Measurements of horizontal drifts in theEandFregions at Millstone Hill

At Millstone Hill (42.6°N, 71.5°W) an oblique-incidence incoherent-scatter radar system has been employed to observe the drift of the ionospheric plasma in the E and F regions in directions across the earth's magnetic field. These measurements yield the true macroscopic motion of the ions rather than the motion of waves impressed in the plasma, but, owing to sensitivity limitations, measurements could be made only during the daytime when the electron density is large. It is found that the drift appears to be independent of altitude above about 180 km; this result suggests that the drift is caused by an electrostatic field. On the average the drift has an amplitude of about 25 m/sec (1 mv/m), and the direction rotates in a clockwise sense through 360° in 12 hours. The drifts observed at 130 km appear similar to the drifts in the F region, but in azimuth the direction lags behind the drift observed in the F region by 50°–60°. It appears that the electric field responsible for the drift in the F region is generated in the E region by the dynamo action of the solar semidiurnal (2, 2) tidal oscillation. On one day electric fields of magnetospheric origin developed following a magnetic storm sudden commencement. The clockwise progression of the drift was then reversed, and the drift reached 200 m/sec toward the west. This motion may be connected with the reported sunward surges of the plasma in the plasmasphere bulge at times of substorms.