During July 1966, nearly 100 tetroon flights were made at the National Reactor Testing Station (NRTS), Idaho Falls, with the primary purpose of verifying the existence of longitudinal roll-vortices, or helices, in the planetary boundary layer. The transponder-equipped constant volume ballons (tetroons) were ballasted to float 300 m above the ground and were tracked by two M-33 radars. One radar tracked two tetroons released simultaneously from sites 500 m apart (in a direction normal to the mean flow) and the other radar tracked two tetroons released simultaneously from the same sites about one-half hour later. In the flat, desert-like region of NRTS, there is evidence that counter-rotating helices of about 2 km diameter frequently exist during the afternoon. Basically, the helical motion appears to be one of solid rotation, with an average absolute value for the vorticity in the transverse plane of 4 × 10−3 sec−1, a magnitude similar to that derived from the vertical shear of the longitudinal wi... Abstract During July 1966, nearly 100 tetroon flights were made at the National Reactor Testing Station (NRTS), Idaho Falls, with the primary purpose of verifying the existence of longitudinal roll-vortices, or helices, in the planetary boundary layer. The transponder-equipped constant volume ballons (tetroons) were ballasted to float 300 m above the ground and were tracked by two M-33 radars. One radar tracked two tetroons released simultaneously from sites 500 m apart (in a direction normal to the mean flow) and the other radar tracked two tetroons released simultaneously from the same sites about one-half hour later. In the flat, desert-like region of NRTS, there is evidence that counter-rotating helices of about 2 km diameter frequently exist during the afternoon. Basically, the helical motion appears to be one of solid rotation, with an average absolute value for the vorticity in the transverse plane of 4 × 10−3 sec−1, a magnitude similar to that derived from the vertical shear of the longitudinal wi...