Microstructure of Magnetic Reconnection in Earth's Magnetotail

A recent study of magnetic reconnectiori in the earth's magnetotail dentified five events in which a pulse of heated electrons appeared near the end of an interval of fast tailward plasma flow. Further investigation of these events has revealed the following information on their microstructure' (1) Measurements of the electron Velocity distribution show that the temperature rise can be characterized as a true heating process, in that the gross evolution of the distribution is from a narrower to a. broader Maxwellian. (2) During the heating pulse abump is often apparent inthe tail of the electron distributiøn function at an energy of 2-5 keV. This bump could be the remnant of a beam produced by a 2to 5-kV parallel potential drop. Thus a possible mechanism for the heating of electrons is the beam plasma instability. (3) The magnetic field during these events is highly variable in all three components. Part of this variability may result from magnetic turbulence generated by the tearing mode instability, but minimum variance analysis uggests that some of the more rapid variations (up to 20 nT/s) are caused by rotational or tangential discontinuities. (4) Both the Y and Z components of the magnetic field are quite large (10-20 nT) at times. The strongest southward fields are usually observed near the beginning of the heating pulse, while the strongest Y components generally occur during the pre-heating interval of tailward plasma flow. Transient large-scale changes in the normal magnetotail current system are indicated by these observations.