Opening of active region’s large-scale overlying magnetic loops and kinking motion of a magnetic loop triggered by a vicinal small eruption

Abstract

In this paper, we present a clear case of a small eruption near active region NOAA 10990 leading to opening of active region's large-scale magnetic loops and kinking motion of a magnetic loop in this active region on April 16, 2008. From a sequence of TRACE 171 images, we find that the upper large-scale overlying magnetic loops of the active region expanded upwards from the arcaded configuration to the vertical one accompanying the vicinal small eruption. At the same time, the topology of a magnetic loop inside the active region changed from the inverted "U" shape to the almost vertical one with its two legs intertwining each other. From the temporal analysis of the observations, we find that the opening of the upper large-scale overlying magnetic loops resulted in the instability of the magnetic loop inside the active region. By analyzing the surrounding coronal environment, we suggest that the existence of the lower overlying magnetic loops prevented the magnetic loop from eruption. Generally, the kinking motion of the flux rope is taken as occurrence of kink instability. In this event, the top of the magnetic loop first began the kinking motion and then the two legs intertwined each other. According to our knowledge, the latter process has not been reported. Because there was only one active region on the solar disk on April 16, 2008, it turned out to be a very good candidate for us to investigate the impact of the vicinal eruption on the active region. These findings provide evidence that the active region is very sensitive to the vicinal eruptions.