Whistler and Broadband Electrostatic Waves in the Multiple X-Line Reconnection at the Magnetopause

We investigate whistler-mode waves and broadband electrostatic waves (EWs) within an ion diffusion region (IDR) at the magnetopause. The quasi-parallel whistlers are observed in the separatrix regions associated with the electron anisotropy or loss cone, while the oblique whistlers, the Buneman-type waves, and the oblique EWs are observed in the center of the current sheet associated with the accelerated electron or ion beams. The whistlers are linked with Buneman-type waves by the electron Pacman distribution rather than the wave-wave process. The accelerated cold electron beams excite the Buneman-type instabilities and make the anisotropy or loss cone of hot electrons less apparent, which led to the conversion of the whistlers from quasi-parallel to oblique. Additionally, the oblique EWs are associated with the ion beams produced by the multiple X-line reconnection. These results provide a further understanding of the relation between plasma waves and plasma kinetics in the IDR. Plain Language Summary The whistler waves and the broadband electrostatic waves are two common waves produced by magnetic reconnection in space plasma. Generally, the whistler waves have two modes, the quasi-parallel and the oblique to the ambient magnetic field associated with different generation mechanisms. Both of them have been observed in the magnetic reconnection, but their relation is still unclear. The broadband electrostatic waves are sometimes simultaneously observed with the oblique whistlers. The relationship between them is also inconclusive. Here, we present a new view of the relation between the quasi-parallel whistlers, the oblique whistlers, and the broadband electrostatic waves. They are linked by the evolution of electron Pacman distribution, which is composed of the hot magnetospheric population with the loss cone and the cold accelerated magnetosheath beam characteristic for magnetopause reconnection, in the reconnection diffusion region rather than the wave-wave process. Besides, the oblique electrostatic waves associated with ion beams are observed in the diffusion region. These results advance our understanding of the relation between plasma waves and magnetic reconnection.