4:15 PM - 4:30 PM
[AAS04-09] Photogrammetric estimation of velocity field around Tsukuba tornado
Keywords:tornado, Particle Image velocimetry, Debris cloud, Funnel cloud
Tornado is one of the most severe meteorological events. Its scale is however very small and its lifetime is very short. Therefore, ordinary instruments cannot measure tornado structure in detail. Especially, it is difficult to measure the tornado structure near ground due to ground clutter even by a high-resolution weather radar. On the other hand, recent digital movies of tornadoes have high spatiotemporal resolution.
The present study aims to measure the tornado structure near ground by using photogrammetric method. Target is Tsukuba tornado occurred afternoon on May 6, 2012. The Fujita scale of this tornado is F3, which shows that it is the most severe tornado in Japan. Many videos of this tornado were taken from various locations. We analyzed three videos with particle image velocimetry. The correction of camera shake, the distance between camera and target tornado and moving speed of tornado itself were also made.
The tangential velocities of debris cloud near ground were estimated to be 30 to 60 m/s. Maximum speeds of gust wind due to the tornado were 56 to 76 m/s. These values correspond with Fujita scale estimated from the damage in the observed point. The conversion flow is also observed near ground as shown in Figure. Its velocity is 34 m/s which is about half of tangential velocity of debris cloud. The velocity at funnel cloud is also estimated. The tangential velocity and updraft velocity are 53 m/s and 4 m/s, respectively. This fact shows that this tornado has very large swirl ratio. Conclusively, photogrammetric analysis of movies is very effective tool to investigate the features of tornadoes in detail.
The present study aims to measure the tornado structure near ground by using photogrammetric method. Target is Tsukuba tornado occurred afternoon on May 6, 2012. The Fujita scale of this tornado is F3, which shows that it is the most severe tornado in Japan. Many videos of this tornado were taken from various locations. We analyzed three videos with particle image velocimetry. The correction of camera shake, the distance between camera and target tornado and moving speed of tornado itself were also made.
The tangential velocities of debris cloud near ground were estimated to be 30 to 60 m/s. Maximum speeds of gust wind due to the tornado were 56 to 76 m/s. These values correspond with Fujita scale estimated from the damage in the observed point. The conversion flow is also observed near ground as shown in Figure. Its velocity is 34 m/s which is about half of tangential velocity of debris cloud. The velocity at funnel cloud is also estimated. The tangential velocity and updraft velocity are 53 m/s and 4 m/s, respectively. This fact shows that this tornado has very large swirl ratio. Conclusively, photogrammetric analysis of movies is very effective tool to investigate the features of tornadoes in detail.