Measurements of magnetic and electric fields in the summer polar cap during periods when Bz>0 have revealed a stable well-developed ''W'' pattern in the transverse component of B¿ and in the orbit parallel component of Ē (Iijima et al., 1984; Burke et al., 1979). This W pattern found in B¿ and E¿ characterizes a four-celled ion drift pattern having sunward flow in the central polar cap flanked by regions of antisunward flow that reverses to sunward once again at lower latitudes. Subsequent investigation of electric and magnetic fields from the S3-2 and Magsat data sets shows that in the summer hemisphere a transition from this W shape into a more structured pattern occurs near the magnetic dawn-dusk meridian. Since, on a seasonal basis, Magsat's orbit remained fixed with respect to the terminator, the conductivity distribution beneath the orbit track was essentially constant from one orbit to the next. Thus, this effect is not due to conductivity variations. In the winter polar cap the W pattern is difficult to identify in the measurements of the transverse component of B¿ or Ē made on either side of magnetic dawn-dusk; however, analysis of the radial component of B¿ measured in both polar caps at, or tailward of, the dawn-dusk meridian shows the presence of a weak ionospheric Hall current system with a W-shaped distribution for scale sizes >600 km. From these observations we conclude that a basic two-cell reverse convection pattern persists in the polar caps of both hemispheres and on both sides of the dawn-dusk meridian (in addition to the auroral viscous cells). These polar cells are distorted in the tail side of the sunlit hemisphere and in the entire dark hemisphere, with major perturbations in the sunward-antisunward direction. This is related to an irregular reconnection process in the plasma sheet driven by opposing dawn-dusk and dusk-dawn electric fields that have their sources in the boundary layer and solar wind, respectively. This process gives rise to the ionospheric turbulence observed in the electric field and Birkeland current signature and may be associated with sun-aligned arcs.