Superhalo electrons appear to be continuously present in the interplane- tary medium, even during very quiet times, with a power-law spectrum at energies above ～2 keV. Here we numerically investigate the generation o...Superhalo electrons appear to be continuously present in the interplane- tary 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 magnetohydrody- namics 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 mag- netic 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 elec- trons, 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 dis- plays a power-law distribution at ～ 2-100 keV, f（E）～ E^-δ, with a 6 of ～1.5 - 2.4. For single （multiple） X-line reconnection, the spectrum becomes harder （softer） as the anomalous resistivity parameter a （uniform resistivity η） increases. These modeling results suggest that the acceleration in the solar wind source region may contribute to superhalo electrons.展开更多
基金Supported by the National Natural Science Foundation of China
文摘Superhalo electrons appear to be continuously present in the interplane- tary 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 magnetohydrody- namics 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 mag- netic 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 elec- trons, 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 dis- plays a power-law distribution at ～ 2-100 keV, f（E）～ E^-δ, with a 6 of ～1.5 - 2.4. For single （multiple） X-line reconnection, the spectrum becomes harder （softer） as the anomalous resistivity parameter a （uniform resistivity η） increases. These modeling results suggest that the acceleration in the solar wind source region may contribute to superhalo electrons.
