Initial Study on Coronal Plasma Jet Formation

Abstract

The sudden explosive events in the solar corona are thought to be best explained by ideal magnetohydrodynamic (MHD) instabilities and magnetic reconnection. One type of explosive event, the x-ray jet, has been observed to originate from ``anemone-type" active regions---dome-shaped magnetic structures appearing in a coronal hole. Despite the extent of research into coronal x-ray jets, however, there is no consensus on how the instabilities and reconnection play into these eruptions. For this thesis, a series of MHD simulations are conducted based on a concept, recently proposed by M. Yamada, in which the eruption of the x-ray jet is generated by the tilting of a half-spheromak type configuration, which induces magnetic reconnection near the top of the dome and releases the stored magnetic energy. These MHD simulations are initialized with a spheromak that is line-tied to a conducting boundary, and the evolution is determined by magnetically dominated (low-$\beta$) effects. In these simulations the initial line-tying and elongation of the spheromak can be controlled. The simulation computes both linear (ideal MHD instability) effects and nonlinear (magnetic reconnection) effects.

The central result of this thesis is that one-sided line-tying within the separatrix, a type of line-tying never before studied in spheromaks, can stabilize an elongated spheromak against the n=1 tilt mode. Most importantly, for a given amount of line-tying, an increase in elongation renders the spheromak unstable. This result offers a potential mechanism, elongation, for the sudden eruption of the coronal anemone-type structures. Finally, the simulations show that the spheromak tilt causes a current sheet to form near the separatrix, inducing the magnetic reconnection necessary for an eruptive event.