Interchange Reconnection and ion kinetic instabilities in coronal plasma

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Abstract
The magnetic field in the chromosphere and low corona near the boundaries of equatorial coronal holes in the quiet Sun is thought to reconfigure through interchange reconnection (IR). This process occurs in low-beta plasma with a strong guiding field and may produce an ion distributions known as “hammerhead.” These distributions have been observed in coronal plasma associated with current sheets and in regions whose footpoints lie near equatorial coronal holes. They usually consist of a core plus a perpendicularly diffuse beam feature at a specific velocity relative to the core. The mechanism we propose involves the interpenetration of two plasmas with different properties—one on closed field lines and one on open field lines. In the chromosphere and low corona, these distributions can generate ion-sound and ion-cyclotron waves once the beam’s relative velocity exceeds a threshold. As such plasma distributions travel toward the solar wind through a funnel region where the magnetic field and plasma density rapidly drop, they may become unstable and produce Alfvén-type magnetic perturbations that can evolve nonlinearly into switchback structures. These threshold conditions are likely met near the transition from sub-Alfvénic to super-Alfvénic wind.