3D Magnetic Reconnection at a Coronal Null Point

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Nugget
Number: 329
1st Author: Maloney
2nd Author:
Published: 30 July 2018
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Introduction

Magnetic reconnection is believed to be the primary mechanism by which free energy stored in coronal magnetic fields is rapidly released during solar eruptive events. Unfortunately, owing to the small spatial scales on which reconnection is thought to occur, it is not directly observable by remote sensing of the solar corona. However, larger scale processes, such as associated inflows and outflows, plus signatures of accelerated particles, have been put forward as evidence of reconnection. Magnetic reconnection is often studied at X-points, the simplest view of the process in two dimensions.

In the case presented in this Nugget, we think instead that the reconnection occurs at a 3D coronal null point (Ref. [2]). This study employs data from many instruments: SDO/AIA, SDO/HMK, the Nançay Radiohelioaph and GOES (as well as RHESSI), in a study of the partial collapse of a coronal structure associated with a Type I radio storm (.pdf). We interpret the observations as evidence for accelerated electrons in the reconnection region responding to a gradual fall and rapid rise in electric drift velocity, in response to the inflowing and outflowing field lines at a 3D null point.

Observations

Figure 1 shows SDO/AIA observations of the passage of an X-shaped feature from the limb towards disk centre. The X-shaped feature appears to undergo a partial collapse on 6 July 2013 at approximately 09:45. Before this collapse four loop structures are visible in 171 A channel while after the collapse the northern and western segments are no longer visible

Figure 1: Overview of the collapse of the X-shaped coronal structure. Top: AIA 171 Â images covering the 90 minutes surrounding the collapse. Overlaid on the earliest image are the slices used to generate the timedistance plots shown in Figure 3. Slices A and B are 67 arcseconds and 96 arcseconds long, respectively; the arrow denotes the reference direction for the timedistance plots. Middle: Nançay Radioheliograph 430 MHz images showing the Type I storm source at the times of the above images. Overlaid is the field of view of the AIA images. Bottom: GOES 1-8 Â and RHESSI 3-6 keV light curves, showing the flares that occurred during the collapse. (from [Ref. 1]).

References

[1] "Three-dimensional magnetic reconnection in a collapsing coronal loop system"

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