Two‐beam observations of ionospheric irregularity structure and velocity at Arecibo

A new technique has been developed for measuring irregularity structure and velocity in the ionospheric E and F regions. The Arecibo incoherent‐scatter radar was modified to measure electron‐density profiles simultaneously with two beams: one fixed beam pointed at the zenith, and a second beam could be varied over 360° in azimuth and from 2 to 20° in zenith angle. Fluctuations in ionization density were observed to drift from one beam to the other so that information was obtained about both the horizontal velocity and the structure of these disturbances. Velocities of 100 to 200 m sec −1 and horizontal scale sizes of 50 to 100 km were deduced for the E region and roughly 400 m sec −1 and 500 km for the F region. A plot of velocity versus altitude shows a spiral structure with a vertical wavelength of 20 to 30 km in the E region.