Geomagnetic pulsations in the 10- to 200-s (Pc 3--4) period range as observed at the earth's surface are often seen to switch on and off during the day. Recordings of earth current measurements made at three stations in the United Kingdom (geomagnetic latitude 55¿-61¿N, L=2.6--3.6) were compared with measurements of the interplanetary magnetic field (IMF) made by the Heos 2 satellite. Some events are presented which show a distinct correlation between enhancements in the radial component of the IMF and the amplitude of pulsations in the period range 20--60 s. Computation of the cross-correlation functions suggests a possible diurnal variation in the delay time between the step observed in the IMF and the enhancement of pulsations at the ground (typically ~15 min). These observations may give important indications of the generation regions of these ULF waves in the magnetosphere.