Behavior of mid-latitude F-region irregularities deduced from spaced-receiver VHF scintillation measurements

Abstract

Using three closely spaced antennas, mid-latitude night-time scintillations at 136 MHz were observed under geomagnetically quiet conditions during June–July 1982. By means of correlation analysis, characteristics of ionospheric irregularities such as drift velocities, shapes and sizes were investigated for seven scintillation events. In the premidnight hours mostly southward or southwestward drifts were observed, while in the postmidnight hours the percentage of northward drifts increased. Mean northward and southward drift velocities were 25 m s −1 and 23 m s −1, respectively. Large northward drifts (> 80m s −1) were occasionally observed in the postmidnight hours. Peculiar drift reversals from northward to southward occurred abruptly in the midst of strong and high-pitch scintillations. They were accompanied by sharp increases in TEC. The directions of the major axes of the diffraction pattern ellipses are coincident with those of the geomagnetic field lines, which suggests that the irregularities are well field-aligned. The mean axial ratio and mean minor radius are 6.2 and 182 m, respectively. The axial ratio increases and the minor radius decreases with increasing S 4.