Investigating the Topology of the “Disconnection” of Coronal Holes

Using a potential-field-source-surface approximation, we construct an exact analytical model to describe the intrusion of a magnetic flux spot from the closed-field region into the polar coronal hole (CH). The spot, which has an opposite polarity compared to the surrounding field, moves across a local bulge in the CH, eventually detaching it into a separate minor CH. We show that the formation of a magnetic minimum point, its subsequent degeneration into a null point, and its bifurcation into a pair of nulls, plays a key role in this process. The separatrix field lines that emanate from the nulls form an interface between the open and closed field structures. This implies that the corresponding MHD evolution must involve magnetic reconnection to accommodate the redistribution of their magnetic fluxes. We anticipate that the reconnection outflows along the open part of the separatrix field lines may serve as a source of slow solar wind. Work supported by NASA and the Center for Integrated Space Weather Modeling (an NSF Science and Technology Center). Topological skeleton of the magnetic field in the neighborhood of a detached minor coronal hole; the skeleton consists of separatrix field lines emanating from two magnetic null points. The gray-shaded photospheric distribution of the squashing factor depicts the corresponding footprints of separatrix surfaces and quasi-separatrix layers.