English: Magnetic reconnection zones (red) in the earth's magnetosphere. Labels: Solar wind, IMF: Interplanetary magnetic field, dayside magnetopause, plasmasheet, magnetotail. From NASA website article: MMS Magnetic Multiscale Code 461. Unlocking the Secrets of the Electron Diffusion Region. NASA Magnetospheric Multiscale Mission.
NASA caption from the source: Cosmic plasmas are threaded throughout with magnetic field lines of force. The field lines and the plasma are tied to one another and move together with the flow of the plasma. If magnetic fields in adjacent regions have opposite or significantly different orientations, the field lines and plasma can become coupled, with the individual field lines disconnecting from each other and then reconnecting with those in the adjacent region. When this happens, the energy stored in the magnetic fields is released as kinetic energy and heat. The disconnection and reconnection of the plasma and magnetic field lines takes place in a narrow boundary layer called the diffusion region.