High-speed translunar magnetotail plasma flows
Shull, Peter Otto
Freeman, John W.
Master of Science
Unusual, high-speed flows of plasma away from the Sun in the translunar magnetotail are discovered to occur persistently. Faster, cooler, and less dense than the plasma flows customarily encountered in the translunar magnetotail, these flows suggest that small-scale magnetic merging occurs regularly in the plasma sheet. Particle and field data from eight and one-half magnetotail crossings are studied, making this the most extensive survey to date. Those crossings are chosen for which there are magnetometer data from Explorer 35 and particle data from the Rice Suprathermal Ion Detector Experiment (SIDE) set up on the Moon by the crew of Apollo 14. This SIDE, like its twins from Apollos 12 and 15, measures plasma energy distributions in the energy/charge range between 1 and 35 eV/q. Computer reduction of these SIDE data yields plasma bulk speeds, temperatures, and densities. With the assumption that the plasma is entirely hydrogen, it is found that the plasma flows are characterized by bulk velocity u = 25 to 7 km/s, ion temperature kT = 5 to 1 eV, and ion density n = .1 to .1 cm. Most of these flows ("bubble" flows) occur within one or two hours of changes in tail magnetic field strength and direction, changes suggesting the passage of the Moon near a magnetic bubble. Two or three flows ("lobe" flows) are associated exclusively with >= 1/y magnetic fields parallel or anti-parallel to the Earth-Sun axis. Neither type of flow is directly related to solar or geomagnetic activity. The transfer of magnetic field energy to mantle plasma in the cislunar magnetotail may cause the bubble flows. Appearances of doubly peaked plasma energy distributions are briefly discussed. The origin of the lobe flows is uncertain. If the field lines associated with them map into a magnetic bubble, the flows are probably bubble flows observed farther than usual from their places of origin. If the field lines map into the polar regions of Earth, then the lobe flows may be ions such as H+, He+, He++, and + escaping from the polar ionospheres.