Electrostatic Waves Around a Magnetopause Reconnection Secondary Electron Diffusion Region Modulated by Whistler and Lower‐Hybrid Waves

We investigate electrostatic waves in a magnetopause reconnection event around a secondary electron diffusion region. Near the current sheet mid‐plane, parallel electron beam‐mode waves are modulated by whistler waves. We conclude that the anisotropy of energized electrons in the reconnection exhaust excites whistler waves, which produce spatially modulated electron beams through nonlinear Landau resonance, and these beams excite beam‐mode electrostatic waves. In the separatrix region, parallel propagating electrostatic waves associated with field‐aligned electron beams and perpendicular propagating electron cyclotron harmonic waves with loss cone distributions exhibit modulation frequencies in the lower‐hybrid wave (LHW) frequency range. We infer that LHWs scatter electrons to produce beams and alter loss cones to modulate electrostatic waves. The results advance our understanding about the regimes and mechanisms of electrostatic waves in reconnection, with an emphasis on their coupling with lower‐frequency electromagnetic waves. Plain Language Summary Magnetic reconnection is an important energy dissipation process at the Earth's dayside magnetopause. In its central region, plasmas deviate from the thermal equilibrium and form structured distribution functions, which excite plasma waves. We investigate high‐frequency electrostatic waves in an event, where the waves are associated with electron beam—plasma interaction or anisotropy of distribution functions. We find that electrostatic waves are driven and modulated by lower‐frequency waves, as the latter alters the particle distribution functions. The results help us understand how various processes couple with each other to achieve the energy dissipation. Key Points Parallel electron beam‐mode waves are modulated by whistler near the current sheet mid‐plane, by driving beams through Landau resonance Electron beam‐mode and cyclotron waves are modulated by lower‐hybrid waves near separatrices, with beam and loss cone distributions