Photogrammetric Velocities for the Great Bend, Kansas, Tornado of 30 August 1974: Accelerations and Asymmetries

Abstract

Late in the afternoon of 30 August 1974 a dozen tornadoes were observed over open farming terrain within a 65 km radius of Great Bend, Kans. All but one of the tornadoes traveled mainly toward the southeast; the other tornado moved northeastward and produced damage near Galatia. One of the largest tornadoes occurred about 40 km west?southwest of Great Bend, and high-resolution motion picture films were taken by a news photographer 2.7 km north of the vortex. The vortex was visible as a rotating column of dense dust and small debris particles. Photogrammetric analysis and tracking of debris in the rotating dust column yield velocities as high as 85 m s?1. Maximum measured horizontal wind speeds are 75 m s?1at z≈90 m AGL and maximum rising motions are 60 m s?1at z≈80 m A remarkable dark band of dust, about 35 m high, apparently outlined a major inflow jet of air accelerating into the vortex at low levels from the west-southwest. The dust band has appeared in other tornado photograph (e.g., Kessler, 1972) but its possible importance to the overall flow structure fuss not been emphasized.