2:45 PM - 3:00 PM
[AAS08-05] Direction of tornado movement and its relationship with the tropospheric winds
Keywords:Tornado, Supercell, Circular Statistics
A tornado is a violent atmospheric vortex caused by an updraft in a cumulus or cumulonimbus cloud. Tornadoes are generated when atmospheric conditions are extremely unstable, and can cause extensive damage over a narrow band-like area in a short period of time. In order to reduce damage to humans and infrastractures, we discuss the possibility of the tornado track prediction and its related features.
According to Niino et al. (1997), more than half of tornadoes in Japan from 1961 through 1993 moved toward the northeast quadrant. However, since this data was based on visual observations, the reported directions of tornado motions were biased toward 8 directions out of 16. Therefore, using tornado records from the gusty winds database of the Japan Meteorological Agency between 1961 and 2022, this study collects directional data of tornado motions in an objective way and investigates comprehensively the relationship between directions of tornado motions and the large-scale wind field.
First, the direction of tornado movement is calculated from the latitudes and longitudes of the starting and ending points of the damage area. These calculations show that approximately 70% of tornadoes moved toward the northeast quadrant. The preference for the northeastward movement remains nearly similar for the periods of 1961-1993 and 1994-2022. Although JMA changed several times their operation to collect tornado report data during the periods, and we confirm that the predominance is not due to a sampling bias. The directions of tornado movement is concentrated in the northeast quadrant in all seasons, but in summer and fall, the number of tornadoes is most prominent in the north and the east of the 16 directions. Of these, many of the tornadoes that move north are tornadoes associated with typhoons. Furthermore, even if we repeat the analysis for tornadoes that cause damage above a certain level, the preference for the northeast quadrant remains unchanged, and remains in the northward direction due to an increase in the proportion of typhoon-related tornadoes.
Next, the high correlations between the direction of tornado motions and the large-scale wind directions are also consistent with a notion that tornadoes are transported by winds along with cumulonimbus clouds. Meanwhile, the number of tornadoes that deviate from the direction of the wind is asymmetrical, with many tornadoes moving counterclockwise by 0 to 60 degrees relative to the tropospheric wind. Therefore, by predicting the direction of supercell movement following the method proposed by Bunkers et al. (2000), we will quantitatively verify whether the direction of supercell movement and tornado movement corresponds well with each other.
According to Niino et al. (1997), more than half of tornadoes in Japan from 1961 through 1993 moved toward the northeast quadrant. However, since this data was based on visual observations, the reported directions of tornado motions were biased toward 8 directions out of 16. Therefore, using tornado records from the gusty winds database of the Japan Meteorological Agency between 1961 and 2022, this study collects directional data of tornado motions in an objective way and investigates comprehensively the relationship between directions of tornado motions and the large-scale wind field.
First, the direction of tornado movement is calculated from the latitudes and longitudes of the starting and ending points of the damage area. These calculations show that approximately 70% of tornadoes moved toward the northeast quadrant. The preference for the northeastward movement remains nearly similar for the periods of 1961-1993 and 1994-2022. Although JMA changed several times their operation to collect tornado report data during the periods, and we confirm that the predominance is not due to a sampling bias. The directions of tornado movement is concentrated in the northeast quadrant in all seasons, but in summer and fall, the number of tornadoes is most prominent in the north and the east of the 16 directions. Of these, many of the tornadoes that move north are tornadoes associated with typhoons. Furthermore, even if we repeat the analysis for tornadoes that cause damage above a certain level, the preference for the northeast quadrant remains unchanged, and remains in the northward direction due to an increase in the proportion of typhoon-related tornadoes.
Next, the high correlations between the direction of tornado motions and the large-scale wind directions are also consistent with a notion that tornadoes are transported by winds along with cumulonimbus clouds. Meanwhile, the number of tornadoes that deviate from the direction of the wind is asymmetrical, with many tornadoes moving counterclockwise by 0 to 60 degrees relative to the tropospheric wind. Therefore, by predicting the direction of supercell movement following the method proposed by Bunkers et al. (2000), we will quantitatively verify whether the direction of supercell movement and tornado movement corresponds well with each other.