Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm11c1773k&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SM11C-1773
Physics
[5737] Planetary Sciences: Fluid Planets / Magnetospheres, [5754] Planetary Sciences: Fluid Planets / Polar Regions, [5794] Planetary Sciences: Fluid Planets / Instruments And Techniques
Scientific paper
On June 4, 2008 UT, the position of the satellite Io with respect to Jupiter was the so-called Io-A, we observed Jovian decametric (DAM) radio emissions using a waveform receiver (WFR). The frequency range was 21-23 MHz and polarization was RH. We detected negative spectra at negative drift rates of approximately 5 MHz/s quenched background DAM emissions. We called this phenomenon as slow-drift shadow (SDS) events. 38 minutes after the detection of the SDS events, the background DAM emissions that exhibited wave modulations (WMs). The SDS events and WMs are considered to be the same phenomenon, because both phenomena quenched the background L-burst emissions at a negative drift rate of approximately 5 MHz/s. Sudden SDS slope changes occurred once or twice in the frequency range of 21.4 to 22.1 MHz. WMs appeared four times at intervals of approximately 7 min for durations of 3-10 s each. Furthermore, we found that the positive drift rates of WMs were several times higher than the negative drift rates. A part of the spectrum of the WMs was extracted from the dynamic spectra whose bandwidth was 50 kHz. The modulation frequency of the WMs was determined by using Fourier transformation of the spectrum. We found that the WMs had fundamental frequencies of 2.5-5 Hz, and the 1st and 2nd harmonics of these frequencies were odd resonances at the fundamental frequencies. We consider that the SDS events may be related to E|| in DAM source region. The 7-min intervals of WMs are consistent with the characteristic period of Alfven waves that are trapped along the magnetic field lines that link the northern and southern polar regions of Jupiter via the Io plasma torus, suggesting the existence of ionospheric Alfven resonator (IAR) expected in the system of Jupiter. It is known that inertial Alfven waves can accelerate electrons up to tens of kiloelectron volts above the polar regions of Jupiter, where the Alfven velocity approaches the light velocity. With the assumption that the SDS events and WMs were induced through the interaction between these accelerated electrons and the mechanism that generated the background DAM emissions, the estimated bulk energies of the electrons accelerated toward Jupiter are several kiloelectron volts and those of the electrons accelerated away from Jupiter are hundreds of electron volts. We suppose that strong Alfven waves arrived at the northern polar region of Jupiter at intervals of approximately 7 min; these resonated in the IAR within a few seconds and gave rise to the WMs in the DAM emissions. In this research, we suggest the existence of IAR in the system of Jupiter by using a WFR and the millisecond modulations of Jovian L-burst emissions.
Koshida Tomonori
Misawa Hiroaki
Shibata Tadahiro
Taguchi Satoshi
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