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 injection to investigate properties of the magnetospheric hot plasma. Paper 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 ~1–10 keV electrons drifting azimuthally through whistler ducts. This short paper discusses and illustrates the use of wave injection at multiple discrete frequencies to study temporal changes in magnetospheric hot electrons with parallel (gyroresonant) 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 Mistissini, Canada, on January 23–24, 1988. The amplitudes of the leading edges of constant frequency pulses at 1900, 2150, and 2400 Hz were found 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/dtof the input signal frequency versus time format; in general, the slow frequency ramps showed the highest amplitudes and the fast ramps and parabolas the lowest, in agreement with past work.