During away sectors of the interplanetary magnetic field (IMF) around autumnal equinox and toward IMF sectors around vernal equinox, Dst underwent an average 4.0 nT peak-to-peak diurnal oscillation during a 13-year analysis period. Such an oscillation is predicted by the Russell-McPherron effect. The same effect is also found in a case study showing Dst diurnally oscillating through a period of sustained, recurrent geomagnetic activity. The time of minimum Dst lags the time of maximum energy coupling as given by the Russell-McPherron effect by between 0.5 and 1.5 hours, which in the framework of the Russell-McPherron coupling model gives a measure of the energy flow time from the solar wind to the ring current. This lag seems to be significantly shorter than expected for the Russell-McPherron effect used as a driver to an energy input and decay model of ring current dynamics. The results suggest that a mechanism besides ring current decay might operate on the diurnal timescale, such as a flow of ring current energy into the ionosphere via the region 2 currents. ¿ American Geophysical Union 1996