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Analysis of a Gigantic Jet in Southern China: Morphology,
Meteorology, Storm Evolution, Lightning, and Narrow
Bipolar Events
Jing Yang
1
, Xiushu Qie
1
, Lihua Zhong
1,2
, Qijia He
3
, Gaopeng Lu
4
, Zhichao Wang
5
,
Yu Wang
6
, Ningyu Liu
7
, Feifan Liu
4
, Kang‐Ming Peng
4
, Baoyou Zhu
4
, Anjin Huang
1
,
Mitsuteru Sato
8
, Huien Pan
9
, and Hualong Li
10
1
Key Laboratory of Middle Atmosphere and Global Environment Observation (LAGEO), Institute of Atmospheric
Physics, Chinese Academy of Sciences, Beijing, China,
2
School of Atmospheric Sciences, Chengdu University of
Information Technology, Chengdu, China,
3
Chongqing Air Traffic Control Branch of Southwest Regional Air Traffic
Administration of Civil Aviation of China, Chongqing, China,
4
School of Earth and Space Science, University of Science
and Technology of China, Hefei, China,
5
China Meteorological Administration, Beijing, China,
6
State Grid Electric Power
Research Institute, Wuhan, China,
7
Space Science Center, Department of Physics, University of New Hampshire,
Durham, NH, USA,
8
Department of Cosmosciences, Hokkaido University, Sapporo, Japan,
9
Xinfeng Culture, Broadcast,
Television, Tourism and Sports Bureau, Shaoguan, China,
10
Finance Bureau of Jiahe County, Hunan Province, Chenzhou,
China
Abstract At about 22:43:30 BJT (Beijing Time = UTC + 8) on 13 August 2016, two amateur astronomers
in Shikengkong, Guangdong province, and Jiahe County, Hunan province, respectively, fortuitously
captured a gigantic jet (GJ) event simultaneously, and the GJ exact location could be triangulated. The
parent thunderstorm was in a very humid environment (Precipitable Water [PWAT] in excess of 60 mm),
featuring high convective available potential energy (CAPE of 2,428 J/kg). The GJ occurred in the region
with the coldest cloud top brightness temperature of −64 °C, suggesting the GJ was associated with strong
vertical development of the thunderstorm. The vertical cross sections of radar reflectivity also show that the
GJ occurred near the thunderstorm strong convection region (overshooting top). The negative cloud‐to‐
ground flashes dominated during the thunderstorm evolution. Three positive narrow bipolar events (NBEs)
were detected within 30 s before and after the GJ. It indicates that the NBEs were occurred in the upper and
middle layers of the thunderstorm (altitude of 11–13 km) with radar reflectivity of 30–35 dBZ.
1. Introduction
The upward electrical discharges, as one type of transient luminous events (TLEs) (Liu et al., 2015), are clas-
sified by their top altitudes: blue starters (20–30 km) (Wescott et al., 1996, 2001), blue jets (40–50 km) (Lyons
et al., 2003; Wescott et al., 1995, 1998, 2001), and gigantic jets (GJs) (70–90 km) (Boggs et al., 2018, 2019;
Cummer et al., 2009; He et al., 2019; Kuo et al., 2009; Peng et al., 2018; Su et al., 2003; Van der Velde et al.,
2007, 2010; Yang & Feng, 2012; Yang etal., 2018). GJs have the largest vertical extension in the upward elec-
trical discharge group that starts from the thunderclouds and propagate upward to the lower ionosphere.
The GJ established a direct path of an electrical connection between the cloud top and the ionosphere
(Cummer et al., 2009; Kuo et al., 2009), which has an important influence on the electron density and poten-
tial of the ionosphere, electromagnetic environment of the near space, and radio communication. Since the
first GJ was observed on 14 September 2001 by Pasko et al. (2002) in Puerto Rico, several GJs have been
observed by ground‐based (Cummer et al., 2009; He et al., 2019; Lu et al., 2011; Peng et al., 2018; Soula
et al., 2011; Su et al., 2003; Van der Velde et al., 2007, 2010, 2019) and satellite‐based experiments (Boggs
et al., 2019; Chen et al., 2008; Kuo et al., 2009). Optical observations show that most of the observed GJs have
“tree”or “carrot”shape (Liu et al., 2015; Pasko et al., 2002; Soula et al., 2011; Su et al., 2003) and there is a
color transition zone between the two areas where the bottom (altitude 20–40 km) is blue and the top (alti-
tude over 65 km) is red (Peng et al., 2018; Soula et al., 2011).
Past studies show that GJ's parent thunderstorms present diversity and were associated with tall summer
thunderstorm cells (Meyer et al., 2013; Pasko et al., 2002; Su et al., 2003), high precipitation supercell
(Van der Velde et al., 2007), multicell thunderstorm (Van der Velde et al., 2007), tropical thunderstorm
©2020. American Geophysical Union.
All Rights Reserved.
RESEARCH ARTICLE
10.1029/2019JD031538
Key Points:
•The location of a gigantic jet was
triangulated using photographs
•The jet occurred just after the peak
of a convective pulse
•Three narrow bipolar events
clustered around the jet time
Correspondence to:
X. Qie,
qiex@mail.iap.ac.cn
Citation:
Yang, J., Qie, X., Zhong, L., He, Q., Lu,
G., Wang, Z., et al. (2020). Analysis of a
gigantic jet in southern China:
Morphology, meteorology, storm
evolution, lightning, and narrow
bipolar events. Journal of Geophysical
Research: Atmospheres,125,
e2019JD031538. https://doi.org/
10.1029/2019JD031538
Received 21 AUG 2019
Accepted 24 JUN 2020
Accepted article online 29 JUN 2020
YANG ET AL. 1of14
(Boggs et al., 2019; Cummer et al., 2009; Lu et al., 2011). Additionally, GJs can also occur in the
thunderstorm belt of hurricanes or typhoons (Cummer et al., 2009), containing embedded mini‐
supercells. However, GJ can also be produced by winter thunderstorms with low CAPE of 300 J/kg and
the cloud top height of only 6.5 km as reported by Van der Velde et al. (2010). In addition, lightning
activity in the parent thunderstorms of the GJs was also diverse. Van der Velde et al. (2010) found that
the storm was positive cloud‐to‐ground (CG) flashes dominated but there was a very low rate from about
30 min before the time of the GJ. The results from Yang and Feng (2012) demonstrated that −CG
(negative CG flashes) dominated during a time window containing the GJ in a summer type
thunderstorm. In contrast, Soula et al. (2011) and Peng et al. (2018) found that no CG flashes were
associated with the occurrence of the GJs. As for the formation mechanism of GJs, Lu et al. (2011) suggest
that narrow bipolar events (NBEs) may be the initial events in the process of GJs. The NBEs are a very
short‐lasting, special kind of intracloud discharge. However, NBEs were only found in Lu et al. (2011) and
Liu et al. (2015).
Previous studies have provided ample insights into the GJs. However, the characteristics of the GJ, its asso-
ciated thunderstorm, and lightning activity are still hot issues due to the rarity of GJs (global incidence of
0.01 jets per minute) (Chen et al., 2008). Moreover, most ground‐based observed GJs were recorded only
by a single station, and the exact location of the GJs cannot be determined. At about 22:43:30 BJT on 13
August 2016, a GJ event in southern China has been recorded by two amateur astronomers in
Shikengkong, Guangdong Province (24.895°N, 112.966°E), and Jiahe County, Hunan Province (25.595°N,
112.379°E), respectively. The cameras are not GPS synchronized, and the GJ occurrence time given in the
present paper is not very accurate. For the rarity of the GJ and the time of the event are close in
Figures 1a and 1b, the discharge image obtained by the two amateur astronomers is very likely the same,
and we assume that they are the same event. Since the GJ has been captured by two sites, its exact location
can be triangulated. The distance between the GJ and the camera in Guangdong province is the closest
(~30 km) so far. In the present paper, the morphology of the GJ has been analyzed in detail. Meanwhile, a
comprehensive analysis of the meteorological environment, the structure of the parent thunderstorm, and
Figure 1. (a) Image of the GJ, seen in Shikengkong in Ruyuan Yao autonomous county, Qingyuan City, Guangdong
Province, China, 13 August 2016 at approximately 22:43:30 BJT (UTC + 8). Equipment: Canon EOS 6D, Sigma 15 mm
fisheye. Exposure parameters: 10 s, f/2.8, ISO1600. The field view of the camera system is 135° horizontally and 90°
vertically. Image is printed with permission (Huien Pan). (b) Image of the GJ, seen in Jiahe County, Chenzhou City,
Hunan Province, China, 13 August 2016 at approximately 22:43:30 BJT (UTC + 8). Equipment: Nikon D60, Nikon 18–
55 mm. Exposure parameters: 15 s, f/3.5, ISO1600. The image is printed with permission (Hualong Li). The stars Markab,
Enif, Homam, Suudalnujun, and Fomalhaut and Skat are used to establish the azimuth and elevations.
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lightning activity have also been performed by using data from Doppler radar, lightning detection network,
European Centre for Medium‐Range Weather Forecasts (ECMWF) reanalysis, infrared weather maps,
sounding, and magnetic field data. What is interesting is that three NBEs were detected in a time window
containing the GJ, and the characteristics of NBEs were also analyzed. The above results enriched our under-
standing of the GJ and the associated thunderstorms.
2. Data and Measurements
Data used in the present paper include optical images, Doppler weather radar data, lightning detection net-
work data, magnetic field, ECMWF reanalysis, sounding data, and the infrared weather maps of MTSAT
(Multi‐Function Transport Satellite).
The optical images of the GJ are obtained from two amateur astronomers in Shikengkong, Guangdong
Province, and Jiahe County, Hunan Province, respectively. This GJ event has been preliminarily analyzed
by another amateur astronomer, and the results are shown in Figure 1 (https://card.weibo.com/article/m/
show/id/2309404009706455701119). They used the following method to triangulate the GJ: First, analyze
the background stars in Figure 1, and find the azimuth and vertical angles of the GJ relative to
Shikengkong and Jiahe. The intersection point (the location of the GJ) of the line of sight of two amateur
astronomers on the map is calculated by the azimuth angles. The distances between the GJ location and
the observers can be obtained by simple calculations. The field of view (FOV), the location and altitude of
the camera, the radius of the Earth (6,378 km) are all known. With all the information above are known
and assuming that the GJ is vertical and perpendicular to the ground, the GJ vertical extension can be cal-
culated by using a geometric method, for example, in Yang et al. (2008). We will use this result for further
analysis.
The ECMWF reanalysis is the global grid point data obtained by assimilating ground observations, sounding
balloon observations, satellite inversion, and other data. It is considered to be basically credible and widely
used all over the world. In this paper, ECMWF reanalysis data (http://apps.ecmwf.int/datasets/data/
interim-full-daily/levtype=pl/) are used to analyze the meteorological environment of the GJ parent thun-
derstorm. The resolution is 0.125° × 0.125°.
The atmospheric sounding data have been downloaded from the University of Wyoming (weather.uwyo.
edu/upperair/sounding.html). The data are provided twice daily at 00:00 and 12:00 UTC
(BJT = UTC + 8), and the time used in the present paper is BJT except noted. The sounding station that
is close to the GJ location is Qingyuan Station (23.6820°N, 113.0561°E, Station Number 59280). The cloud
top brightness temperature is obtained from the MTSAT (Multi‐Function Transport Satellite) satellite obser-
vations, and the data are downloaded online (from http://weather.is.kochi-u.ac.jp/archive-e.html). The data
were updated every hour, and the spatial resolution is 0.05° × 0.05°. Data from the S‐band WSR‐98D fully
coherent Doppler weather radar located in Guangzhou (24.7908°N, 113.5658°E) are used to obtain more
detailed information of the thunderstorm. The radar data are updated every 6 min with a scanning range
of 230 km and its spatial resolution of 1 km. The location and peak current of CG flashes are given by
Guangdong lightning detection network operated by the State Grid Electric Power Research Institute. The
detection efficiency and location error of the network are 92% and 760 m, respectively (Zhang et al., 2014),
which is obtained by using artificially triggering lightning with known ground striking points. The electric
field data are provided by Jianghuai Area Sferic Array (JASA). JASA is a lightning location network, which
consists of six stations. Each station is equipped with a very low frequency (VLF)/low frequency (LF) detec-
tor that consists of a vertical E‐field antenna and two orthogonal magnetic field frame antennas (Liu
et al., 2018).
3. Analysis of GJ Images
The optical images of the GJ obtained in Shikengkong (Ruyuan Yao autonomous county) and Jiahe county
are shown in Figures 1a and 1b, respectively. Figure 1a is the clearest optical image of the GJ recorded from
ground‐based observations so far. Although the upward propagating feature could not be obtained from the
static image, it shows clearly that the GJ connected with the thundercloud top, confirming the observations
of previous studies (Soula et al., 2011). Figure 1a indicates there is a color transition region between the
lower and upper part of the GJ, and the lower part is in blue while the upper part is in red. The top part
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of the GJ in Figure 1a was much darker than the lower part; thus, it was not obvious on the image as the
lower part. Only the part connected with the cloud top at the bottom of the GJ can be clearly seen in
Figure 1b. Van der Velde et al. (2007) explained this is due to the much shorter duration of the upper jet
compared to the lower jet. The relative durations can be seen very well in Van der Velde et al. (2019).
Another reason is likely that at f/3.5, ISO1600, and 15 s exposure time, the background light overwhelms
the little light emitted by the GJ during just a few hundred milliseconds.
Due to the long exposure time, the fine structure of GJ cannot be seen. The GJs reported by Peng et al. (2018)
and Soula et al. (2011) have low luminosity and color image; the fine structure of GJ can be seen in low
luminosity image but not in color image. From the analysis results in Figure 1a, it can be seen that the initial
altitude of GJ is about 20 km, but according to the initiating point of the GJ images taken in Guangdong, it is
blocked by clouds due to the close distance and high elevation angle. Therefore, we will use the radar data for
further analysis in Part 5.
4. Meteorological Environment
Figures 2a and 2b show 500 hPa geopotential height, wind, and temperature and 850 hPa geopotential
height, wind, and water vapor flux at 20:00 BJT on August 13, 2016, respectively. The results show that there
was an upper trough on 500 hPa near 117°E and Guangdong Province was located in the front of the upper
trough. The Pseudo‐Equivalent potential temperature was high from the ground to 800 hPa at 22–28°N in
Figure 2c, and a large amount of unstable energy was accumulated in the lower atmosphere. The results
Figure 2. (a) 500 hPa geopotential height (black contours, unit: gpdam), wind (black arrow, unit: M/s), and temperature (shaded, unit: °C); (b) 850 hPa
geopotential height (black contours, unit: Gpdam), wind (black arrow, unit: M/s), and vapor flux (shaded, unit: g·cm
−1
·hPa
−1
·s
−1
); (c) vertical profile of
pseudo‐equivalent potential temperature along 113.324°E of GJ (unit: K); (d) vertical profile of divergence along 24.835°N of GJ (unit:10
−5
s
−1
) at 20:00 BJT on 13
August 2016. The square box in (a) and (b) represents the region of interest, and the red “+”represents the location of GJ.
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of Qingyuan sounding at 20:00 BJT (Table 1) also show the Lifted
Index (LI) was −5.78 °C, indicating that a large amount of unstable
energy was accumulated in the region of interest.
Figure 2b shows there is a distinct transport belt of water vapor on
850 hPa and the center of the large value of vapor flux was controlled
by the westerly wind, which is conducive to continuous water trans-
port to Guangdong Province located in the northeast of the belt.
Distribution of vapor flux divergence at 850 hPa shows that most
regions in Guangdong Province were located in the convergence zone of water vapor flux, which provides
favorable water vapor conditions for the occurrence and development of the thunderstorm. The vertical pro-
file of divergence along 24.835°N where the GJ was located is shown in Figure 2d. The results indicate a
divergence and convergence center at 200 and 900 hPa, respectively, forming favorable conditions for con-
vergence in the lower atmosphere and divergence in the upper atmosphere. The upward motion caused
by the strong divergence in the middle and upper levels provided dynamic conditions for the development
of a thunderstorm.
The T‐logpdiagram from Qingyuan (within 200 km of the GJ parent thunderstorm) at 20:00 BJT 13 August
2016 (Figure 3) shows that the temperature dew point difference was small below 500 hPa, indicating that
relative humidity was high while the large temperature dewpoint difference above 500 hPa was indicative
of low relative humidity. The wind rose diagram in the upper right corner of Figure 3 shows that there
was a large wind shear in the middle and upper level (12 m/s between 400 and 200 hPa). The shear between
the central charge center and upper charge or even the cloud top may be important for the GJ (Krehbiel
et al., 2008; Lazarus et al., 2015; Van der Velde et al., 2010).
Some key environmental parameters obtained from Qingyuan sounding at 20:00 BJT are listed in Table 1.
The CAPE value was high of 2,428 J/kg, and K index was −42.5 °C, which indicates that the atmosphere
is unstable. The 0 °C height was 5.3 km, and the PWAT (precipitable water) was over 60 mm. Overall, the
atmospheric environment was very moist and featured tropical characteristics.
5. Characteristics of the
GJ‐Producing Thunderstorm
5.1. Overall Characteristic of the Thunderstorm
The radar composite reflectivity images in Figure 4 show that the
storm began with several small convective cells (named S1) that
appeared at about 15:00 BJT on 13 August 2016 near Shaoguan,
which then merged and reached a maximum radar reflectivity of 52
dBZ at 18:24 BJT with the coldest cloud top brightness temperature
of −66°C at 18:24 BJT (Figure 4c). Meanwhile, a new small storm cell
(the GJ‐producing thunderstorm, named S2) occurred northeast of
S1. Then, thunderstorm S1 gradually weakened and almost disap-
peared at 21:00 BJT. S2 moved westward and developed rapidly after
20:00 BJT with the coldest cloud top brightness temperature of −64°C
(Figure 5a) and the maximum radar reflectivity of 57 dBZ at 22:42
BJT (Figure 4e). The GJ occurred at 22:43 during the maturity stage
of the thunderstorm. After the GJ occurrence, the parent thunder-
storm (S2) began to weaken and disappeared completely at 03:00
BJT on August 14. As seen in Figure 4e, the GJ occurred in the area
where the radar composite reflectivity was between 40 and 45 dBZ.
5.2. Thunderstorm Structure
Figure 5a shows cloud top brightness temperature at 23:00 BJT with
lightning activity 3 min before the GJ. The results show that the cold-
est brightness temperature region corresponded very well with the
convection region in the GJ‐producing thunderstorm (S2)
Table 1
The Meteorological Parameters of the Background Environment of the GJ
Parent Thunderstorm
Station
LI
(°C)
CAPE
(J/kg)
PWAT
(mm)
0°C
height
(km)
0–6km
shear (m/s)
K index
(°C)
Qingyuan −5.7 2,428 66.3 5.3 4.6 42.5
Figure 3. Upper air sounding (skew T‐logp) temperature (°C, the blue line),
dewpoint (°C, the red line), parcel adiabatic lapse rate (the black line in the
right), and wind (kt) obtained from Qingyuan sounding at 20:00 BJT on 13
August 2016. The circular diagram in the upper right corner is a wind rose
diagram.
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(Figure 4e). The GJ location was marked by cyan “×”in Figure 5a and was located in the area of the lowest
cloud top brightness temperature with −64°C, which was consistent with the previous results (Boggs
et al., 2019; Singh et al., 2017; Soula et al., 2011).
The cloud top temperature determined from MTSAT satellite gives an estimation of the cloud top altitude,
and the coldest temperature indicates the highest altitude (Soula et al., 2009). The previous results indicate
that the GJ location was most likely related to the coldest cloud top temperature; that is, the occurrence of GJ
may be related to the vertical development of thundercloud (He et al., 2019). Figure 5b depicts the area
Figure 4. Radar composite reflectivity images at different times on 13–14 August 2016. The black “×”in panel (e) stands
for the location of GJ.
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evolution of cloud top brightness temperature of the GJ‐producing thunderstorm (S2) from 19:00–24:00 BJT.
According to the Qingyuan sounding at 20:00 BJT, the temperature of −55°C was at about 13 km altitude.
The area of cloud top brightness temperature colder than −55°C (altitudes above 13 km) continued to
increase until 20:00 BJT. After 20:00 BJT, the area of these temperature intervals began to decrease.
However, the area of the whole system constantly increased until 23:00 BJT. We also noticed that the
coldest cloud top brightness temperature (temperature below −60°C) reappeared at 23:00 BJT (the closest
time to the occurrence of the GJ), indicating the strong vertical development in GJ parent thunderstorm.
Overall, the GJ appeared in the mature stage of the thunderstorm, which is different from the GJ reported
by Soula et al. (2011) and Meyer et al. (2013). The thunderstorm began to weaken and dissipated
gradually after the occurrence of GJ. The production of GJ was associated with the coldest cloud top
brightest temperature (the highest cloud top), which is consistent with previous reports (He et al., 2019;
Meyer et al., 2013; Van der Velde et al., 2010).
In order to clearly show the thunderstorm characteristics, the radar composite reflectivity and vertical cross
sections along the line of sight of two amateur astronomers are shown in Figure 6. The pink dotted lines AB
and CD represent the line of sight of the observers at Jiahe and Shikengkong, and the intersection of the two
lines is the location of GJ. Cummer et al. (2009) and Van der Velde et al. (2007, 2010) estimated the position
where the radar reflectivity of the azimuth crossed by the GJ was the strongest position for the occurrence of
GJ. Figure 6g shows that the GJ was located near the strongest radar reflectivity, which is similar to the pre-
vious results. The location of GJ in the present paper was obtained by triangulation, which is more accurate
than the result estimated by single station observation to a certain extent. It can be seen that the GJ did not
necessarily occur at the position with the strongest radar reflectivity.
Previous studies show that most GJs are associated with overshooting tops of the thundercloud (He
et al., 2019; Meyer et al., 2013; Peng et al., 2018; Van der Velde et al., 2007). We use the ECMWF reanalysis
data to calculate the tropopause height. The results show that the tropopause height in the thunderstorm
area was about 15.6 km at 20:00 BJT, and the monthly average tropopause height in this area was about
15.7 km in August 2016. The vertical cross sections shown in Figure 6 suggest that the thunderstorm region
close to the GJ in time interval of 22:30–22:42 BJT had strong convection and over shooting tops, indicated
by Figure 6c in which the reflectivity of 25 dBZ reached 18 km and 35 dBZ echo top (ET) also reached 16 km
that exceeded the tropopause (15.6 km, as shown by the black horizontal line in the figure). The results
above indicate that the GJ occurred in close proximity to the strong convective zone in the thunderstorm,
which is consistent with the previous reports (Cummer et al., 2009; Huang et al., 2012; Lazarus et al., 2015;
Su et al., 2003). After the occurrence of GJ (22:48 BJT), the ET fell below 15.6 km, and the thunderstorm
decreased gradually. The cloud top reported by Boggs et al. (2018) was 15 km, which is lower than the results
of the present study.
Figure 5. (a) Cloud top brightness temperature of the GJ‐producing thunderstorm (S2) at 23:00 BJT on 13 August. The
black “.”and rose‐red “+”stand for −CG strokes and +CG strokes, respectively. The GJ location was marked by cyan
“×”. (b) Area evolution of MTSAT cloud top brightness temperature of the GJ‐producing thunderstorm (S2) at different
temperature intervals during 19:00–24:00 BJT.
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Figure 6. The radar composite reflectivity and the vertical section along the lines AB and CD at different times. The vertical section along line AB is shown in
panels (b), (e), (h), and (k); the vertical section along line CD is shown in panel (c), (f), (i), and (l). The black horizontal line in the figure represents the local
tropopause height (~15.6 km).
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Quantitative analysis of radar data can help understanding of the thunderstorm. ETs indirectly reflect the
strong vertical updraft in a thunderstorm. The area evolution of different ET of the GJ‐producing storm is
shown in Figure 7a. The results show that the ET area of 10–14 km altitude increased rapidly before the
GJ, indicating the convection strengthened around this time. Vertically integrated liquid (VIL) indicates
atmospheric water content and precipitation that weather radar can measure. Figure 7b shows the evolution
of maximum VIL of the GJ‐producing thunderstorm. The maximum value of VIL decreased sharply 30 min
before the GJ, suggesting the liquid water content in the cloud decreased.
In addition, we also quantitatively analyze the radar composite reflectivity of the GJ‐producing thunder-
storm (Figure 7c). The results show that the area of 45–50 dBZ increased, while the area of 30–35 and 35–
40 dBZ decreased during the time window containing GJ. The above results indicate that GJ occurrence
was associated with strong reflectivity.
5.3. Characteristics of the Lightning Activity
Detailed analysis of the lightning activity of the parent thunderstorm has been made, and the results are
shown in Figure 8a. The results show that −CG flashes dominated from 20:00–24:00 BJT. The peak value
of −CG flashes occurred between 22:00 and 23:00 BJT, and the number of −CG flashes was about twice that
of +CG flashes. The parent thunderstorm was in its development‐maturation stage during that time period.
After 23:00, both −CG and +CG flashes activity decreased, suggesting the parent thunderstorm was
dissipating.
Figure 8b shows the cumulative flash rates within ±0.25° centered at the GJ location. It shows −CG and
+CG flash rates of on average 8 and 6.5 min
−1
, respectively. Negative CG flashes almost ceased during a
Figure 7. Area evolution of (a) different echo tops (ET), (b) maximum vertically integrated liquid (VIL), and (c) different
composite reflectivity in ±0.5° range of GJ during 22:12–23:12 BJT.
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short period (22:41–22:42 BJT), while positive CG flashes increased (16 +CG flashes). Negative CG flashes
increased, and positive CG flashes decreased 1 min before the GJ. The CG flashes continued to decrease
after the GJ. The results of Krehbiel et al. (2008) and Riousset et al. (2010) show that there is a
competitive relationship between the GJ and CG flashes, the charges needed to generate them come from
the same charge source in the cloud, and the charges transferred by the GJ were very large (Cummer
et al., 2009; Lu et al., 2011; Liu et al., 2015). Thus, the sharp decrease of CG flashes may suggest the
accumulation of charges in the cloud and provides enough charge and energy for the generation of GJs.
The change of positive and negative CG flashes rate before and after the GJ may provide some
information for the charge accumulation during the occurrence of GJ. However, since the polarity of the
GJ in this study is unknown and there is no other observation to prove the charge structure in the cloud,
so further study is needed.
Figure 8c shows the peak currents of the positive and negative CG flashes within ±0.5° centered at the GJ
location. A total of 1,227 CG flashes were detected within 30 min before and after the GJ, including 759
−CG flashes (about 62%) with the maximum peak current of −174.1 kA, and 468 +CG flashes (about
38%) with the maximum peak current of +159 kA. Before and after the GJ, the average of peak current of
+CG and −CG was +29.3 kA (+26.4 kA) and −11.27 kA (−25.8 kA), respectively. It can be seen that the
average peak current of +CG did not change much before and after the GJ (+29.3 to +26.4 kA), while the
average peak current of −CG was about twice that before the GJ. Based on the results of Krehbiel et al. (2008),
negative GJ and −CG have similar charge structure layers in storms. The average peak current of −CG was
small before the GJ, indicating that more negative charge accumulated in the clouds and more negative
Figure 8. (a) Evolution of CG flashes per 6 min in the parent thunderstorm (S2), (b) cumulative flash rates within ±0.25°
centered at the GJ, location, and (c) evolution of peak current of CG flashes in the GJ parent thunderstorm (S2) within
±0.5° centered at the GJ location. The vertical black lines in (a), (b), and (b) represent the time of GJ occurrence. The
horizontal blue dotted line in panel (c) represents the value of +15 kA.
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charge was released after the GJ. The above results are only derived from the average peak currents of −CG
and +CG, and further studies are needed in the future.
6. Possible Relationship Between GJ and NBE
NBEs are one type of in‐cloud discharge process with relatively short timescale (typically about 10–20 μs)
(Smith et al., 1999). NBEs produce extremely powerful natural radio frequency radiation (Rison et al.,
2016; Smith et al., 1999; Zhu et al., 2010). By analyzing the data obtained by Guangzhou Meteorological
Administration, we fortuitously found 11 cases of NBEs during the thunderstorm lifecycle. Among the 11
cases of NBEs, three NBEs were detected within 30 s (22:43:00–22:44:00 BJT) before and after the GJ.
Figure 9 shows the waveforms of three NBEs, and it indicates that all the three NBEs in this study were of
positive polarity. The characteristics of the bipolar pulse waveforms were consistent with the results reported
by Wu et al. (2012). The pulse 0 was generated when the observation station received the wave signal of the
NBE (ground wave), and the pulses a and b (reflected wave) were the signals that are reflected by the iono-
sphere and the ground ionosphere, respectively. The time, location, and electric field strength of the NBEs
are given in Table 2. Lu et al. (2011) reported that NBE is likely to be the initial event of a GJ. However,
the occurrence time of the GJ cannot be determined exactly, so the correlation between NBE and the GJ can-
not be further studied in this study and need to be completed by other observations.
The result showed that positive NBEs occurred between the upper main positive charge region and the mid-
level main negative charge region in the tripole electrical structure of thunderstorm (Rison et al., 1999; Wu
et al., 2011), mainly starting at 8–15 km, with an average height of 12.8 km. It occurred as the initiating event
of intracloud lightning discharges. Negative NBE occurred between the upper main positive charge region
and the negative screening charge region (Smith et al., 1999; Wu et al., 2012), starting at 15–19 km, with
Figure 9. The electric field waveform of three positive NBEs detected within 30 s before and after the GJ. (a) 22:43:00
BJT; (b) 22:43:13 BJT; and (c) 22:43:54 BJT.
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an average height of about 16.4 km. The method for calculating the
source height of NBE in the present study is similar to that used by
Wu et al. (2012). The basic principle is to determine the source height
by using the time delay between the original signal (ground wave) of
an NBE and its ionosphere and ground reflection signal (reflected
wave). Suppose his the source height of NBE, His the height of iono-
spheric reflection, t
a
is the time difference between pulses a and 0,
and t
b
is the time difference between pulses b and 0, using geometric
relation to get the following equation:
cta−ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2H−hðÞ
2
q−ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
h2þr2
p
¼0;(1)
ctb−ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2Hþh2þr2
p−ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
h2þr2
p¼0;(2)
where ris the spherical distance between sensor location (lon0, lat0) and NBE source location (lon1, lat1):
r¼R· arccos sin lat1ðÞsin lat0ðÞþcos lon1ðÞcos lat0ðÞcos lon1ðÞ−lon0½;(3)
where Ris the Earth radius. Therefore, according to the longitude and latitude of NBE events provided by
the network and the time delay of reflected and ground waves, the source height of NBE can be calculated
by combining functions (1) and (2).
According to Equations 1 and 2, the height of three positive NBEs is calculated to be 11–13 km as shown in
Table 2, with an average altitude of 12.2 km. Smith et al. (1999) found that NBE tended to occur in the per-
ipheral region of high radar reflectivity. Figure 10a shows overlaps of radar composite reflectivity at 22:42
BJT with NBEs. Three positive NBEs were located in the periphery of the strong echo region with radar
reflectivity of 45–50 dBZ. In order to explore the relationship between the source height of positive NBE
and the charge structure corresponding to the thunderstorm area, overlap of the vertical section along line
AB in Figure 10a with NBE is shown in Figure 10b. The results show that positive NBEs were located in the
middle and upper regions of the thunderstorm and occurred in the region with reflectivity of 30–35 dBZ,
which is similar to the results of Lü et al. (2013).
7. Conclusions
One GJ event captured over a thunderstorm in south China at about 22:43:30 BJT on 13 August 2016 is
reported in this paper. The triangulation of the GJ was obtained through the synchronous observation from
Table 2
Information on the Three Positive NBEs on 13 August 2016
Time (BJT) Location Height (km) E (V/m) Location error
22:43:00 24.80°N, 113.36°E 12.8 450 <500 m
22:43:13 24.79°N, 113.40°E 11.4 135 <500 m
22:43:54 24.91°N, 113.37°E 12.5 298 <500 m
Figure 10. (a) Overlapped image of three positive NBEs generated between 22:43 and 22:44 BJT on 13 August 2016 with
the radar composite reflectivity at 22:42 BJT. (b) Vertical cross section along line AB. The positive NBEs are marked by
black “×,”the blue “+”shows the location of GJ.
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two amateur astronomers in Shikengkong, Guangdong Province, and Jiahe County, Hunan Province,
respectively. We analyzed the meteorological background environment, characteristics of the parent thun-
derstorm, and lightning activity by using multiple data. In addition, three interesting NBEs have been found
in a time window containing the GJ, and the characteristics of NBEs were also analyzed. The main results
obtained from our analysis are summarized as follows:
1. The GJ parent thunderstorm was in a very humid environment (PWAT greater than 60 mm) with high
CAPE (2,428 J/kg) and weak 0–6 km vertical wind shear (4.6 m/s). The area of coldest cloud top bright-
ness temperature (below −60°C) appeared at the nearest to the occurrence of GJ, suggesting the GJ was
associated with strong vertical development of the thunderstorm.
2. There was an indication of the overshooting top in the parent thunderstorm near the time of GJ, which
reveals the existence of strong convection in the cloud. Quantitative analysis of radar reflectivity showed
that before the GJ initiation, the ET area of 10–14 km altitude increased rapidly, indicating the convec-
tion enhanced around this time.
3. Analysis of lightning activity showed that the thunderstorm was dominated by −CG flashes. A total of
1,227 CG flashes were detected within 30 min before and after the GJ, including 759 −CG flashes (about
62%) with the maximum peak current of −174.1 kA, and 468 CG flashes (about 38%) with the maximum
peak current of +159 kA.
4. Three positive NBEs were detected within the 30 s before and after the GJ. It indicates that the NBEs were
distributed between the positive and negative charge region (11–13 km). The relationship between NBE
and thunderstorm macrometeorology has the following characteristics: three positive NBEs were located
in the periphery of the strong echo region with radar reflectivity of 45–50 dBZ and occurred in the upper
and middle layers of a thunderstorm with radar reflectivity of 30–35 dBZ.
Data Availability Statements
The optical images of the gigantic jet are available online (from the link https://zenodo.org/record/
3734288#.XoMqfLB0yUk).
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Acknowledgments
This work was supported jointly by the
Strategic Priority Research Program of
the Chinese Academy of Sciences
(Grant XDA17010101) and the National
Natural Science Foundation of China
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