Observation of low energy protons in the geomagnetic tail at lunar distances
Hardy, David Alfred
Freeman, John W.
Master of Science
Using the three Suprathermal Ion Detectors stationed on the moon, we have detected a region of plasma flowing anti-sunward along the ordered field lines of the geomagnetic tail. This plasma flow is found within the tail, hut exterior to the plasma sheet. It exhibits characteristics uniquely different from the other particle regimes traversed by the moon. The particles display an integral flux of from .1 to 9 x 1^7 ions/cm^2 sec ster, a bulk velocity of from 1 to 25 km/sec, temperatures in the range .4 to 5 x 1^5 degrees Kelvin and number densities between .1 and 5/cm^3. The magnetic field configuration for the times during which the particles were observed exhibits a direction and magnitude that is indicative of the lobes of the geomagnetic tail. In addition, no consistent deviation in the field is seen to correspond with the occurrence of the events. The events have an angular distribution extending over between 5 and 1 degrees. Spatially the events extend over a wide region in both the Y and Z directions. Continuous observations of these particles are seen over distances as great as 17 R in the Y direction and 12 R in the Z direction. The majority of the encounters with this flowing plasma, however, are found in a 12-RQ wide region adjoining the magnetopause. Also there are wide variations between tail passages as to the extent of time over which the particles are seen with an apparent correlation between the number of hours of observation and the Kp index averaged over these times. It is proposed that these particles may have entered through the cusp region. The particles could then be convected down towards the neutral plane by E x B drift and eventually be accelerated by a neutral line to produce the particles in the plasma sheet.