New features of electron diffusion regions observed at subsolar magnetic field reconnection sites

Nineteen electron diffusion regions at magnetic field reconnection sites have been found in one hour of Cluster satellite data near the subsolar magnetopause. Investigations on previously unachieved spatial and temporal scales show the following for the first time: direct conversion of magnetic energy to electron energy (The resulting accelerated electrons, their field-aligned currents, and their post-acceleration fate were measured); the spatial dimensions of the large electric fields in the electron diffusion regions have an average thickness of 0.3 times the electron skin depth, in agreement with theory; and these electron diffusion regions were topological boundaries between open and closed magnetic field geometries that contained different plasma and magnetic field line flows. The electron diffusion regions were located at the magnetospheric separatrix where the magnetic field was large and the electron beta was less than one.