; Cases 1, 3, 6,
8, 9, 11, 12, 16, 17, 18, 19, 20, 22, and 24). (2) Hit by thesouth edge of a polar low (PL type; Cases 5,10,13,15, and23). (3) Directly hit by a small low without fronts (smalllow type; Cases 7, 14, and 21). (4) A passage of a cold
front (cold-front type; Case 2). And (5) Heavy-snow condition (snowy type; Case 4). Most of the cases are classified into the first three types, and the latter two cases
are exceptions. This classification, the existence of coldcore lows, the passage of a trough, and a cold front aresummarized in Table 2. Cold-core lows exist in 20 of the

24 cases. Besides, the existence of JPCZ that reaches themain island of Japan is investigated based on satellite
infrared images, and also, it is tested if Kanazawa is hit by
L-mode (longitudinal mode; the cloud strike is parallel tothe wind direction), T-mode (transversal mode; the cloud
strike is perpendicular to the wind direction), or Cu-Cb(convergence zone between L and T-modes) clouds when
JPCZ is confirmed, as in Table 2.
Fourteen cases, the largest number, are classified into
the convex type. A typical example is Case 19. There is ahigh in the southwest of Kyushu and a low in the northof Hokkaido. In the region between the high and low,
surface isobaric lines run from northwest to southeast,Wada et al. Progress in Earth and Planetary Science(2023) 10:6

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Fig. 6 Histograms of meteorological parameters in the glow-detection cases. a Surface temperature measured by AMeDAS stations. b The
temperature at 850 hPa extracted from MSM. c Lapse rate between surface and 850 hPa height calculated with MSM. d Wind direction derived withradar images. The wind direction is where the wind comes from clockwise. For example, the direction 270◦ indicates that wind comes from the west
toward the east

but the isobaric lines have a bend and form a convex
structure around Hokuriku. This convex structure corresponds to a trough at 500 hPa. The strikes of the isobars
at the surface are in the east-west direction on the northwest side of the convex, and hence, westerly wind tends
to predominate from the surface to high altitudes around
Hokuriku. In many cases, cold-core lows exist, and many
correspond to the passage of troughs. There are cases
in which a steep trough is passing above as in Case 24,
although cold-core lows are not seen. In addition, there
are cases where the convex structure is formed due to theeffects of multiple lows, even when a trough is not passing, as in Case 16.
Five cases are classified into the PL type. A typical example is Case 5. The charts of Case 5 are shownin Fig. 7. In the satellite image, a cluster of developed
clouds is seen in the north of the polar low. Besides,
another cluster of streaked and developed clouds islocated 500 km south of the polar-low center and covers the Hokuriku region. In fact, lightning strikes areobserved along the coast of the Sea of Japan, including

the Hokuriku region covered by the streaked clouds, asseen in the LIDEN daily lightning map. Also in othercases, convective clouds that develop along the 500 hPa
contour line can be confirmed several hundred kilometers away from the low, apart from developed clouds thatdeveloped around the polar low. Isobaric lines at the surface are similar to the convex type.
Three cases are classified into the small-low type. A
typical example is Case 7. The charts of Case 7 are shownin Fig. 8. A small low without fronts developed over the
Sea of Japan is approaching the Hokuriku region. At thistime, in the satellite image, there are developed convective clouds surrounding the low, and it covers the vicinityof Kanazawa. Also in other cases, low-pressure disturbances centered on the Hokuriku region are confirmedby satellite images. At 500 hPa, the cold-core low is confirmed in the north of the small lows in Cases 7 and 21.
The passage of troughs at 500 hPa is not clear for thethree cases.
Only Case 2 is categorized as the cold-front type.
This is one of the two exceptions. The charts are shown

Yes

Yes

No

No

No

PL

Cold-front

ND10

ND11

Yes

Yes

Yes

No

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

No

Yes

Yes

Yes

Unclear

No

Yes

No

Yes

No

No

Yes

Yes

No

No

No

No

No

No

No

No

No

No

No

No

No

No

Yes (Cu-Cb)

No

No

No

No

No

Yes (L-mode)No

No

Yes (Cu-Cb)

Yes (Cu-Cb)

No

5.8

4.1

2.6

6.2

2.8

4.9

8.1

7.7

5.5

1.1

3.2

1.2

− 0.4

2.2

2.0

2.7

7.6

7.9

16.1

5.2

5.9

3.7

8.8

5.5

9.2

11.0

3.4

− 2.2

6.0

− 4.1

− 3.8

− 7.7

− 0.8

− 3.5

− 3.2

− 1.8

− 0.6
− 4.8

0.4

− 5.8

− 6.1

− 6.9

− 2.6

− 4.5

− 5.7

− 4.7

− 2.2

− 6.8

− 8.6

− 6.4

− 7.8

− 10.1

− 6.1

− 6.5

− 9.5

− 5.8

− 7.1

− 4.0

− 3.8

− 3.8

− 5.9

− 11.80.2− 3.2

850 hPa ( C)
◦

7.1

7.1

6.9

6.8

8.1

6.9

6.4

8.7

8.8

5.6

5.8

7.0

7.3

7.6

7.0

6.3

5.2

7.5

8.8

7.1

8.4

6.9

7.0

6.2

6.9

6.0

6.3

8.6

8.2

8.8

6.4

7.6

7.9

8.4

8.8

6.7

6.3

Lapse rate
( ◦C/km)

2.6

3.8

2.1

2.4

1.7

2.8

2.3

2.4

2.6

2.2

2.9

3.0

2.0

1.8

1.8

2.5

2.1

2.0

2.2

2.6

1.9

1.6

1.8

1.7

1.4

1.9

1.8

1.5

2.0

1.8

2.2

2.3

2.3

1.2

1.9

2.8

2.4

Altitude at −10 ◦ C (km)

260

260

250

260

270

250

250

250

270

250

250

260

260

280

250

240

260

275

270

270

250

250

250

260

240

250

250

290

260

250

240

250

260

310

265

260

300

0.33

0.2

0.7

1.0

0.2

0.3

0.2

0.3

0.2

0.3

0.1

0.1

0.23

0.3

0.0

0.6

0.1

0.75

1.2

0.0

0.0

0.2

0.0

0.0

0.2

0.4

0.2

0.1

0.0

0.0

0.2

0.2

0.25

0.0

0.5

0.3

0.0

Wind
Flash rate
direction ( ◦) (flash/min)(2023) 10:6

(Average)

PL

Cold-front

ND8

ND9

Cold-front

Convex

ND6

ND7

Quasi-convex

Cold-front

ND4

ND5

ConvexConvex

ND2

ND3

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No
No

4.9

5.0

6.8

6.8

5.9
− 0.4

4.3
No

Yes

No

Yes

No

No

Yes

Yes

No

No

Yes

Unclear

No

No

No
No

Yes (Cu-Cb)
Yes (L-mode)

5.9
9.7

◦

Ground ( C)

Temperature

10.5

Yes

UnclearUnclearNoNo

No

Yes (Cu-Cb)

No

Yes (L-mode)

No

No

JPCZ (at Kanazawa)

Convex

No

No
Yes

No

No

No

No

Yes

No

Passage ofcold front

ND1

PL

Convex

23

24

Yes

Yes

Yes

No

No

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

UnclearYes

Yes

Passage of trough(Average)

Small-low

Convex21

22

ConvexConvex19

20

ConvexConvex

17

18

PL

Convex

15

16

PL

Small-low13

14

ConvexConvex11

12

Convex

PL

9

10

Yes

Small-low

Convex

7

8

Yes

Yes

PL

Convex

5

Yes

Yes

Yes

No

Cold-core low

6

Convex

Snowy

3

4

ConvexCold-front

1

2

Type

Case no.

Table 2 List of parameters for glow-detection and non-detection cases

Wada et al. Progress in Earth and Planetary Science
Page 12 of 21

Wada et al. Progress in Earth and Planetary Science(2023) 10:6

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Fig. 7 Meteorological charts of the glow-detection case 5 in the same format as Fig. 2

in Fig. 9. A large number of lightning discharges wereobserved along the coast of the Sea of Japan as seen in
the LIDEN lightning map, but the flash rate around thedetection time is relatively low, 0.3 flashes per minute,and only one gamma-ray glow was detected. The cold
front at 06:00 has a kink at Ishikawa, indicating that asmall low is developing at Ishikawa. At that moment a
trough at 500 hPa was passing above.
The other exception is Case 4, classified into thesnowy type. The charts are shown in Fig. 10. Surface
isobaric lines run from north to south, and there is acold-core low at 500 hPa in the east of Tohoku. Thiscondition is similar to the mountainous snowfall type,

rather than the coastal type. Streaked clouds fromthe northwest flow into the coast of the Sea of Japan,
as seen in the satellite image. At this moment, JMA
reported heavy snow in this area. A cold air mass of< − 36 ◦C flows into the Hokuriku region. Surface and
850 hPa temperature is significantly lower than in othercases, − 0.4 ◦C and − 11.8 ◦C, respectively. The winddirection at the surface is 310◦ , which brings cold air
into Hokuriku from the northwest. LIDEN reported not
many but a few lightning strikes over a wide area along
the coast of the Sea of Japan. In fact, no lightning flash
was detected around the glow detection by LIDEN.

Wada et al. Progress in Earth and Planetary Science(2023) 10:6

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Fig. 8 Meteorological charts of the glow-detection case 7 in the same format as Fig. 2

3.2 Non‑detection cases

In order to compare the meteorological conditions
between glow-detection and non-detection cases, we
extract non-detection cases where gamma-ray glows
were not detected even though lightning discharges
were occurring around Kanazawa. During the period
when gamma-ray monitors of the GROWTH collaboration were in operation, candidate cases in which lightning activities within 10 km from Kanazawa are reportedby the Kanazawa local meteorological observatory are
selected. The 10 km distance from the Kanazawa local
meteorological observatory is set to cover our observation network in Kanazawa. Then, 11 candidates are

selected as non-detection cases, in which lightning discharges around Kanazawa are confirmed also by the
LIDEN daily lightning maps. The list of the non-detection
cases is summarized in Table 3. The maximum flash ratesof the non-detection cases vary from 0.1 to 1.0 flashes
per minute. The charts of all the non-detection cases
are uploaded to a data repository (see the Availability ofdata and material section). Figure 11 shows histogramsof surface and 850 hPa temperature, lapse rate, and winddirection for the non-detection cases. The average valueof surface and 850 hPa temperature, lapse rate, − 10 ◦ C
altitude, and wind direction is 7.9 ◦C, − 2.2 ◦C, 7.1 ◦C/km,
2.6 km, and 260◦ , respectively.

Wada et al. Progress in Earth and Planetary Science(2023) 10:6

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Fig. 9 Meteorological charts of the glow-detection Case 2 in the same format as Fig. 2

The non-detection cases are also classified into fourtypes. Four cases are classified into the convex type
(Cases ND1, ND2, ND3, and ND7), four cases into thecold-front type (Cases ND5, ND6, ND9, and ND11),
two cases into the PL type (Cases ND8 and ND10), andCase ND4 into a derivative of the convex type (quasiconvex type). Cold-core lows at 500 hPa are confirmed
for 10 non-detection cases, except for Case ND9. JPCZ is
not confirmed for each case.
In Case ND4, there are two developed lows in the northof Hokkaido, and a corresponding cold-core low is confirmed at 500 hPa. The charts are shown in Fig. 12. On
the other hand, an anticyclone is located in the south of

Kyushu. The isobars at the surface in the Hokuriku region
between the low in the north and the anticyclone in thesouth run from east to west and are parallel to those at
500 hPa. Although the convex structure was not found in
the surface analysis, it is classified as a derivative of theconvex type because the wind over the Sea of Japan isconsidered to be similar to that of the convex type.

4 Discussion
The glow-detection cases are found to be classified into
mainly three types (convex, PL, and small-low types),with two exceptions. In particular, the convex type is themost typical condition of gamma-ray glows as 14 of 24

Wada et al. Progress in Earth and Planetary Science(2023) 10:6

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Fig. 10 Meteorological charts of the glow-detection case 4 in the same format as Fig. 2

cases are classified into it. Also, cold-core lows are foundin the north of Japan in most of the glow-detection cases.
Therefore, convective clouds are considered to be produced by an unstable atmosphere with cold air mass athigh altitudes provided by the cold-core lows. A highconvective available potential energy (CAPE) value canbe observed during winter thunderstorms (Takahashi
et al. 2019).
One of the common features between the glow-detection and non-detection cases is that most of both cases
occurred when west or west-southwest winds blew at
the surface. Fujisawa and Kawamura (2005) reported
that west winds with a south component were dominantduring winter thunderstorms in the western region of
Noto Peninsula (including Ishikawa Prefecture). This
report is consistent with the present study. In the PL,
small-low, and cold-front types, mesoscale disturbances
are considered to provide westerly winds. On the other
hand, there are no surface lows nor mesoscale disturbances on the Sea of Japan in some convex-type casessuch as Case 19. In these cases, west and southwest winds
are thought to dominantly blow along isobars at the surface. West and southwest winds are parallel to the Tsushima warm current, which blows along the coast of the
Sea of Japan, and hence, the atmosphere at the surface
gets warm and wet before reaching the Hokuriku region.

Wada et al. Progress in Earth and Planetary Science(2023) 10:6

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Table 3 List of non-detection cases in Kanazawa area
Case no. Period (UTC)

Representative
time (UTC)

Temperature

Lapse
rate ( ◦C/
Ground ( ◦C) 850 hPa ( ◦C) km)

Altitudeat − 10 ◦ C
(km)

Wind
Direction ( ◦) Speed (m/s)

Maximum flash
rate (flash/min)1

2017/12/04
05:30-06:20

2017/12/04 06:00 10.5

0.4

7.0

3.0

260

10.4

0.1

2

2017/12/04
12:40-14:00

2017/12/04 13:20 7.6

− 0.6

5.8

2.9

250

11.9

0.1

3

2017/12/18
21:40-00:30

2017/12/18 23:10 3.4

− 4.8

5.6

2.2

250

17.9

0.3

4

2018/12/19
08:20-09:20

2018/12/19 08:50 11.0

− 1.8

8.8

2.6

270

18.8

0.2

5

2019/01/23
11:10-11:20

2019/01/23 11:20 9.2

− 3.2

8.7

2.4

250

16.1

0.3

6

2019/01/28
06:50-07:00

2019/01/28 07:00 5.5

− 3.5

6.4

2.3

250

22.0

0.2

7

2019/03/12
07:40-08:20

2019/03/12 08:00 8.8

− 0.8

6.9

2.8

250

15.6

0.3

8

2019/03/13
10:50-11:10

2019/03/13 11:00 3.7

− 7.7

8.1

1.7

270

17.1

0.2

9

2020/01/19
10:00-11:40

2020/01/19 10:50 5.9

− 3.8

6.8

2.4

260

19.3

1.0

10

2020/03/15
08:40-09:10

2020/03/15 09:00 5.2

− 4.1

6.9

2.1

250

16.3

0.7

11

2020/03/22
00:20-00:50

2020/03/22 00:40 16.1

6.0

7.1

3.8

260

24.9

0.2

Vigorous convections are facilitated between a warm surface atmosphere above the Tsushima current and a cold
atmosphere at high altitude (Goto and Narita 1991).
There is no significant difference in flash rates between
the glow-detection and non-detection cases. The maximum flash rate in the glow-detection cases is 1.3 flashes
per minute around Events 45, 46, and 49 in Case 19. On
the other hand, no lightning flashes were detected around
31 glow events among 70. The rates in the non-detection
cases are from 0.1 to 1.0 flashes per minute. The average flash rate of the non-detection cases, 0.33 flashes per
minute, is larger than that of the glow-detection case, but
the maximum one, 1.0 flash per minute, is lower thanthat of the glow-detection case, 1.3 flashes per minute.
One of the differences between the glow-detection andnon-detection case is the temperature at the surface and
850 hPa. While the average temperature at the surface
and 850 hPa for the glow-detection cases is 4.3 ◦ C and− 5.8 ◦ C, respectively, that for the non-detection cases is
7.9 ◦ C and − 2.2 ◦ C, respectively. Both temperatures atthe surface and 850 hPa in the non-detection cases are
3–4 ◦ C higher than the glow-detection cases. When analyzing individual cases, the surface temperature exceeds
10 ◦ C in Cases ND1, ND4, and ND11, and even the 850
hPa temperature exceeds 0 ◦ C in Cases ND1 and ND11.
The charge structure of thunderclouds is temperature-dependent. Zheng et al. (2019) utilized a lightning

mapping array in the very-high-frequency band toinvestigate winter thunderstorms in Japan and revealed
that the main charging process occurred at around or
below − 10 ◦C level. Takahashi et al. (2019) performed
sonde observations of charged precipitation particles
and documented the temperature-dependent charge
structure. In the context of gamma-ray observations,
Williams et al. (2022) combined radar and surface
electric-field observations with TGE observations inArmenia. They found a clear difference in the verticalstructure of radar echoes between TGEs with negativeand positive surface electric-field excursions, when thevertical structure is investigated in vertical temperature
profiles.
In the non-detection cases with a high-temperaturefield, the altitude where electrification intensively occurs
should get higher than in the other cases. The averagetemperature at the surface is 4.3 ◦ C and 7.9 ◦ C for the
glow-detection and non-detection cases, respectively,
with a difference of 3.6 ◦ C. In the same way, the averagetemperature at the 850 hPa level is − 5.8 ◦ C and − 2.2◦
C, respectively, with a difference of 3.6 ◦ C. Assuming alapse rate of 7 ◦C/km, the temperature difference of 3.6◦
C corresponds to ∼ 0.5 km. This difference can be also
confirmed by the − 10 ◦ C altitude as the average altitudeat − 10 ◦ C of non-detection cases is 0.6 km higher thanthat of glow-detection cases.

Wada et al. Progress in Earth and Planetary Science(2023) 10:6

Page 18 of 21

Fig. 11 Histograms of meteorological parameters in the non-detection cases, presented in the same format as Fig. 6This difference in the distance to the electrified regionis critical for photon attenuation in the atmosphere, as
the mean free path is 0.22 km for 3 MeV photons, a representative photon energy of gamma-ray glows. Therefore, it will become more difficult to detect gamma-ray
glows at sea level in higher temperature fields of the nondetection cases as the altitude where electrons are accelerated and gamma rays are produced gets higher. Except
for Case 2, the temperature at 850 hPa is lower than
− 2 ◦C in the glow-detection cases. Therefore, it is considered difficult to observe gamma-ray glows at sea levelin Cases ND1, ND2, ND4, ND7, and ND10 even if electron acceleration occurs inside thunderclouds.
The second difference is a direct hit by a small low. In
three of the 24 glow-detection cases, a small low without
fronts was passing above Ishikawa at the moment of glow
detections. On the other hand, there are no non-detection cases of the small-low type. Although the small-low
type does not frequently occur, gamma-ray glows tend to
be detected once a small-low case occurs.
The third difference is the cold-front type. While only
one case among the 24 glow-detection cases is the coldfront type, 4 in 11 non-detection cases are classified into

this type. Cold fronts consist of a lower cold layer and awarm layer above, and convection occurs as the warm
layer is lifted by running on the cold layer. Therefore, theambient temperature is relatively high during the passage of cold fronts. The temperatures at 850 hPa of Case
2, ND5, ND6, ND9, and ND11 are higher than the average one of the glow-detection cases. Similar to the firstdifference, the electrification altitude should be highduring the passage of a cold front, making gamma-ray
glows difficult to observe on the ground. In Case 2, thecold front had a kink at Ishikawa. It indicates that a small
low is developing above Ishikawa. Thus, Case 2 might bea hybrid of the cold-front type and the small-low type.
There is no kink nor small lows in the non-detection
cases of the cold-front type.
While some non-detection cases have clear differencesfrom the glow-detection cases, there are non-detection
cases that have a similar condition to the glow-detection
cases. As mentioned above, the mean free path of 3 MeV
photons is 0.22 km. This is applicable not only for vertical penetration of photons but also for a horizontal one.
It means that gamma-ray glows are detectable roughly
within 1 km from their radiation center since gamma raysWada et al. Progress in Earth and Planetary Science(2023) 10:6

Page 19 of 21

Fig. 12 Meteorological charts of the non-detection case ND4 in the same format as Fig. 2

are attenuated in the atmosphere. Therefore, gamma-ray
glows can be only detected when a thundercloud emitting gamma rays is passing directly above detectors. In
Cases ND3, ND8, and ND10, whose meteorological conditions are similar to the glow-detection cases, it is possible that gamma-ray glows occurred and were detectable
at sea level, but were missed by gamma-ray monitors as
the glows did not pass directly above them.

5 Conclusions
In the present study, we investigated synoptic conditions suitable for gamma-ray glow detections at sea level.
Twenty-four cases containing 70 gamma-ray glows,

detected in the Kanazawa and Komatsu areas by the
GROWTH collaboration between December 2016 andMarch 2020, were classified into three types and two
exceptions, based on surface and 500 hPa analyses, MSM,
AMeDAS, radar, and satellite observations. Most of theglow-detection cases were categorized as the convex typewith curved isobars at the surface, the PL type with a distant polar low, and the small-low type, where a small low
directly hits the Hokuriku region. The convex type is themost typical in the glow-detection cases as 14 in 24 are categorized, and most of the convex types are associated witha passage of a trough at 500 hPa. In almost all the cases, thewesterly or west-southwest wind was predominant.

Wada et al. Progress in Earth and Planetary Science(2023) 10:6

In addition, we analyzed 11 non-detection cases
between December 2017 and March 2020, in which
gamma-ray glows were not detected even though lightning discharges were occurring around Kanazawa.
They were classified into the convex type, the PL type,
and the cold-front type. Major differences from theglow-detection cases are that more cold-front cases,
no small-low cases, higher average temperature bothat surface and 850 hPa, and higher altitude at − 10 ◦ C.
The difference in average temperature, 3.6 ◦ C, corresponds to ∼ 0.5 km, which is critical for atmosphericattenuation of gamma rays. Therefore, it would be difficult to detect gamma-ray glows in the cold-front andhigher-temperature conditions due to more gamma-ray
attenuation in the atmosphere than in the glow-detection cases, while gamma-ray glows are likely detected
in a small-low condition. On the other hand, there aresome non-detection cases where no significant difference from the glow-detection cases is found. In thosecases, gamma-ray glows could have occurred, but thunderclouds emitting gamma rays could have passed far
from detectors, and thus, our detection network did
not catch them.
Abbreviations
AHI	Advanced Himawari Imager
AMeDAS	Automated Meteorological Data Acquisition System
ASAS	Analysis Surface Asia
AUPQ35	Analysis Upper Western North Pacific 300/500 hPa
GROWTH	Gamma-ray Observation of Winter Thunderclouds
JMA	Japan Meteorological Agency
JPCZ	Japan sea Polar air mass Convergence Zone
JST	Japan Standard Time
LIDEN	LIghtning DEtection Network
MSM	Meso-scale numerical prediction model
ND	Non-detection
PL	Polar low
UTC​	Coordinated universal time
Acknowledgements
This work is based on the gamma-ray glow observations performed by theGamma-Ray Observation of Winter Thunderclouds (GROWTH) collaboration. The datasets and charts produced by Japan Meteorological Agency
are provided via Data Integration and Analysis System (DIAS), Certified andAccredited Meteorologists of Japan (CAMJ), Research Institute of Sustainable
Humanosphere, Kyoto University, and Center for Environmental Remote Sensing (CEReS), Chiba University
Author contributions
YW leads analysis, discussion, and manuscript drafting. MT contributes toanalysis and discussion. SH contributes to LIDEN data curation and discussion. KM contributes to discussion and interpretation. All authors read andapproved the final manuscript.
Funding
This work is supported by JSPS KAKENHI Grant Numbers 21H01116 and
22K14453.
Availability of data and materials
The datasets used in this article are available online (https://doi.
org/10.17632/2t6n5x986h.2). The MSM and synthetic radar datasets areprovided by Japan Meteorological Agency via the Research Institute ofPage 20 of 21

Sustainable Humanosphere, Kyoto University (http://database.rish.kyoto-u.
ac.jp/arch/jmadata/). XRAIN data are provided by the Ministry of Land,
Infrastructure, Transport and Tourism via Data Integration and Analysis System(DIAS). Surface and constant-pressure charts are provided by Japan Meteorological Agency via Certified and Accredited Meteorologists of Japan (CAMJ).
Data from the Himawari-8 satellite are provided by Japan Meteorological
Agency via Center for Environmental Remote Sensing (CEReS), Chiba University (http://www.cr.chiba-u.jp/japanese/database-himawari.html).

Declarations
Competing interests
The authors declare that they have no competing interests.
Received: 2 June 2022 Accepted: 4 February 2023

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