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Microinstabilities and waves excited at moderate-Mach-number perpendicularshocks in the near-Sun solar wind are investigated by full particle-in-cell(PIC) simulations. By analyzing the dispersion relation of fluctuating fieldcomponents directly issued from the shock simulation, we obtain key findingsconcerning wave excitations at the shock front: (1) at the leading edge of thefoot, two types of electrostatic (ES) waves are observed. The relative drift ofthe reflected ions versus the electrons triggers an electron cyclotron driftinstability (ECDI) which excites the first ES wave. Because the bulk velocityof gyro-reflected ions shifts to the direction of the shock front, theresulting ES wave propagates oblique to the shock normal. Immediately, afraction of incident electrons are accelerated by this ES wave and a ring-likevelocity distribution is generated. They can couple with the hot Maxwelliancore and excite the second ES wave around the upper hybrid frequency. (2) fromthe middle of the foot all the way to the ramp, electrons can couple with bothincident and reflected ions. ES waves excited by ECDI in different directionspropagate across each other. Electromagnetic (EM) waves (X mode) emitted towardupstream are observed in both regions. They are probably induced by a smallfraction of relativistic electrons. Results shed new insight on the mechanismfor the occurrence of ES wave excitations and possible EM wave emissions atyoung CME-driven shocks in the near-Sun solar wind.

PIC simulations of microinstabilities and waves at near-Sun solar wind perpendicular shocks: Predictions for Parker Solar Probe and Solar Orbiter