ROLE OF STEEPENED STRUCTURES AND DRIFT WAVES IN EQUATORIAL SPREAD-F

A time domain analysis, performed upon electron density data obtained on the bottomside of the F peak during equatorial spread F conditions, indicates that the observed k** minus **2 wave number spectrum is due to sharp gradients in the medium and not to plasma turbulence. The gradients are then shown to be unstable to drift waves with a peak growth rate of about 1 s** minus **1 which occurs at perpendicular wavelengths near the ion gyroradius. These waves may be responsible for some of the intense backscatter detected by VHF radar during equatorial spread F conditions.