Observation of Magnetic Reconnection at a 3d Null Point Associated With a Solar Eruption

Abstract

Magnetic null has long been recognized as a special structure serving as a preferential site for magnetic reconnection (MR). However, the direct observational study of MR at null-points is largely lacking. Here, we show the observations of MR around a magnetic null associated with an eruption that resulted in an M1.7 flare and a coronal mass ejection. The GOES Xray profile of the flare exhibited two peaks at ∼02:23 UT and ∼02:40 UT on 2012 November 8, respectively. Based on the imaging observations, we find that the first and also primary Xray peak was originated from MR in the current sheet underneath the erupting magnetic flux rope (MFR). On the other hand, the second and also weaker X-ray peak was caused by MR around a null-point located above the pre-eruption MFR. The interaction of the null-point and the erupting MFR can be described as a two-step process. During the first step, the erupting and fast expanding MFR passed through the null-point, resulting in a significant displacement of the magnetic field surrounding the null. During the second step, the displaced magnetic field started to move back, resulting in a converging inflow and subsequently the MR around the null. The null-point reconnection is a different process from the current sheet reconnection in this flare; the latter is the cause of the main peak of the flare, while the former is the cause of the secondary peak of the flare and the conspicuous high-lying cusp structure.

Solar Coronal Loop Dynamics Near the Null Point Above Active Region NOAA 2666

“…In contrast to events studied by Su et al (2013), Sun et al (2015Sun et al ( , 2016, and Xue et al (2016), the outflow velocity in our event is not much greater than the inflow velocity. The inflow velocity is of the same order as reported by Sun et al (2015Sun et al ( , 2016, while the outflow velocity is lower by nearly an order of magnitude. It should be noted that in our event plasma outflows into the reconnection region in the vertical direction and outflows in the horizontal direction.…”

“…The observed velocities are very slow comparative to ones reported in other studies of coronal reconnection (Su et al 2013;Sun et al 2016;Xue et al 2016); however, Sun et al (2015Sun et al ( , 2016 reported the velocities of the inflows varying from 0.1 to 3.7 km s −1 in reconnection in the wake of an erupting flux rope and the inflow velocity in a range of 1-10 km s −1 in another eruptive event. In contrast to events studied by Su et al (2013), Sun et al (2015Sun et al ( , 2016, and Xue et al (2016), the outflow velocity in our event is not much greater than the inflow velocity. The inflow velocity is of the same order as reported by Sun et al (2015Sun et al ( , 2016, while the outflow velocity is lower by nearly an order of magnitude.…”

“…It should be noted that in our event plasma outflows into the reconnection region in the vertical direction and outflows in the horizontal direction. In the events studied by Su et al (2013), Sun et al (2015, 2016), and Xue et al (2016), the situation is opposite. All these events were more dynamic and X-typed structures seemed to be temporary.…”

Plasmoids and Resulting Blobs due to the Interaction of Magnetoacoustic Waves with a 2.5D Magnetic Null Point

“…As a matter of fact, the flows cover a limited area during the first reconnection which is expectable and the value of the amplitude of the velocity magnifies due to the reconnection. Sun et al (2012); Liu et al (2013); Sun et al (2016) expressed that intense emission areas do not occur in magnetic reconnection sites. The question is why intense emission does not occur during the magnetic reconnection event.…”

How Alfvén waves induce compressive flows in the neighborhood of a 2.5D magnetic null-point

“…A reconnection site provides a foundation for studying various aspects of wave dynamics, especially the interaction of waves with the null-point itself. A reconnection site in the solar atmosphere hosts solar flares 22 and coronal mass ejections 23 which are strong enough to affect the Earth's atmosphere.…”