1:45 PM - 3:15 PM
[O08-P14] Identification of cumulonimbus clouds with lightning discharge meteorological records on July 13, 2021
Keywords:giant cumulonimbus clouds, overshoots, Transient Luminous Events, high-sensitivity CCD camera
$1. Motivation and Objective
Our school has been studying transient luminous event for a long time. However, the cause of its occurrence is still unknown. Therefore, as a first step to understand the reason for this, this study establishes a method to identify the cumulonimbus cloud with this lightning discharge by using many lightning flashes and meteorological records observed from our school on July 13, 2021. In addition, this study was conducted to elucidate the process of development and decay of cumulonimbus clouds and the causes of their formation.
$2. Hypothesis
The thunderstorm observed on July 13, 2021 was caused by a cumulonimbus cloud that formed on the north side of the school in the early afternoon of the same day.
The cause of the outbreak was a strong updraft within the cumulonimbus cloud.
$3. Method
Lightning captured by the high-sensitivity CCD camera (WAT-100N) is constantly monitored by motion detection software and automatically recorded on a PC. Next, the direction of the lightning is identified based on the camera's viewing angle by extracting only the lightning from the images captured by the school's camera. Furthermore, the locations of thunderstorm-emitting cumulonimbus clouds are identified based on visible and infrared images from meteorological satellites, radar echo images of rain clouds, and time-varying videos of the number of anti-mine incidents from the Blitz anti-mine data. Finally, the development and decay processes of thunderstorms, lightning strikes, and cumulonimbus clouds are investigated by comparing the results with weather maps published by the Japan Meteorological Agency, high-level weather data from AMeDAS and radiosondes.
$4. Results and Discussion
4-1. Direction of observed lightning flashes
Figure 1 shows the observation azimuths of the C1 camera facing northwest, divided into left, center, and right. The observed lightning was more frequent in the center at 19:30, but less frequent at 20:00. Conversely, on the left side, there was less lightning at 19:30, but more at 20:00, indicating that the lightning source was located northwest of the school at 19:00, but moved to the west by 20:00. Figure 2 shows the observation azimuths of the north-facing C2 camera. The observed lightning was highest on the left side at 19:30, followed by the center, and decreased with time. This indicates that the lightning source was located north of the school at 19:00 based on the azimuth angle of the C2 camera, and that it did not change its position and faded with time.
4-2. Identification of Cumulonimbus Clouds with Lightning Discharge
Based on the direction of the lightning source, the cumulonimbus clouds causing the lightning were identified from satellite images, radar echo images, and Blitz anti-mine data. Figure 3 shows the satellite image, and Figure 4 shows the Blitz data against land mines. According to all the data, huge cumulonimbus clouds with overshoots existed over Nagoya City in the western part of Aichi Prefecture in the northwest direction of Camera C1 and over Toei Town in the eastern part of Aichi Prefecture in the north direction of Camera C2 during this time period. The visible image shows that this cumulonimbus cloud is a giant cumulonimbus cloud formed by the merging of a large number of cumulonimbus clouds that occurred around 15:00. An overshoot is a cumulonimbus cloud in which the updrafts in the cloud become so intense that the top of the cloud breaks through the boundary of the sphere and reaches the stratosphere. It is thought that the intense convection in the interior of this cumulonimbus cloud causes the accumulation of enormous electric charge, and the subsequent Electrical breakdown of insulation produces numerous lightning flashes.
4-3. Causes of Giant Cumulonimbus Clouds
The giant cumulonimbus clouds are considered to have formed due to the following reasons.
(1) Rise in surface temperature due to strong solar radiation.
(2) As shown in Figure 5, the supply of moist water vapor from the south flowing into the rainy season front and the strong updrafts generated by the impact of this vapor on the Central and Southern Alps.
(iii) Inflow of cold air into the sky as expected from radiosonde records at Wajima
$5. Conclusion
The cumulonimbus clouds with lightning discharges can be identified as two giant cumulonimbus clouds that developed over Nagoya City and Toei Town in Aichi Prefecture. This giant cumulonimbus cloud was formed by the coalescence of a group of cumulonimbus clouds, and repeated lightning discharges were caused by Erectrical breakdown.
Our school has been studying transient luminous event for a long time. However, the cause of its occurrence is still unknown. Therefore, as a first step to understand the reason for this, this study establishes a method to identify the cumulonimbus cloud with this lightning discharge by using many lightning flashes and meteorological records observed from our school on July 13, 2021. In addition, this study was conducted to elucidate the process of development and decay of cumulonimbus clouds and the causes of their formation.
$2. Hypothesis
The thunderstorm observed on July 13, 2021 was caused by a cumulonimbus cloud that formed on the north side of the school in the early afternoon of the same day.
The cause of the outbreak was a strong updraft within the cumulonimbus cloud.
$3. Method
Lightning captured by the high-sensitivity CCD camera (WAT-100N) is constantly monitored by motion detection software and automatically recorded on a PC. Next, the direction of the lightning is identified based on the camera's viewing angle by extracting only the lightning from the images captured by the school's camera. Furthermore, the locations of thunderstorm-emitting cumulonimbus clouds are identified based on visible and infrared images from meteorological satellites, radar echo images of rain clouds, and time-varying videos of the number of anti-mine incidents from the Blitz anti-mine data. Finally, the development and decay processes of thunderstorms, lightning strikes, and cumulonimbus clouds are investigated by comparing the results with weather maps published by the Japan Meteorological Agency, high-level weather data from AMeDAS and radiosondes.
$4. Results and Discussion
4-1. Direction of observed lightning flashes
Figure 1 shows the observation azimuths of the C1 camera facing northwest, divided into left, center, and right. The observed lightning was more frequent in the center at 19:30, but less frequent at 20:00. Conversely, on the left side, there was less lightning at 19:30, but more at 20:00, indicating that the lightning source was located northwest of the school at 19:00, but moved to the west by 20:00. Figure 2 shows the observation azimuths of the north-facing C2 camera. The observed lightning was highest on the left side at 19:30, followed by the center, and decreased with time. This indicates that the lightning source was located north of the school at 19:00 based on the azimuth angle of the C2 camera, and that it did not change its position and faded with time.
4-2. Identification of Cumulonimbus Clouds with Lightning Discharge
Based on the direction of the lightning source, the cumulonimbus clouds causing the lightning were identified from satellite images, radar echo images, and Blitz anti-mine data. Figure 3 shows the satellite image, and Figure 4 shows the Blitz data against land mines. According to all the data, huge cumulonimbus clouds with overshoots existed over Nagoya City in the western part of Aichi Prefecture in the northwest direction of Camera C1 and over Toei Town in the eastern part of Aichi Prefecture in the north direction of Camera C2 during this time period. The visible image shows that this cumulonimbus cloud is a giant cumulonimbus cloud formed by the merging of a large number of cumulonimbus clouds that occurred around 15:00. An overshoot is a cumulonimbus cloud in which the updrafts in the cloud become so intense that the top of the cloud breaks through the boundary of the sphere and reaches the stratosphere. It is thought that the intense convection in the interior of this cumulonimbus cloud causes the accumulation of enormous electric charge, and the subsequent Electrical breakdown of insulation produces numerous lightning flashes.
4-3. Causes of Giant Cumulonimbus Clouds
The giant cumulonimbus clouds are considered to have formed due to the following reasons.
(1) Rise in surface temperature due to strong solar radiation.
(2) As shown in Figure 5, the supply of moist water vapor from the south flowing into the rainy season front and the strong updrafts generated by the impact of this vapor on the Central and Southern Alps.
(iii) Inflow of cold air into the sky as expected from radiosonde records at Wajima
$5. Conclusion
The cumulonimbus clouds with lightning discharges can be identified as two giant cumulonimbus clouds that developed over Nagoya City and Toei Town in Aichi Prefecture. This giant cumulonimbus cloud was formed by the coalescence of a group of cumulonimbus clouds, and repeated lightning discharges were caused by Erectrical breakdown.