  Coronal jets are observed above minority polarity intrusions throughout the
solar corona. Some of the most energetic occur on the periphery of active
regions where the magnetic field is strongly inclined. These jets exhibit a
non-radial propagation in the low corona as they follow the inclined field, and
often have a broad, helical shape. We present a three-dimensional
magnetohydrodynamic simulation of such an active-region-periphery helical jet.
We consider an initially potential field with a bipolar flux distribution
embedded in a highly inclined magnetic field, representative of the field
nearby an active region. The flux of the minority polarity sits below a
bald-patch separatrix initially. Surface motions are used to inject free energy
into the closed field beneath the separatrix, forming a sigmoidal flux rope
which eventually erupts producing a helical jet. We find that a null point
replaces the bald patch early in the evolution and that the eruption results
from a combination of magnetic breakout and an ideal kinking of the erupting
flux rope. We discuss how the two mechanisms are coupled, and compare our
results with previous simulations of coronal-hole jets. This comparison
supports the hypothesis that the generic mechanism for all coronal jets is a
coupling between breakout reconnection and an ideal instability. We further
show that our results are in good qualitative and quantitative agreement with
observations of active-region periphery jets.
