Formation of Negative J ⋅ E ′ in the Outer Electron Diffusion Region During Magnetic Reconnection

It is widely acknowledged that positive energy dissipation J ⋅ E′ from the fields to the plasmas occurs in the electron diffusion region (EDR) during magnetic reconnection. There also exists negative J ⋅ E′ in the outer EDR, but what causes such negative J ⋅ E′ is still unclear. In the present study, we applied 2.5-D particle-in-cell simulation to investigate what causes the negative J ⋅ E′ in the outer EDR through generalized Ohm's law. It is found that the region of negative J ⋅ E′ expands in space with the evolution of magnetic reconnection, and the embodiment of negative J ⋅ E′ is dominated by the electron inertial term in the generalized Ohm's law due to the deceleration of the electrons in the outer EDR. This deceleration is caused by the opposite electric field compared with the ones in the inner EDR. And the opposite electric field is induced by the newly reconnected magnetic field lines in the outer EDR. Our results give a new perspective of energy transformation between the fields and the plasmas during magnetic reconnection.