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[O06-P09] Relationship between forms of sprites in winter and meteorological conditions
Keywords:sprite, lightning, meteorological condition
Sprites, a type of TLEs (high-altitude emission phenomena), are known to occur frequently around the Sea of Japan in winter (November to March) and have a variety of forms. Therefore, we decided to elucidate the relationship between the form of sprites and meteorological conditions using data from 185 events and 190 sprites observed from the school from November 16, 2019 to February 27, 2022, in order to investigate the differences in form due to meteorological conditions.
The method was to use motion detection software to detect sprites captured by a high-sensitivity CCD camera, and to identify the point of occurrence of the sprites based on the camera's viewing angle. Next, sprites are classified into four types according to their forms as shown in Figure 1: Column (columnar), Angel (with angel wing-like portions), Carrot (with carrot beard-like portions), and Wishbone Tree (with branching portions) . The relationship between the form of the sprites and meteorological conditions is analyzed using the meteorological conditions at the point of occurrence, infrared cloud images and rain cloud radar images at the time of occurrence.
Figure 2 show that Column sprites account for approximately 70% of the total number of occurrences, and figure 3 shows that about 80% of Wishbone Tree sprites are accompanied by cold fronts and precipitation of 20[mm/h] or more, which indicates that Wishbone Tree sprites are more likely to occur when active thunderclouds are present. It was found that the occurrence conditions of Angel and Wishbone Tree are similar. Figure 4 shows that the humidity at 500[hPa] tends to be high when Wishbone Tree occurs, and that spreading thin clouds are commonly seen when sprites occur. The electric energy required for the development of cumulonimbus clouds was estimated from the degree of development of cumulonimbus clouds based on meteorological conditions, and it is considered that the electric energy required for the development of cumulonimbus clouds is large for Column, Carrot, Angel, and Wishbone Tree, in that order. Clouds at the time of sprite outbreaks are considered to be caused by convective instability due to incipient low-pressure systems generated when westerly wind meandering is severe and pressure troughs become large in winter.
The above results indicate that the electrical energy required to generate winter sprites differs depending on the type of winter sprite, and that the form of winter sprites is affected by the electrical energy possessed by thunderclouds. The model for the generation of winter sprites is based on the development of a trough in the atmospheric pressure and the temperature difference between the upper and lower layers, which cause atmospheric instability, resulting in the formation of cold fronts and thunderclouds. The form of the sprite is determined by the electrical energy of the cloud and the humidity and dust in the sky.
Future tasks include a detailed study of the relationship between the magnitude of electrical energy possessed by clouds and their forms, as well as the development of a winter sprite generation model using specific numerical values to fully elucidate the generation mechanism of sprites.
The method was to use motion detection software to detect sprites captured by a high-sensitivity CCD camera, and to identify the point of occurrence of the sprites based on the camera's viewing angle. Next, sprites are classified into four types according to their forms as shown in Figure 1: Column (columnar), Angel (with angel wing-like portions), Carrot (with carrot beard-like portions), and Wishbone Tree (with branching portions) . The relationship between the form of the sprites and meteorological conditions is analyzed using the meteorological conditions at the point of occurrence, infrared cloud images and rain cloud radar images at the time of occurrence.
Figure 2 show that Column sprites account for approximately 70% of the total number of occurrences, and figure 3 shows that about 80% of Wishbone Tree sprites are accompanied by cold fronts and precipitation of 20[mm/h] or more, which indicates that Wishbone Tree sprites are more likely to occur when active thunderclouds are present. It was found that the occurrence conditions of Angel and Wishbone Tree are similar. Figure 4 shows that the humidity at 500[hPa] tends to be high when Wishbone Tree occurs, and that spreading thin clouds are commonly seen when sprites occur. The electric energy required for the development of cumulonimbus clouds was estimated from the degree of development of cumulonimbus clouds based on meteorological conditions, and it is considered that the electric energy required for the development of cumulonimbus clouds is large for Column, Carrot, Angel, and Wishbone Tree, in that order. Clouds at the time of sprite outbreaks are considered to be caused by convective instability due to incipient low-pressure systems generated when westerly wind meandering is severe and pressure troughs become large in winter.
The above results indicate that the electrical energy required to generate winter sprites differs depending on the type of winter sprite, and that the form of winter sprites is affected by the electrical energy possessed by thunderclouds. The model for the generation of winter sprites is based on the development of a trough in the atmospheric pressure and the temperature difference between the upper and lower layers, which cause atmospheric instability, resulting in the formation of cold fronts and thunderclouds. The form of the sprite is determined by the electrical energy of the cloud and the humidity and dust in the sky.
Future tasks include a detailed study of the relationship between the magnitude of electrical energy possessed by clouds and their forms, as well as the development of a winter sprite generation model using specific numerical values to fully elucidate the generation mechanism of sprites.