Jovian slow-drift shadow events

摘要

[1] We observed negative spectra of quenched background L burst emissions with anegative drift rate of -5 MHz s~(-1)by using a waveform receiver developed byKoshida[2009]. We named this phenomenon a slow-drift shadow event (SDS event). The leadingand trailing edges of these SDS events showed a sudden change in their drift rates atsimilar frequencies. Wavy SDS-like phenomena were also observed with a frequency of15 Hz. Both S bursts and the ionospheric Alfven resonator have similar characteristicfrequencies. The local potential jumps were discovered near the Jovian decametric (DAM)source regions by Hess et al. (2007b, 2009). SDS slope changes may be related to similarfeatures. We have attempted to quantitatively estimate the background plasma densities byassuming that the background L burst emissions were generated by cyclotron maserinstability (CMI) and that the SDS events were related to the Alfven wave. The estimatedbackground plasma densities were in the range of 5 x 106-2 x 107 cm-3. Since fpf,0.87-1.7, the CMI must be quenched. This give rises to the question of what induced theSDS events.