PROBING PROPERTIES OF THE MAGNETOSPHERIC HOT PLASMA DISTRIBUTION BY WHISTLER-MODE WAVE INJECTION AT MULTIPLE FREQUENCIES - EVIDENCE OF SPATIAL AS WELL AS TEMPORAL WAVE GROWTH

This is the second of two papers on the use of whistler mode wave inje ction to investigate properties of the magnetospheric hot plasma. Pape r 1, [Sonwalkar et al., this issue] emphasized the use of signals at a single frequency to identify longitudinal structures ranging from 100 to 25,000 km in extent in similar to 1-10 keV electrons drifting azim uthally through whistler ducts. This short paper discusses and illustr ates the use of wave injection at multiple discrete frequencies to stu dy temporal changes in magnetospheric hot electrons with parallel (gyr oresonant) velocities in various nonoverlapping ranges. As in paper 1, the data studied were acquired during a special 9-hour period of 1.9 - 2.9 kHz VLF transmissions from Siple Station, Antarctica, to Lake Mi stissini, Canada, on January 23-24, 1988. The amplitudes of the leadin g edges of constant frequency pulses at 1900, 2150, and 2400 Hz were f ound to vary independently with time. This is interpreted as evidence of a spatial amplification process that accompanied the well known and more readily identifiable phenomena of exponential temporal growth to a saturation level. Evidence of wave-hot plasma interactions showed a dependence on df/dt of the input signal frequency versus time format; in general, the slow frequency ramps showed the highest amplitudes an d the fast ramps and parabolas the lowest, in agreement with past work .