Vol 15, No 3

Numerical simulation of superhalo electrons generated by magnetic reconnection in the solar wind source region

Li-Ping Yang, Ling-Hua Wang, Jian-Sen He, Chuan-Yi Tu, Shao-Hua Zhang, Lei Zhang, Xue-Shang Feng


Abstract Superhalo electrons appear to be continuously present in the interplanetary medium, even during very quiet times, with a power-law spectrum at energies above ~2 keV. Here we numerically investigate the generation of superhalo electrons by magnetic reconnection in the solar wind source region, using magnetohydrodynamics and test particle simulations for both single X-line reconnection and multiple X-line reconnection. We find that the direct current electric field, produced in the magnetic reconnection region, can accelerate electrons from an initial thermal energy of T ~ 105 K up to hundreds of keV. After acceleration, some of the accelerated electrons, together with the nascent solar wind flow driven by the reconnection, propagate upwards along the newly-opened magnetic field lines into interplanetary space, while the rest move downwards into the lower atmosphere. Similar to the observed superhalo electrons at 1 AU, the flux of upward-traveling accelerated electrons versus energy displays a power-law distribution at ~ 2−100 keV, f (E) ~ E−δ, with a δ of ~ 1.5 − 2.4. For single (multiple) X-line reconnection, the spectrum becomes harder (softer) as the anomalous resistivity parameter α (uniform resistivity η) increases. These modeling results suggest that the acceleration in the solar wind source region may contribute to superhalo electrons.


Keywords acceleration of particles — methods: numerical — Sun: particle emission — (Sun:) solar wind — Sun: transition region

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