Downward Drifting F-Region Irregularity Observed Above an Eastward Drifting One Before Midnight on 4 March 2014

On the night of 4 March 2014, the Hainan COherent Scatter Phased Array Radar (HCOPAR) observed two irregularities appearing simultaneously in the radar scope at different height ranges. The global positioning system total electron content receivers also recorded two groups of plasma bubbles connecting in the observation scope of the HCOPAR. The topside irregularity moved slowly downward with almost no zonal movement, while the bottomside irregularity drifted eastward. There was not much difference among the h'F, h(m)F, and f(o)F variations recorded by the Hainan Digisonde on that day and the reference days, except for a rapid descent in h(m)F between 20:45 and 21:15 LT. The downward moving irregularity was also recorded during this period. The prompt penetration electric fields induced by turnings of the interplanetary magnetic field Bz during weak geomagnetic activities are suggested not to influence the whole F-layer heights at low latitudes but only to change the drift direction of the topside irregularity.