A Model for Coronal Hole Bright Points and Jets Due to Moving Magnetic Elements

Abstract

Coronal jets and bright points occur prolifically in predominantly unipolar magnetic regions, such as coronal holes (CHs), where they appear above minority-polarity intrusions. Intermittent low-level reconnection and explosive, high-energy-release reconnection above these intrusions are thought to generate bright points and jets, respectively. The magnetic field above the intrusions possesses a spine-fan topology with a coronal null point. The movement of magnetic flux by surface convection adds free energy to this field, forming current sheets and inducing reconnection. We conducted three-dimensional magnetohydrodynamic simulations of moving magnetic elements as a model for coronal jets and bright points. A single minority-polarity concentration was subjected to three different experiments: a large-scale surface flow that sheared part of the separatrix surface only, a large-scale surface flow that also sheared part of the polarity inversion line surrounding the minority flux, and the latter flow setup plus a "flyby" of a majority-polarity concentration past the moving minority-polarity element. We found that different bright-point morphologies, from simple loops to sigmoids, were created. When only the field near the separatrix was sheared, steady interchange reconnection modulated by quasi-periodic, low-intensity bursts of reconnection occurred, suggestive of a bright point with periodically varying intensity. When the field near the polarity inversion line was strongly sheared, on the other hand, filament channels repeatedly formed and erupted via the breakout mechanism, explosively increasing the interchange reconnection and generating nonhelical jets. The flyby produced even more energetic and explosive jets. Our results explain several key aspects of CH bright points and jets, and the relationships between them.