DISPERSIVE O-SHEET BOUNDARY-LAYER WITH CRRES( CONICS OBSERVED IN THE PLASMA)LOMICS DURING A MAGNETIC STORM/

We present initial results from the Low-energy magnetospheric ion comp osition sensor (LOMICS) on the Combined release and radiation effects satellite (CRRES) together with electron, magnetic field, and electric field wave data. LOMICS measures all important magnetospheric ion spe cies (H+, He++, He+, O++, O+) simultaneously in the energy range 60 eV to 45 keV, as well as their pitch-angle distributions, within the tim e resolution afforded by the spacecraft spin period of 30 s. During th e geomagnetic storm of 9 July 1991, over a period of 42 min (0734 UT t o 0816 UT) the LOMICS ion mass spectrometer observed an apparent O+ co nic flowing away from the southern hemisphere with a bulk velocity tha t decreased exponentially with time from 300 km/s to 50 km/s, while it s temperature also decreased exponentially from 700 to 5 eV. At the on set of the O+ conic, intense low-frequency electromagnetic wave activi ty and strong pitch-angle scattering were also observed. At the time o f the observations the CRRES spacecraft was inbound at L approximate t o 7.5 near dusk, magnetic local time (MLT), and at a magnetic latitude of -23 degrees. Our analysis using several CRRES instruments suggests that the spacecraft was skimming along the plasma sheet boundary laye r (PSBL) when the upward-flowing ion conic arrived. The conic appears to have evolved in time, both slowing and cooling, due to wave-particl e interactions. We are unable to conclude whether the conic was causal ly associated with spatial structures of the PSBL or the central plasm a sheet.