Localized and Intense Energy Conversion in the Diffusion Region of Asymmetric Magnetic Reconnection

We analyze a high-resolution simulation of magnetopause reconnection observed by the Magnetospheric Multiscale (MMS) mission and explain the occurrence of strongly localized dissipation with amplitude more than an order of magnitude larger than expected. It arises from electrons that flow along the magnetosheath separatrices, converge in the diffusion region, and jet past the X-point. The resulting negative charge accumulation generates intense parallel electric fields that eject electrons along the magnetospheric separatrices and produce field-aligned beams observed by MMS.