Diurnal oscillation of Dst: A manifestation of the Russell‐McPherron effect

Abstract

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.