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Abstract Using a two‐dimensional particle‐in‐cell simulation, we investigate the effects and roles of upper‐hybrid waves (UHW) near the electron diffusion region (EDR). The energy dissipation via the wave‐particle interaction in our simulation agrees withJ · E^′measured by magnetospheric multiscale (MMS) spacecraft. It means that UHW contributes to the local energy dissipation. As a result of wave‐particle interactions, plasma parameters which determine the larger‐scale energy dissipation in the EDR are changed. They‐directional current decreases while the pressure tensorP_yzincreases/decreases when the agyrotropic beam density is low/high, where(x, y, z)‐coordinates correspond the(L, M, N)‐boundary coordinates. Because the reconnection electric field comes from−∂P_yz/∂z, our result implies that UHW plays an additional role in affecting larger‐scale energy dissipation in the EDR by changing plasma parameters. We provide a simple diagram that shows how the UHW activities change the profiles of plasma parameters near the EDR comparing cases with and without UHW. 

Abstract National Aeronautics and Space Administration's Magnetosphere Multiscale mission reveals that agyrotropic electrons and intense waves are prevalently present in the electron diffusion region. Prompted by two distinct Magnetosphere Multiscale observations, this letter investigates by theoretical means and the properties of agyrotropic electron beam‐plasma instability and explains the origin of different structures in the wave spectra. The difference is owing to the fact that in one instance, a continuous beam mode is excited, while in the other, discrete Bernstein modes are excited, and the excitation of one mode versus the other depends on physical input parameters, which are consistent with observations. Analyses of dispersion relations show that the growing mode becomes discrete when the maximum growth rate is lower than the electron cyclotron frequency. Making use of particle‐in‐cell simulations, we found that the broadening anglein the gyroangle space is also an important factor controlling the growth rate. Ramifications of the present finding are also discussed.