Clear spectroscopic evidence for magnetic reconnection in solar filament structure splitting

Researchers reveal specific spectral evidence for magnetic reconnection in the splitting of the solar filament structure

Partial cleavage and bursting of the filament structure. (a)–(f) SDO/AIA images 304 Å ((a)–(c), (f)) and 131 ((d)–(e)). (g) Time-distance profile generated by stacking AIA 304 images along the dashed line in (a), overlaid with GOES-15 1–8 X-ray flux in cyan. The field of view (FOVs) of (a)–(f) is the same, whose coordinates are rotated differently and aligned to those of (b). “F1” and “F2” in (a), (c), (f) and (g) denote the lower and upper capillary branches, respectively. In (b) the arrow indicates a bright area between the two branches indicative of cleavage. “E1” and “E2” in (d)–(e) denote two flares associated with the partial eruption. In (g) the dotted line on the left indicates the approximate time of division, and the two pairs of close arrows show the total width of the two branches of the filaments before and after division; The dashed dashed lines indicate the peak times of the X-ray flux for the “E1” and “E2” flares. The dashed rectangle in (b) represents the raster field of view of IRIS displayed in Figures 2(c)–(e), and the two short vertical bars in (g) indicate that raster duration overlapping with division. Animation is available for (a) – (c) starting at 07-13T22:00 UT and ending at 07-14T06:00 UTC. Lines, arrows, and other annotations in the animation are removed. The duration of the real-time animation is ∼34 sec. credit: Astrophysical Journal Letters (2022). DOI: 10.3847/2041-8213/ac9dfd

Magnetic reconnection is a global process that changes the magnetic structure and converts magnetic energy into plasma kinetic energy. Spatially resolved spectral observations covering extended regions in the solar atmosphere are scarce, and thus the distribution and energy splitting of reconnection remain unclear.

a strings It is darker and more dense in structure solar atmosphere. Doppler shifts of bidirectional flows, as conclusive evidence of reconnection, were not detected in Solar strings split so far.

However, researchers led by Dr Hu Huidong of the National Space Science Center of the Chinese Academy of Sciences, along with collaborators from the Max Planck Institute for Solar System Research in Germany and Nanjing University in China, have reported Magnetic reconnection An event that caused the solar filament structure to split, based on spatially resolved spectral data from the Interface Area Imaging Spectrometer (IRIS) and images from the Solar Dynamics Observatory (SDO).

The study has been published in Astrophysical Journal Letters.

“The filament structure was divided into upper and lower branches by magnetic reconnection, which eventually partially broke, with the upper branch ejected and the lower branch retained,” said Dr. Hu.

credit: Astrophysical Journal Letters (2022). DOI: 10.3847/2041-8213/ac9dfd

Large adjacent blue and red offsets (>50 km/s) of the Si IV line are detected in the bright region between the two branches of the filaments, which spatially correspond to large non-thermal widths and enhanced intensity of the Si IV line. These are clear signals of magnetic reconnection. The length of the unprecedented reconnection area is no less than 14,000 km.

The double Gaussian fit of the line spectra shows a blue-red shift (up to ~150 km/s) for the up- and downstream outflows. Reduction of the total linewidth indicated that line-of-sight velocities decreased significantly after the bidirectional outflows left the reconnection site. The broadening of the line on the blue wing is observed several arc seconds away from the reconnection site, which may indicate turbulence that occurred when the updraft interacted with the upper filament branch.

Differential emission measurement analysis showed that the temperature during reconnection was ~14 MK, ~9 MK higher than that before reconnection. the electron density was ~3.9 x 1010 cm-3About twice that before reconnection. The total thermal energy has been estimated to be about 1.3 x 1027 ergs, which was much larger than Kinetic energy.

“Our study provided definitive spectral evidence of filament structure cleavage by magnetic reconnection,” said Dr Hu. “Reconnection is taking place in an extended region of unprecedented length, and thermal energy overwhelmingly dominates over kinetic energy in this reconnection event.”

more information:
Huidong Hu et al, Spectral and imaging observations of spatially extended magnetic reconnection in solar filament structure splitting, Astrophysical Journal Letters (2022). DOI: 10.3847/2041-8213/ac9dfd

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