Whistler Waves Associated With Electron Beams in Magnetopause Reconnection Diffusion Regions

Whistler waves are often observed in magnetopause reconnection associated with electron beams. We analyze seven MMS crossings surrounding the diffusion region (EDR) to study role of beams whistler excitation. Waves have two major types: (a) Narrow-band high ellipticities and (b) broad-band that more electrostatic significant variations wave normal angles. While both types beams, key difference is anisotropy background population, perpendicular parallel anisotropies, respectively. The linear instability analysis suggests first type mainly due anisotropy, beam contributing additional cyclotron resonance enhance growth. second broadband excited via Landau resonance, as seen one event, induces an mode. results supported by particle-in-cell simulations. infer occurs downstream central EDR, where electrons experience Betatron acceleration form anisotropy; EDR guide field reconnection. A parametric conducted analysis. alone above ?3 likely excites mode waves. Large drifts cause Doppler shifts may lead left-hand polarizations ion frame. Future studies needed determine whether observation covers a broader parameter regime understand competition between other instabilities.