Ionospheric origin O+ accelerated in the cusp/cleft region is one source for the O+ observed in the plasma sheet. This O+ is convected over the polar cap, flowing along open field lines to the tail lobes, and finally entering the plasma sheet. In this paper we use Cluster/CODIF data to study how the occurrence of cusp origin O+ in the polar cap and tail lobe changes over the solar cycle. Our study shows that the probability to observe cusp origin O+ decreases steeply during the declining phase of solar cycle 23 and starts to increase again at the start of the solar cycle 24. The decrease is much greater in the tail lobes than in the polar cap. A detailed analysis reveals that the O+ on the dominant transport path moves to higher latitudes in the Northern Hemisphere and more sunward in the Southern Hemisphere during the declining phase of the solar cycle (from the solar maximum to the solar minimum), so that the O+no longer reaches the near‐Earth (<20RE) tail lobes. This change in transport is consistent with a significantly reduced convection velocity and a northward shift of the cusp region as the solar activity decreases, so that the O+ moves much further along the field line before it is convected into the tail. It will therefore enter the plasma sheet much further down the tail.
Key Points
Cusp‐origin O+ in the lobe decreases during the solar cycle declining phase
The decrease rate is much larger in the tail lobes than in the polar cap
The transport paths have moved upward in the north and sunward in the south