Numerical study of coronal plasma jet formation

A new scenario for solar flare eruption in the coronal holes is analyzed by using MHD stability concepts for a spheromak configuration. The stability properties of a spheromak partially embedded into a conducting surface are studied using three dimensional MHD simulations. In agreement with the analytical theory, a large degree of line-tying stabilizes the spheromak's tilt instability, while the elongation has a destabilizing effect. High-resolution nonlinear simulations also demonstrate current sheet formation at the upper surface of the spheromak, where the tilted magnetic field of the spheromak reconnects with the background magnetic field. The calculated stability threshold and the observed magnetic reconnection support a model of coronal jet eruptions where a dome-like magnetic structure grows through flux emergence on the solar surface, tilts, reconnects, and erupts. Countering the effect from elongation, line-tying strongly stabilizes a spheromak growing from a flux-emergence process, suggesting that to accelerate the onset of eruptive coronal jets, there must be magnetic reconnection at the bottom of the spheromak to detach the structure from the solar surface.