PIC Simulations of Microinstabilities and Waves at Near-Sun Solar Wind Perpendicular Shocks : Predictions for Parker Solar Probe and Solar Orbiter Article - Septembre 2020

Zhongwei Yang, Ying Liu, Shuichi Matsukiyo, Quanming Lu, Fan Guo, Mingzhe Liu, Huasheng Xie, Xinliang Gao, Jun Guo

Zhongwei Yang, Ying Liu, Shuichi Matsukiyo, Quanming Lu, Fan Guo, Mingzhe Liu, Huasheng Xie, Xinliang Gao, Jun Guo, « PIC Simulations of Microinstabilities and Waves at Near-Sun Solar Wind Perpendicular Shocks : Predictions for Parker Solar Probe and Solar Orbiter  », The Astrophysical journal letters, septembre 2020, L24. ISSN 2041-8205

Abstract

Microinstabilities and waves excited at moderate-Mach-number perpendicular shocks in the near-Sun solar wind are investigated by full particle-in-cell simulations. By analyzing the dispersion relation of fluctuating field components directly issued from the shock simulation, we obtain key findings concerning wave excitations at the shock front : (1) at the leading edge of the foot, two types of electrostatic (ES) waves are observed. The relative drift of the reflected ions versus the electrons triggers an electron cyclotron drift instability (ECDI) that excites the first ES wave. Because the bulk velocity of gyro-reflected ions shifts to the direction of the shock front, the resulting ES wave propagates oblique to the shock normal. Immediately, a fraction of incident electrons are accelerated by this ES wave and a ring-like velocity distribution is generated. They can couple with the hot Maxwellian core and excite the second ES wave around the upper hybrid frequency. (2) From the middle of the foot all the way to the ramp, electrons can couple with both incident and reflected ions. ES waves excited by ECDI in different directions propagate across each other. Electromagnetic (EM) waves (X mode) emitted toward upstream are observed in both regions. They are probably induced by a small fraction of relativistic electrons. Results shed new insight on the mechanism for the occurrence of ES wave excitations and possible EM wave emissions at young coronal mass ejection-driven shocks in the near-Sun solar wind.

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