Numerical simulation of a fundamental mechanism of solar eruption with a range of magnetic flux distributionsx22c6;

Solar eruptions are an explosive release of coronal magnetic field energy manifested as solar flares and coronal mass ejections. Observations have shown that the core of eruption-productive regions are often a sheared magnetic arcade, namely, a single bipolar configuration, and, in particular, the corresponding magnetic polarities at the photosphere are elongated along a strong-gradient polarity inversion line (PIL). It remains unclear what mechanism triggers the eruption in a single bipolar field and why the one with a strong PIL is favorable for producing eruption. Recently, using highly accurate simulations, we established the fundamental mechanism behind solar eruption initiation by which a bipolar field driven by quasi-static shearing motion at the photosphere can form an internal current sheet, followed by fast magnetic reconnection that triggers and drives the eruption. Here, we investigate the behavior of the fundamental mechanism with different photospheric magnetic flux distributions, namely, magnetograms, by combining a theoretical analysis and a numerical simulation. Our study shows that the bipolar fields of different magnetograms, sheared continuously, all exhibit similar evolutions - from slow storage to the fast release of magnetic energy - that are in accordance with the fundamental mechanism and demonstrate the robustness of the proposed mechanism. Furthermore we found that the magnetograms with a stronger PIL produce larger eruptions and the key reason is that the sheared bipolar fields with a stronger PIL can achieve more non-potentiality and their internal current sheet can form at a lower height and with a higher current density, by which the reconnection can be more efficient. This also provides a viable trigger mechanism for the observed eruptions in active regions with a strong PIL.