Observations of a Kinetic-Scale Magnetic Hole in a Reconnection Diffusion Region

Magnetic holes have been widely observed in various space plasma systems. The origin of magnetic holes and their influence to background plasma are under debate. In this paper, we show a kinetic-scale electron vortex magnetic hole in a nonideal region of an active X line, which was observed by the Magnetospheric Multiscale mission at the dayside magnetopause. Intense current and nonideal electric field in the electron frame were observed within the magnetic hole, which led to a strong energy dissipation. Thus, the electron vortex magnetic hole probably provided an additional energy dissipation channel besides the electron diffusion region adjacent to the hole. We suggest that magnetic reconnection provided favorable conditions for the formation of this kinetic-scale magnetic hole and is an important source of magnetic holes in space plasma.