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The rotation of sunspots around their umbral center has long been consideredas an important process in leading to solar eruptions, but the underlyingmechanism remains unclear. A prevailing physical picture on how sunspotrotation leads to eruption is that, by twisting the coronal magnetic fieldlines from their footpoints, the rotation can build up a magnetic flux rope anddrive it into some kinds of ideal magnetohydrodynamics (MHD) instabilitieswhich initiate eruptions. Here with a data-inspired MHD simulation we studiedthe rotation of a large sunspot in solar active region NOAA 12158 leading to amajor eruption, and found that it is distinct from prevailing theories based onideal instabilities of twisted flux rope. The simulation suggests that, throughsuccessive rotation of the sunspot, the coronal magnetic field is sheared witha central current sheet created progressively within the sheared arcade beforethe eruption, but without forming a flux rope. Then the eruption is instantlytriggered once fast reconnection sets in at the current sheet, while a highlytwisted flux rope is created during the eruption. Furthermore, the simulationreveals an intermediate evolution stage between the quasi-static energy-storagephase and the impulsive eruption-acceleration phase. This stage may correspondto the slow-rise phase in observation and it enhances building up of thecurrent sheet.

Magnetic Reconnection as the Key Mechanism in Sunspot Rotation Leading to Solar Eruption