Experimental investigation of possible geomagnetic feedback from energetic (0.1 to 16 keV) terrestrial O + ions in the magnetotail current sheet

Data from energetic ion mass spectrometers on the ISEE 1 and AMPTE/CCE spacecraft are combined with geomagnetic and solar indices to investigate, in a statistical fashion, whether energized O + ions of terrestrial origin constitute a source of feedback which triggers or amplifies geomagnetic activity, as has been suggested in the literature, by contributing a destabilizing mass increase in the magnetotail current sheet. The ISEE 1 data (0.1‐16 keV/e) provide in situ observations of the O + concentration in the central plasma sheet, inside of 23 R E , during the rising and maximum phases of solar cycle 21, as well as inner magnetosphere data from same period. The CCE data (0.1‐17 keV/e), taken during the subsequent solar minimum, all within 9 R E , provide a reference for long‐term variations in the magnetosphere O + content. Statistical correlations between the ion data and the indices, and between different indices, all point in the same direction: there is probably no feedback specific to the O + ions, in spite of the fact that they often contribute most of the ion mass density in the tail current sheet.