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We address the formation of 3D nullpoint topologies in the solar corona bycombining Hinode/XRT observations of a small dynamic limb event, which occurredbeside a non-erupting prominence cavity, with a 3D zero-beta MHD simulation. Tothis end, we model the boundary-driven kinematic emergence of a compact,intense, and uniformly twisted flux tube into a potential field arcade thatoverlies a weakly twisted coronal flux rope. The expansion of the emerging fluxin the corona gives rise to the formation of a nullpoint at the interface ofthe emerging and the pre-existing fields. We unveil a two-step reconnectionprocess at the nullpoint that eventually yields the formation of a broad 3Dfan-spine configuration above the emerging bipole. The first reconnectioninvolves emerging fields and a set of large-scale arcade field lines. Itresults in the launch of a torsional MHD wave that propagates along thearcades, and in the formation of a sheared loop system on one side of theemerging flux. The second reconnection occurs between these newly formed loopsand remote arcade fields, and yields the formation of a second loop system onthe opposite side of the emerging flux. The two loop systems collectivelydisplay an anenome pattern that is located below the fan surface. The flux thatsurrounds the inner spine field line of the nullpoint retains a fraction of theemerged twist, while the remaining twist is evacuated along the reconnectedarcades. The nature and timing of the features which occur in the simulation doqualititatively reproduce those observed by XRT in the particular event studiedin this paper. Moreover, the two-step reconnection process suggests a newconsistent and generic model for the formation of anemone regions in the solarcorona.

Fan-spine topology formation through two-step reconnection driven by twisted flux emergence