HF Doppler radar observations of vertical and zonal plasma drifts–Signature of a plasma velocity vortex in evening F-region

Abstract

The simultaneous vertical and zonal plasma drift measurements using an HF Doppler radar system around March equinox of 1995 at the magnetic equatorial station, Trivandrum, India (8.33°N, 77°E, dip 0.4°N) are analyzed to evaluate the vector plasma drift at the F-region. It is found that the pre-reversal enhancement in vertical drift and the direction change of zonal drift from westward to eastward occur almost simultaneously. The velocity vector in the vertical-zonal plane, the resultant of vertical and zonal velocities, exhibits a gradual rotation in the evening time. The characteristics of velocity vector clearly promulgate the existence of a plasma velocity vortex in the equatorial F-region during post-sunset period.